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Many bacterial pathogens utilize a specialized secretion system, termed type III secretion system (T3SS), to translocate effector proteins into host cells and establish bacterial infection. The T3SS is anchored within the bacterial membranes and contains a long needle/filament that extends toward the host-cell and forms, at its distal end, a pore complex within the host membrane. The T3SS pore complex consists of two bacterial proteins, termed SctB and SctE, which have conflicting targeting indications; a signal sequence that targets to secretion to the extracellular environment via the T3SS, and transmembrane domains (TMDs) that target to membrane localization. In this study, we investigate whether the TMD sequences of SctB and SctE have special features that differentiate them from classical TMDs and allow them to escape bacterial membrane integration. For this purpose, we exchanged the SctB and SctE native TMDs for alternative hydrophobic sequences and found that the TMD sequences of SctB and SctE dictate membrane destination (bacterial versus host membrane). Moreover, we examined the role of the SctB TMD sequence in the activity of the full-length protein, post secretion, and found that the TMD does not serve only as a hydrophobic segment, but is also involved in the ability of the protein to translocate itself and other proteins into and across the host cell membrane.

The emergence of antibiotic resistance has been raised due to the inappropriate use of antibiotics that might be the urgent health crisis. Antibiotics in animals and food chain have been widely used as growth promoters, prophylaxis, and treatment of infectious diseases, which provides the selective pressure on foodborne pathogens. It is essential to develop novel therapeutic weapon for controlling the appearance of resistance and inhibiting imminent threat of pandemics possible by means of multidrug resistant (MDR) pathogens. Nowadays, the control of MDR pathogens has been improved with the development of bacteriophage (phage)-based approaches such as single phage therapy, synergistic approach, phage cocktail, engineered phage, and anti-clustered regularly interspaced short palindromic repeats (anti-CRISPR) system. This review overwhelmingly focuses on slash the emergence of food-borne pathogens and its bacterial resistances using phage components and also discusses on the impact of phage components to diminish the outbreak of viral infections.

Bacteria utilize small signal molecules to monitor population densities. Bacteria arrange gene regulation in a method called Quorum Sensing (QS). The most widespread signalling molecules are N-Acyl Homoserine Lactones (AHLs/HSLs) for Gram-negative bacteria communities. QS plays significant role in the organizing of the bacterial gene that adapts to harsh environmental conditions for bacteria. It is involved in the arrangement of duties, such as biofilm formation occurrence, virulence activity of bacteria, production of antibiotics, plasmid conjugal transfer incident, pigmentation phenomenon and production of exopolysaccharide (EPS). QS obviously impacts on human health, agriculture and environment. AHL-related QS researches have been extensively studied and understood in depth for cell to cell intercommunication channel in Gram-negative bacteria. It is understood that AHL-based QS research has been extensively studied for cell-to-cell communication in Gram-negative bacteria; hence, a comprehensive study of AHLs, which are bacterial signal molecules, is required. The purpose of this review is to examine the effects of QS-mediated AHLs in many areas by looking at them from a different perspectives, such as clinic samples, food industry, aquatic life and wastewater treatment system.

The human body is constantly exposed to microorganisms, which entails manifold interactions between human cells and diverse commensal or pathogenic bacteria. The cellular states of the interacting cells are decisive for the outcome of these encounters such as whether bacterial virulence programmes and host defence or tolerance mechanisms are induced. This Review summarizes how next-generation RNA sequencing (RNA-seq) has become a primary technology to study host–microbe interactions with high resolution, improving our understanding of the physiological consequences and the mechanisms at play. We illustrate how the discriminatory power and sensitivity of RNA-seq helps to dissect increasingly complex cellular interactions in time and space down to the single-cell level. We also outline how future transcriptomics may answer currently open questions in host–microbe interactions and inform treatment schemes for microbial disorders. Interactions between microorganisms and their hosts are highly context dependent and contribute to both normal tissue function and infectious disease pathology. In this Review, Westermann and Vogel describe how advances in RNA sequencing techniques are providing molecular insights into host–microbe interactions, including advances in cross-species and single-cell transcriptomics.

Pseudomonas syringae pv. tabaci 6605 (Pta6605) is a causal agent of wildfire disease in host tobacco plants and is highly motile. Pta6605 has multiple clusters of chemotaxis genes including cheA, a gene encoding a histidine kinase, cheY, a gene encoding a response regulator, mcp, a gene for a methyl-accepting chemotaxis protein, as well as flagellar and pili biogenesis genes. However, only two major chemotaxis gene clusters, cluster I and cluster II, possess cheA and cheY. Deletion mutants of cheA or cheY were constructed to evaluate their possible role in Pta6605 chemotaxis and virulence. Motility tests and a chemotaxis assay to known attractant demonstrated that cheA2 and cheY2 mutants were unable to swarm and to perform chemotaxis, whereas cheA1 and cheY1 mutants retained chemotaxis ability almost equal to that of the wild-type (WT) strain. Although WT and cheY1 mutants of Pta6605 caused severe disease symptoms on host tobacco leaves, the cheA2 and cheY2 mutants did not, and symptom development with cheA1 depended on the inoculation method. These results indicate that chemotaxis genes located in cluster II are required for optimal chemotaxis and host plant infection by Pta6605 and that cluster I may partially contribute to these phenotypes.

Streptococcus suis serotype 2 (S. suis 2) is an important swine pathogen and also an emerging zoonotic agent. HtpsA has been reported as an immunogenic cell surface protein on the bacterium. In the present study, we constructed an isogenic mutant strain of htpsA, namely ΔhtpsA, to study its role in the development and virulence of S. suis 2. Our results showed that the mutant strain lost its typical encapsulated structure with decreased concentrations of sialic acid. Furthermore, the survival rate in whole blood, the anti-phagocytosis by RAW264.7 murine macrophage, and the adherence ability to HEp-2 cells were all significantly affected in the ΔhtpsA. In addition, the deletion of htpsA sharply attenuated the virulence of S. suis 2 in an infection model of mouse. RNA-seq analysis revealed that 126 genes were differentially expressed between the ΔhtpsA and the wild-type strains, including 28 upregulated and 98 downregulated genes. Among the downregulated genes, many were involved in carbohydrate metabolism and synthesis of virulence-associated factors. Taken together, htpsA was demonstrated to play a role in the morphological development and pathogenesis of the highly virulent S. suis 2 05ZYH33 strain.

In the environment, bacteria show close association, such as interspecies interaction, with other bacteria as well as host organisms. The type VI secretion system (T6SS) in gram‐negative bacteria is involved in bacterial competition or virulence. The plant pathogen Burkholderia glumae BGR1, causing bacterial panicle blight in rice, has four T6SS gene clusters. The presence of at least one T6SS gene cluster in an organism indicates its distinct role, like in the bacterial and eukaryotic cell targeting system. In this study, deletion mutants targeting four tssD genes, which encode the main component of T6SS needle formation, were constructed to functionally dissect the four T6SSs in B. glumae BGR1. We found that both T6SS group_4 and group_5, belonging to the eukaryotic targeting system, act independently as bacterial virulence factors toward host plants. In contrast, T6SS group_1 is involved in bacterial competition by exerting antibacterial effects. The Δ tssD1 mutant lost the antibacterial effect of T6SS group_1. The ΔtssD1 mutant showed similar virulence as the wild‐type BGR1 in rice because the ΔtssD1 mutant, like the wild‐type BGR1, still has key virulence factors such as toxin production towards rice. However, metagenomic analysis showed different bacterial communities in rice infected with the ΔtssD1 mutant compared to wild‐type BGR1. In particular, the T6SS group_1 controls endophytic plant‐associated bacteria such as Luteibacter and Dyella in rice plants and may have an advantage in competing with endophytic plant‐associated bacteria for settlement inside rice plants in the environment. Thus, B. glumae BGR1 causes disease using T6SSs with functionally distinct roles., T6SS group_4 and T6SS group_5 affect the pathogenicity of Burkholderia glumae BGR1 as a completely independent eukaryotic targeting system, whereas T6SS group_1 is involved in bacterial competition by an antibacterial effect.

Purpose of review The human upper respiratory tract is colonized with a variety of bacterial microorganisms including Haemophilus influenzae. The species H. influenzae consists of typeable and nontypeable H. influenzae (NTHi) variants. Typeable H. influenzae are subdivided into types a through f, based on the polysaccharide capsule, whereas the NTHi strains do not express a polysaccharide capsule. In this review, we highlight the current advances in the field of H. influenzae, with the focus on bacterial virulence mechanisms that facilitate bacterial colonization and disease, particularly for NTHi. Recent findings In the past decade, it has become apparent that NTHi has the ability to cause invasive infections. Recently, a number of adhesins have been shown to be crucial for bacterial colonization and invasion and these proteins were investigated as vaccine antigens. Although NTHi lacks a polysaccharide capsule, it expresses lipooligosaccharide that contribute to adhesion and evasion of complement-mediated killing, both contributing to bacterial virulence, which could potentially be targeted by novel antimicrobial drugs or vaccines. Summary The unraveling of H. influenzae virulence mechanisms resulted in the identification of promising targets for novel antimicrobials and vaccine antigens aiming to prevent or treat both typeable and nontypeable H. influenzae infections.

Stan Falkow looked at the world with his eyes peering from the outer membrane of a gram-negative bacterium. It was a great vantage point from which to dream about the possible superpowers these organisms might have. He mused about these dreams with his trainees who sometimes found through rigorous scientific exploration that the superpowers really were there! Stan also realized that bacterial pathogenesis by definition was a two-way street, and that masterful understanding of bacterial virulence factors also required a masterful understanding of host cell processes against which the virulence factors were deployed. In my own scientific journey, I have sought to explore bacterial-host interactions that result in subtle alterations of the host's adaptive immune response. Here, as an example, I describe an interaction between Chlamydia trachomatis and host T cells that may contribute to the establishment of persistent infection.

International audience; Porphyromonas, Tannerella, and Prevotella species found in severe periodontitis use the Type IX Secretion System (T9SS) to load their outer membrane surface with an array of virulence factors. These virulence factors are then released on outer membrane vesicles (OMVs), which penetrate the host to dysregulate the immune response to establish a positive feedback loop of chronic, inflammatory destruction of the tooth’s supporting tissues. In this review, we present the latest information on the molecular architecture of the T9SS and provide mechanistic insight into its role in secretion and attachment of cargo proteins to produce a virulence coat on cells and OMVs. The recent molecular structures of the T9SS motor comprising PorL and PorM as well as the secretion pore Sov, together with advances in the overall interactome, have provided insight into the possible mechanisms of secretion. We propose the presence of PorL/M motors arranged in a circle at the inner membrane with bent periplasmic rotors interacting with the PorN protein. At the outer membrane, we envisage a slide carousel model where the PorN protein is driven around a circular track composed of PorK. Cargo proteins are transported by PorN to PorW and the Sov translocon just as slides are rotated to the projection window. Secreted proteins are proposed to then be shuttled along highways consisting of the PorV shuttle protein to an array of attachment complexes distributed around the cell. The cell surface attachment of cargo is a hallmark of the T9SS, and in Porphyromonas gingivalis and Tannerella forsythia, this attachment is achieved via covalent bonding to a linking sugar synthesized by the Wbp/Vim pathway. The cell-surface attached cargo are enriched on OMVs, which are then released from the cell.

Streptococcus suis is a zoonotic pathogen of swine involved in arthritis, polyserositis, and meningitis. Colonization of piglets by S. suis is very common and occurs early in life. The clinical outcome of infection is influenced by the virulence of the S. suis strains and the immunity of the animals. Here, the role of innate immunity was studied in cesarean-derived colostrum-deprived piglets inoculated intranasally with either virulent S. suis strain 10 (S10) or non-virulent S. suis strain T15. Colonization of the inoculated piglets was confirmed at the end of the study by PCR and immunohistochemistry. Fever (≥40.5 °C) was more prevalent in piglets inoculated with S10 compared to T15 at 4 h after inoculation. During the 3 days of monitoring, no other major clinical signs were detected. Accordingly, only small changes in transcription of genes associated with the antibacterial innate immune response were observed at systemic sites, with S10 inducing an earlier response than T15 in blood. Local inflammatory response to the inoculation, evaluated by transcriptional analysis of selected genes in nasal swabs, was more sustained in piglets inoculated with the virulent S10, as demonstrated by transcription of inflammation-related genes, such as IL1B, IL1A, and IRF7. In contrast, most of the gene expression changes in trachea, lungs, and associated lymph nodes were observed in response to the non-virulent T15 strain. Thus, S. suis colonization in the absence of systemic infection induces an innate immune response in piglets that appears to be related to the virulence potential of the colonizing strain.

The misuses of antimicrobials in infectious diseases have led to the progress of extensive resistance in the infectious organisms. The failure of accessible antimicrobials to control infections makes it essential to discover alternatives to currently existing drugs. Their connection to infectious diseases and their natural ability to increase antimicrobial resistance in microbes, has led to platforms for research focused on new techniques to control them. Pathogenicity in many bacteria is regulated by quorum sensing (QS). Inhibition of QS system may cause reduction of virulence and protect against bacterial infections. These bacteria rely on chemical communication (or QS) to coordinate activities necessary for their survival in groups by some course of action. Their dependence on QS has made those signaling systems within bacteria an attractive target for the design of new anti-infective agents. Compounds that can interrupt these processes are known as QS inhibitors. The QS is the key regulator of virulence in various bacteria. Various plant extracts and their chemical constituents exhibited their effects on bacterial virulence factors by inhibiting QS genes and QS-controlled factors and effects on bacterial growth. The anti-QS approach is a promising one in the fight against infections pathogens, thereby making the bacteria more susceptible to traditional antimicrobials. The QS inhibitors (QSI) may provide the newest weapon against infections involving drug-resistant bacterial strains. These QSIs come from a variety of sources and have a wide array of structures.

Bacterial proteins dubbed virulence factors (VFs) are a highly diverse group of sequences, whose only obvious commonality is the very property of being, more or less directly, involved in virulence. It is therefore tempting to speculate whether their prediction, based on direct sequence similarity (seqsim) to known VFs, could be enhanced or even replaced by using machine-learning methods. Specifically, when trained on a large and diverse set of VFs, such may be able to detect putative, non-trivial characteristics shared by otherwise unrelated VF families and therefore better predict novel VFs with insignificant similarity to each individual family. We therefore first reassess the performance of dimer-based Support Vector Machines, as used in the widely used MP3 method, in light of seqsim-only and seqsim/dimer-hybrid classifiers. We then repeat the analysis with a novel, considerably more diverse data set, also addressing the important problem of negative data selection. Finally, we move on to the real-world use case of proteome-wide VF prediction, outlining different approaches to estimating specificity in this scenario. We find that direct seqsim is of unparalleled importance and therefore should always be exploited. Further, we observe strikingly low correlations between different feature and classifier types when ranking proteins by VF likeness. We therefore propose a ‘best of each world’ approach to prioritize proteins for experimental testing, focussing on the top predictions of each classifier. Further, classifiers for individual VF families should be developed.

Xanthomonas arboricola pv. juglandis is the etiologic agent of important walnut (Juglans regia L.) diseases, causing severe fruit drop and high economic losses in walnut production regions. Rapid diagnostics and knowledge of bacterial virulence fitness are key to hinder disease progression and apply timely phytosanitary measures. This work describes an X. arboricola pv. juglandis-specific real-time quantitative PCR (qPCR) using X. arboricola pv. juglandis-specific DNA markers to quantify the bacterial load in infected walnut plant tissues. Method validation was achieved using calibration curves obtained with serial dilutions of X. arboricola pv. juglandis chromosomal DNA and standard curves obtained from walnut samples spiked with X. arboricola pv. juglandis cells. High correlations (R2 > 0.990 and > 0.995) and low limits of detection (35 chromosomes/qPCR reaction and 2.7 CFU/qPCR reaction) were obtained for both markers considering the calibration and standard curves, respectively. Assessment of qPCR repeatability, reproducibility, and specificity allowed us to demonstrate the reliability and consistency of the method. Furthermore, in planta quantification of X. arboricola pv. juglandis bacterial load using infected walnut fruit samples showed a higher detection resolution compared with standard PCR detection. By allowing quantification of virulence fitness of distinct X. arboricola pv. juglandis strains in planta, the proposed qPCR method may contribute to assertive risk assessment of walnut diseases caused by X. arboricola pv. juglandis and ultimately help to improve phytosanitary practices.

The scientific review deals with the modern concepts of the quorum sensing systems LasI/R, RhlI/R, PqsABCDH/R and IQS of Pseudomonas aeruginosa bacteria, the functioning of which causes their survival under the most unfavorable and bactericidal conditions. For writing the article, information was searched ­using Scopus, Web of Science, MedLine, PubMed, Google Scholar, EMBASE, Global Health, The Cochrane Library, CyberLeninka, RISC. High antibiotic resistance of Pseudomonas aeruginosa bacteria as causative agents for nosocomial infectious diseases is due to the ability to create a biofilm. The mechanisms of biofilm formation by Pseudomonas aeruginosa bacteria, which are represented by the quorum sensing system LasI/R, RhlI/R, PqsABCDH/R and IQS, are described. The data of scientific studies that reveal the role of quorum sensing-dependent virulence factors of the bacteria Pseudomonas aeruginosa in the pathogenesis of the infectious process are presented. The hierarchical unified organization of the quorum sensing of Pseudomonas aeruginosa bacteria in the formation of a biofilm was demonstrated. The formation of biofilm by Pseudomonas aeruginosa bacteria predetermines the lack of effectiveness of antibiotic therapy and the risk of developing a chronic process. Attention is focused on the possibilities of drug suppression of quorum sensing-associated factors of bacterial virulence and biofilm formation when using any molecular component of the quorum system of sensing bacteria Pseudomonas aeruginosa as a target. The cha­racteristics of some compounds that inhibit the sensory system of Pseudomonas aeruginosa bacteria are given, and it is likely that they will be able to develop medicines for use in medical practice for the treatment of infections caused by Pseudomonas aeruginosa bacteria.

Bacterial pathogens are able to survive within diverse habitats. The dynamic adaptation to the surroundings depends on their ability to sense environmental variations and to respond in an appropriate manner. This involves, among others, the activation of various cell-to-cell communication strategies. The capability of the bacterial cells to rapidly and co-ordinately set up an interplay with the host cells and/or with other bacteria facilitates their survival in the new niche. Efflux pumps are ubiquitous transmembrane transporters, able to extrude a large set of different molecules. They are strongly implicated in antibiotic resistance since they are able to efficiently expel most of the clinically relevant antibiotics from the bacterial cytoplasm. Besides antibiotic resistance, multidrug efflux pumps take part in several important processes of bacterial cell physiology, including cell to cell communication, and contribute to increase the virulence potential of several bacterial pathogens. Here, we focus on the structural and functional role of multidrug efflux pumps belonging to the Major Facilitator Superfamily (MFS), the largest family of transporters, highlighting their involvement in the colonization of host cells, in virulence and in biofilm formation. We will offer an overview on how MFS multidrug transporters contribute to bacterial survival, adaptation and pathogenicity through the export of diverse molecules. This will be done by presenting the functions of several relevant MFS multidrug efflux pumps in human life-threatening bacterial pathogens as Staphylococcus aureus, Listeria monocytogenes, Klebsiella pneumoniae, Shigella/E. coli, Acinetobacter baumannii.

Antibiotics play a key role in the prevention and treatment of bacterial diseases for human and animals. The widespread use of antibiotics results in bacterial exposure to the concentrations that are lower than the MIC (that is, sub-inhibitory concentration (sub-MIC)) in the environment, humans, and livestock, which can lead to antibiotic resistance. In this review, we focus on the impact of sub-MIC antibiotics in bacterial virulence. This paper summarized the known relationships between sub-MIC antibiotics in the environment and bacterial virulence. Together, considering the impact of sub-MIC antibiotics and their alternative products in the virulence of bacteria, it is helpful to the rational use of antibiotics and the development of antibiotic alternative products to provide new insights.Key points• Sub-MIC level antibiotics exist in the environment, humans, and livestock.• The review includes mechanisms of sub-MIC antibiotics in bacterial virulence.• New antibacterial strategies and agents are being a new way to weaken virulence. Graphical Abstract.

Widespread methicillin-resistant Staphylococcus aureus (S. aureus) infections within community and healthcare settings are responsible for accelerated development of antibiotic resistance. As the antibiotic pipeline began drying up, alternative strategies were sought for future treatment of S. aureus infections. Here, we review immune-based anti-staphylococcal strategies that, unlike conventional antibiotics, target non-essential gene products elaborated by the pathogen. These strategies stimulate narrow or broad host immune mechanisms that are critical for anti-staphylococcal defenses. Alternative approaches aim to disrupt bacterial virulence mechanisms that enhance pathogen survival or induce immunopathology. Although immune-based therapeutics are unlikely to replace antibiotics in patient treatment in the near term, they have the potential to significantly improve upon the performance of antibiotics for treatment of invasive staphylococcal diseases.

Helicobacter pylori (H. pylori) infection is the most common cause of gastric cancer (GC). This microorganism is genetically diverse; GC is caused by several genetic deregulations in addition to environmental factors and bacterial virulence factors. lncRNAs (long noncoding RNAs) are significant biological macromolecules in GC, have specific functions in diseases, and could be therapeutic targets. Altered lncRNAs can lead to the abnormal expression of adjacent protein-coding genes, which may be important in cancer development. Their mechanisms have not been well understood, so we are going to investigate the risk of GC in a population with both high lncRNA and H. pylori infection.

The increasing prevalence of multidrug-resistant (MDR) bacterial infections has created a crucial need for new therapeutics that avoid or minimize existing resistance mechanisms. In this review, we describe the development of novel classes of small-molecule adjunctive agents targeting either a bacterial virulence factor, the Pseudomonas aeruginosa type III secretion system (T3SS), or an intrinsic resistance factor, resistance-nodulation-cell division superfamily (RND) efflux pumps of the Enterobacteriaceae. These agents are designed to be administered with antibacterials to improve their efficacy. T3SS inhibition rescues host innate immune system cells from injection with bacterial toxins, whereas RND efflux pump inhibition increases antibiotic susceptibility, in both cases improving the efficacy of the combined antibacterial.

Delivery of effectors, DNA or proteins, that hijack host cell processes to the benefit of bacteria is a mechanism widely used by bacterial pathogens. It is achieved by complex effector injection devices, the secretion systems, among which Type 4 Secretion Systems (T4SSs) play a key role in bacterial virulence of numerous animal and plant pathogens. Considerable progress has recently been made in the structure-function analyses of T4SSs. Nevertheless, the signals and processes that trigger machine assembly and activity during infection, as well as those involved in substrate recognition and transfer, are complex and still poorly understood. In this review, we aim at summarizing the last updates of the knowledge on signaling pathways that regulate the biogenesis and the activity of T4SSs in important bacterial pathogens.

Campylobacter jejuniis a predominant zoonotic pathogen causing gastroenteritis and other diseases in humans. An important bacterial virulence factor is the secreted serine protease HtrA (HtrA(Cj)), which targets tight and adherens junctional proteins in the gut epithelium. Here we have investigated the function and structure of HtrA(Cj)using biochemical assays and cryo-electron microscopy. Mass spectrometry analysis identified differences and similarities in the cleavage site specificity for HtrA(Cj)by comparison to the HtrA counterparts fromHelicobacter pyloriandEscherichia coli. We defined the architecture of HtrA(Cj)at 5.8 angstrom resolution as a dodecamer, built of four trimers. The contacts between the trimers are quite loose, a fact that explains the flexibility and mobility of the dodecameric assembly. This flexibility has also been studied through molecular dynamics simulation, which revealed opening of the dodecamer to expose the proteolytically active site of the protease. Moreover, we examined the rearrangements at the level of oligomerization in the presence or absence of substrate using size exclusion chromatography, which revealed hexamers, dodecamers and larger oligomeric forms, as well as remarkable stability of higher oligomeric forms (> 12-mers) compared to previously tested homologs from other bacteria. Extremely dynamic decay of the higher oligomeric forms into lower forms was observed after full cleavage of the substrate by the proteolytically active variant of HtrA(Cj). Together, this is the first report on the in-depth functional and structural analysis of HtrA(Cj), which may allow the construction of therapeutically relevant HtrA(Cj)inhibitors in the near future.

Piscirickettsia salmonis is the causative agent of Piscirickettsiosis, an infectious disease with a high economic impact on the Chilean salmonid aquaculture industry. This bacterium produces biofilm as a potential resistance and persistence strategy against stressful environmental stimuli. However, the in vitro culture conditions that modulate biofilm formation as well as the effect of sessile bacteria on virulence and immune gene expression in host cells have not been described for P. salmonis. Therefore, this study aimed to analyze the biofilm formation by P. salmonis isolates under several NaCl and iron concentrations and to evaluate the virulence of planktonic and sessile bacteria, together with the immune gene expression induced by these bacterial conditions in an Atlantic salmon macrophage cell line. Our results showed that NaCl and Fe significantly increased biofilm production in the LF-89 type strain and EM-90-like isolates. Additionally, the planktonic EM-90 isolate and sessile LF-89 generated the highest virulence levels, associated with differential expression of il-1&beta, il-8, nf-&kappa, b, and i&kappa, b-&alpha, genes in SHK-1 cells. These results suggest that there is no single virulence pattern or gene expression profile induced by the planktonic or sessile condition of P. salmonis, which are dependent on each strain and bacterial condition used.

Virulent strains of Streptococcus pyogenes (gram-positive group A Streptococcus pyogenes [GAS]) recruit host single-chain human plasminogen (hPg) to the cell surface—where in the case of Pattern D strains of GAS, hPg binds directly to the cells through a surface receptor, plasminogen-binding group A streptococcal M-protein (PAM). The coinherited Pattern D GAS-secreted streptokinase (SK2b) then accelerates cleavage of hPg at the R561-V562 peptide bond, resulting in the disulfide-linked two-chain protease, human plasmin (hPm). hPm localizes on the bacterial surface, assisting bacterial dissemination via proteolysis of host defense proteins. Studies using isolated domains from PAM and hPg revealed that the A-domain of PAM binds to the hPg kringle-2 module (K2hPg), but how this relates to the function of the full-length proteins is unclear. Herein, we use intact proteins to show that the lysine-binding site of K2hPg is a major determinant of the activation-resistant T-conformation of hPg. The binding of PAM to the lysine-binding site of K2hPg relaxes the conformation of hPg, leading to a greatly enhanced activation rate of hPg by SK2b. Domain swapping between hPg and mouse Pg emphasizes the importance of the Pg latent heavy chain (residues 1–561) in PAM binding and shows that while SK2b binds to both hPg and mouse Pg, the activation properties of streptokinase are strictly attributed to the serine protease domain (residues 562–791) of hPg. Overall, these data show that native hPg is locked in an activation-resistant conformation that is relaxed upon its direct binding to PAM, allowing hPm to form and provide GAS cells with a proteolytic surface.

The Gram-negative opportunistic pathogen Acinetobacter baumannii has gain notoriety in recent decades, primarily due to its propensity to cause nosocomial infections in critically ill patients. Its global spread, multi-drug resistance features and plethora of virulence factors make it a serious threat to public health worldwide. Though much effort has been expended in uncovering its successes, it continues to confound researchers due to its highly adaptive nature, mutating to meet the needs of a given environment. Its persistence in the clinical setting allows it to be in close proximity to a potential host, where contact can be made facilitating infection and colonization. In this article, we aim to provide a current overview of the bacterial virulence factors, specifically focusing on factors involved in the initial stages of infection, highlighting the role of adaptation facilitated by two-component systems and biofilm formation. Finally, the study of host-pathogen interactions using available animal models, their suitability, notable findings and some perspectives moving forward are also discussed.

Despite its potential importance for bacterial virulence, protein rhamnosylation has not yet been sufficiently studied. Specific anti-SerRha, anti-ThrRha and anti-AsnRha antibodies allowed the identification of previously unknown monorhamnosylated proteins in cytosol and membrane fractions of bacterial cell lysates. Mapping of the complete rhamnoproteome in pathogens should facilitate development of targeted therapies against bacterial infections.

Pseudomonas aeruginosa is the most common human opportunistic pathogen associated with nosocomial diseases. In 2017, the World Health Organization has classified P. aeruginosa as a critical agent threatening human health, and for which the development of new treatments is urgently necessary. One interesting avenue is to target virulence factors to understand P. aeruginosa pathogenicity. Thus, characterising exoproteins of P. aeruginosa is a hot research topic and proteomics is a powerful approach that provides important information to gain insights on bacterial virulence. The aim of this review is to focus on the contribution of proteomics to the studies of P. aeruginosa exoproteins, highlighting its relevance in the discovery of virulence factors, post-translational modifications on exoproteins and host-pathogen relationships.

The advent of inexpensive and rapid sequencing technologies has allowed bacterial whole-genome sequences to be generated at an unprecedented pace. This wealth of information has revealed an unanticipated degree of strain-to-strain genetic diversity within many bacterial species. Awareness of this genetic heterogeneity has corresponded with a greater appreciation of intra-species variation in virulence. A number of comparative genomic strategies have been developed to link these genotypic and pathogenic differences with the aim of discovering novel virulence factors. Here, we review recent advances in comparative genomic approaches to identify bacterial virulence determinants, with a focus on genome-wide association studies and machine learning.

The 1940s and 1950s witnessed a diverse search for not just natural product antibiotics but also for synthetic and semisynthetic compounds. This review revisits this epoch, using the research by a Danish pharmaceutical company, LEO Pharma, as an example. LEO adopted a strategy searching for synthetic antibiotics toward specific bacterial pathogens, in particular Mycobacterium tuberculosis, leading to the discovery of a new derivative of a known drug. Work on penicillin during and after WWII lead to the development of associated salts/esters and a search for new natural product antibiotics. This led initially to no new, marketable compounds, but concluded with the serendipitous discovery of fusidic acid, an antibiotic used to treat infections by Staphylococcus aureus, in 1960. The discovery process included contemporary approaches such as open innovation; targeting specific pathogens and/or specific organs in the patient; examining the effects of antimicrobial compounds on bacterial virulence as well as on antibiotic-resistant variants, and searching for antibiotic producers among microorganisms not previously well explored. These activities were promoted by the collaboration with a renowned Danish clinical microbiologist, K. A. Jensen, as well as company expertise in fermentation technologies, chemical synthesis and purification of bioactive compounds from organic materials.

Bacterial membrane vesicles (MVs) mediate bacterial virulence by enabling secretion and long distance delivery of bacterial effector molecules. Staphylococcus haemolyticus has now been demonstrated to produce membrane vesicles (MVs). The protein content of S. haemolyticus MVs was identified by Mass spectrometry and compared to proteins identified in the total secretome. This information is presented in this data article. Further background and interpretation of the data can be found in the article: Comparative exoproteome profiling of an invasive and a commensal S. haemolyticus isolate (Cavanagh et al., in press). Data are available via Proteome Xchange with identifier PXD010389.

A large body of literature has established the link between periodontal disease and cardiovascular disease. Oxidized low-density lipoproteins (OxLDLs) have a crucial role in atherosclerosis progression through initiation of immunological response. Monoclonal IgM antibodies to malondialdehyde-modified low-density lipoprotein (MDA-LDL) and to malondialdehyde acetaldehyde–modified low-density lipoprotein (MAA-LDL) have been shown to cross-react with the key virulence factors of periodontal pathogens Porphyromonas gingivalis and Aggregatibacter actinomycetemcomitans. We have previously shown that salivary IgA antibodies to MAA-LDL cross-react with P. gingivalis in healthy humans. In this study, we aim to assess whether oral mucosal immune response represented by salivary IgA to MAA-LDL and oral pathogens is associated with coronary artery disease (CAD). Also, the molecular mimicry through antibody cross-reaction between salivary IgA to MAA-LDL and oral pathogens was evaluated. The study subjects consisted of 451 patients who underwent a coronary angiography with no CAD ( n = 133), stable CAD ( n = 169), and acute coronary syndrome (ACS, n = 149). Elevated salivary IgA antibody levels to MAA-LDL, Rgp44 (gingipain A hemagglutinin domain of P. gingivalis), and Aa-HSP60 (heat shock protein 60 of A. actinomycetemcomitans) were discovered in stable-CAD and ACS patients when compared to no-CAD patients. In a multinomial regression model adjusted for known cardiovascular risk factors, stable CAD and ACS were associated with IgA to MAA-LDL ( P = 0.016, P = 0.043), Rgp44 ( P = 0.012, P = 0.004), Aa-HSP60 ( P = 0.032, P = 0.030), Tannerella forsythia ( P = 0.002, P = 0.004), Porphyromonas endodontalis ( P = 0.016, P = 0.020), Prevotella intermedia ( P = 0.038, P = 0.005), and with total IgA antibody concentration ( P = 0.002, P = 0.016). Salivary IgA to MAA-LDL showed cross-reactivity with the oral pathogens tested in the study patients. The study highlights an association between salivary IgA to MAA-LDL and atherosclerosis. However, whether salivary IgA to MAA-LDL and the related oral humoral responses play a causal role in the development in the CAD should be elucidated in the future.

This paper describes urinary tract infections (UTI) from the perspective of a disturbed balance between bacterial virulence and host defence. In some children, a UTI is caused by a virulent Escherichia coli, while in other cases children with abnormal renal tracts can get infected by almost any bacteria. Such knowledge can help in guiding treatment, investigations and follow-up of a child with a UTI.

The prevalence of Pseudomonas syringae pv. porri (Pspo) in Belgium continues to increase and sustainable treatments for this pathogen remain unavailable. A potentially attractive biocontrol strategy would be the application of bacteriophages. The ideal application strategy of phages in an agricultural setting remains unclear, especially in a field-based production such as for leek plants in Flanders. Therefore, more insight in bacteria&ndash, phage interaction is required, along with the evaluation of different application strategies. In this study, we further characterized the infection strategy of two Pspo phages, KIL3b and KIL5. We found that both phages recognize lipopolysaccharide (LPS) moieties on the surface of the bacterium. LPS is an important pathogenicity factor of Pspo. Our data also suggest that KIL5 requires an additional protein in the bacterial cytoplasmatic membrane to efficiently infect its host. Virulence tests showed that this protein also contributes to Pspo virulence. Furthermore, a cocktail of both phages was applied in a seed bioassay. A combination of KIL3b and KIL5 reduced the bacterial concentration 100-fold. However, in vitro Pspo resistance against phage infection developed quite rapidly. However, the impact of this phage resistance might be mitigated as is suggested by the fact that those resistance mutations preferably occur in genes involved in LPS metabolism, and that the virulence of those mutants is possibly reduced. Our data suggest that the phage cocktail has promising potential to lower the prevalence of Pspo and to be integrated in a pest management strategy. Targeted research is needed to further explore the applicability of the phages in combination with other disease control strategies.

International audience; Secretion systems are employed by bacteria to transport macromolecules across membranes without compromising their integrities. Processes including virulence, colonization, and motility are highly dependent on the secretion of effector molecules toward the immediate cellular environment, and in some cases, into the host cytoplasm. In Type II and Type III secretion systems, as well as in Type IV pili, homomultimeric complexes known as secretins form large pores in the outer bacterial membrane, and the localization and assembly of such 1 MDa molecules often relies on pilotins or accessory proteins. Significant progress has been made toward understanding details of interactions between secretins and their partner proteins using approaches ranging from bacterial genetics to cryo electron microscopy. This review provides an overview of the mode of action of pilotins and accessory proteins for T2SS, T3SS, and T4PS secretins, highlighting recent near-atomic resolution cryo-EM secretin complex structures and underlining the importance of these interactions for secretin functionality.

Bacterial infections have been traditionally controlled by antibiotics and vaccines, and these approaches have greatly improved health and longevity. However, multiple stakeholders are declaring that the lack of new interventions is putting our ability to prevent and treat bacterial infections at risk. Vaccine and antibiotic approaches still have the potential to address this threat. Innovative vaccine technologies, such as reverse vaccinology, novel adjuvants, and rationally designed bacterial outer membrane vesicles, together with progress in polysaccharide conjugation and antigen design, have the potential to boost the development of vaccines targeting several classes of multidrug-resistant bacteria. Furthermore, new approaches to deliver small-molecule antibacterials into bacteria, such as hijacking active uptake pathways and potentiator approaches, along with a focus on alternative modalities, such as targeting host factors, blocking bacterial virulence factors, monoclonal antibodies, and microbiome interventions, all have potential. Both vaccines and antibacterial approaches are needed to tackle the global challenge of antimicrobial resistance (AMR), and both areas have the underpinning science to address this need. However, a concerted research agenda and rethinking of the value society puts on interventions that save lives, by preventing or treating life-threatening bacterial infections, are needed to bring these ideas to fruition.

New classes of antimicrobials that are effective therapies for infections with multi-drug resistant pathogens are urgently needed. The nematode Caenorhabditis elegans has been incorporated into small molecule screening platforms to identify anti-infective compounds that provide protection of a host during infection. The use of a live animal in these screening systems offers several advantages, including the ability to identify molecules that boost innate immune responses in a manner advantageous to host survival and compounds that disrupt bacterial virulence mechanisms. In addition, new classes of antimicrobials that target the pathogen have been uncovered, as well as interesting chemical probes that can be used to dissect new mechanisms of host-pathogen interactions.

The glyoxylate shunt bypasses the oxidative decarboxylation steps of the tricarboxylic acid (TCA) cycle, thereby conserving carbon skeletons for gluconeogenesis and biomass production. In Escherichia coli, carbon flux is redirected through the first enzyme of the glyoxylate shunt, isocitrate lyase (ICL), following phosphorylation and inactivation of the TCA cycle enzyme, isocitrate dehydrogenase (ICD), by the kinase/phosphatase, AceK. In contrast, mycobacterial species lack AceK and employ a phosphorylation-insensitive isocitrate dehydrogenase (IDH), which is allosterically activated by the product of ICL activity, glyoxylate. However, Pseudomonas aeruginosa expresses IDH, ICD, ICL, and AceK, raising the question of how these enzymes are regulated to ensure proper flux distribution between the competing pathways. Here, we present the structure, kinetics, and regulation of ICL, IDH, and ICD from P. aeruginosa. We found that flux partitioning is coordinated through reciprocal regulation of these enzymes, linking distribution of carbon flux to the availability of the key gluconeogenic precursors, oxaloacetate and pyruvate. Specifically, a greater abundance of these metabolites activated IDH and inhibited ICL, leading to increased TCA cycle flux. Regulation was also exerted through AceK-dependent phosphorylation of ICD; high levels of acetyl-CoA (which would be expected to accumulate when oxaloacetate is limiting) stimulated the kinase activity of AceK, whereas high levels of oxaloacetate stimulated its phosphatase activity. In summary, the TCA cycle–glyoxylate shunt branch point in P. aeruginosa has a complex enzymology that is profoundly different from those in other species characterized to date. Presumably, this reflects its predilection for consuming fatty acids, especially during infection scenarios.

International audience; AbstractThe alarming number of recently reported human illnesses with bacterial infections resistant to multiple antibacterial agents has become a serious concern in recent years. This phenomenon is a core challenge for both the medical and animal health communities, since the use of antibiotics has formed the cornerstone of modern medicine for treating bacterial infections. The empirical benefits of using antibiotics to address animal health issues in animal agriculture (using therapeutic doses) and increasing the overall productivity of animals (using sub-therapeutic doses) are well established. The use of antibiotics to enhance profitability margins in the animal production industry is still practiced worldwide. Although many technical and economic reasons gave rise to these practices, the continued emergence of antimicrobial resistant bacteria is furthering the need to reduce the use of medically important antibiotics. This will require improving on-farm management and biosecurity practices, and the development of effective antibiotic alternatives that will reduce the dependence on antibiotics within the animal industry in the foreseeable future. A number of approaches are being closely scrutinized and optimized to achieve this goal, including the development of promising antibiotic alternatives to control bacterial virulence through quorum-sensing disruption, the use of synthetic polymers and nanoparticles, the exploitation of recombinant enzymes/proteins (such as glucose oxidases, alkaline phosphatases and proteases), and the use of phytochemicals. This review explores the most recent approaches within this context and provides a summary of practical mitigation strategies for the extensive use of antibiotics within the animal production chain in addition to several future challenges that need to be addressed.

Bacterial biofilms remain a persistent threat to human health-care due to their role in the development of antimicrobial resistance. To combat multi-drug resistant pathogens, it is crucial to enhance our understanding of not only the regulation of biofilm formation, but also its contribution to bacterial virulence. Iron acquisition lies at the crux of these two subjects. In this review, we discuss the role of iron acquisition in biofilm formation and how hosts impede this mechanism to defend against pathogens. We also discuss recent findings that suggest that biofilm formation can also have the reciprocal effect, influencing siderophore production and iron sequestration.

Transition metals are required cofactors for many proteins that are critical for life, and their concentration within cells is carefully maintained to avoid both deficiency and toxicity. To defend against bacterial pathogens, vertebrate immune proteins sequester metals, in particular zinc, iron, and manganese, as a strategy to limit bacterial acquisition of these necessary nutrients in a process termed “nutritional immunity.” In response, bacteria have evolved elegant strategies to access metals and counteract this host defense. In mammals, metal abundance can drastically shift due to changes in dietary intake or absorption from the intestinal tract, disrupting the balance between host and pathogen in the fight for metals and altering susceptibility to disease. This review describes the current understanding of how dietary metals modulate host-microbe interactions and the subsequent impact on the outcome of disease.

Metal acquisition is vital to pathogens for successful infection within hosts. Staphylopine (StP), a broad-spectrum metallophore biosynthesized by the major human pathogen, Staphylococcus aureus, plays a central role in transition-metal acquisition and bacterial virulence. The StP-like biosynthesis loci are present in various pathogens, and the proteins responsible for StP/metal transportation have been determined. However, the molecular mechanisms of how StP/metal complexes are recognized and transported remain unknown. We report multiple structures of the extracytoplasmic solute-binding protein CntA from the StP/metal transportation system in apo form and in complex with StP and three different metals. We elucidated a sophisticated metal-bound StP recognition mechanism and determined that StP/metal binding triggers a notable interdomain conformational change in CntA. Furthermore, CRISPR/Cas9-mediated single-base substitution mutations and biochemical analysis highlight the importance of StP/metal recognition for StP/metal acquisition. These discoveries provide critical insights into the study of novel metal-acquisition mechanisms in microbes.

Whole-genome analysis of Mycobacterium tuberculosis isolates collected in Russia (N = 71) from patients with tuberculous spondylitis supports a detailed characterization of pathogen strain distributions and drug resistance phenotype, plus distinguished occurrence and association of known resistance mutations. We identify known and novel genome determinants related to bacterial virulence, pathogenicity, and drug resistance.

The aim of the study was to determine the prevalence of virulence genes responsible for the adhesion (flaA, cadF and racR) and invasion (virB11, iam and pldA) in Campylobacter isolates from cattle and swine and determine their adherence and invasion abilities. The studies conducted revealed high prevalence rate of adherence and invasion associated genes irrespective of the isolates origin. All Campylobacter strains of swine and cattle origin adhered to HeLa cells at mean level 0.1099% ± SD 0.1341% and 0.0845% ± SD 0.1304% of starting viable inoculum, respectively. However swine isolates exhibited higher invasion abilities (0.0012% ± SD 0.0011%) compared to bovine isolates (0.00038% ± SD 0.00055%). The results obtained revealed significantly positive correlation between invasion and adherence abilities of swine origin isolates (R = 0.4867 in regard to C. jejuni and R = 0.4507 in regard to C. coli) and bovine origin isolates (R = 0.726 in regard to C. jejuni). Bacterial virulence is multifactorial and it is affected by the expression of virulence genes. Moreover the presence of virulence genes determines the ability of Campylobacter isolates to adhere and invade the cells.

With prompt administration of appropriate antimicrobial therapy and access to modern intensive care support, fatal pediatric melioidosis is very unusual. We describe cases of two children in whom the possibility of melioidosis was recognized relatively early, but who died of the disease, despite receiving optimal supportive care. We discuss the resulting implications for bacterial virulence factors in disease pathogenesis.

Methylation of outer membrane proteins (OMPs) has been implicated in bacterial virulence. Lysine methylation in rickettsial OmpB is correlated with rickettsial virulence, and N- and O-methylations are also observed in virulence-relevant OMPs from several pathogenic bacteria that cause typhus, leptospirosis, tuberculosis, and anaplasmosis. We summarize recent findings on the structure of methylated OmpB, biochemical characterization, and crystal structures of OmpB methyltransferases. Native rickettsial OmpB purified from highly virulent strains contains multiple clusters of trimethyllysine, in contrast with mostly monomethyllysine, and no trimethyllysine is found in an avirulent strain. Crystal structure of the methyltransferases reveals mechanistic insights for catalysis, and a working model is discussed for this unusual post-translational modification.

This research set out to identify compounds from marine sponges that can act as bacterial virulence blockers. Extracts from a total of 80 sponges collected from throughout Indonesia were screened in a high-throughput NF-κB-based screen that identifies compounds capable of inhibiting the bacterial type III secretion system (T3SS) in Yersinia pseudotuberculosis. An extract that was shown to inhibit T3SS-driven NF-κB expression was obtained from an Iotrochota cf. iota sponge and was the source of seven new bromo- and iodo-containing compounds, all of which contain a 2-(4-oxyphenyl)ethan-1-amine core. Five were determined to be new compounds and named enisorines A-E (1-5). The remaining two were determined to be new hemibastadinol analogues named (+)-1-O-methylhemibastadinol 2 (6) and (+)-1-O-methylhemibastadinol 4 (7). All seven compounds inhibited T3SS-dependent YopE secretion and did not affect the growth or metabolic activity of Y. pseudotuberculosis. The most potent inhibitors of T3SS activity were enisorine C (3), enisorine E (5), and (+)-1-O-methylhemibastadinol 2 (6), all of which inhibited YopE secretion by50% at 30 μM.

The present study has examined the virulence potential of Escherichia coli isolates harboring at least one virulence gene (associated with ExPEC or InPEC pathotype and belonging to different phylogenetic groups: A, B1, B2 or D), isolated from free ranging Tibetan yak feces. The E. coli isolates (n = 87) were characterized for different serogroups and a mouse model of subcutaneous–infection was used to envisage the virulence within these E. coli strains. Of the 87 E. coli isolates examined, 23% of the E. coli isolates caused lethal infections in a mouse model of subcutaneous infection and were classified as killer. Moreover, the majority of the killer strains belonged to phylogroup A (65%) and serogroup O60 or O101 (35%). Phylogroup B1, serogroups O60 and O101 were statistically associated with the killer status (P 1) were observed between the killer status isolates and all other bacterial virulence traits. This study comprises the first report on the virulence potential of E. coli strains isolated from free-ranging Tibetan yaks feces. Our findings suggest that pathogenic E. coli of free ranging yaks is highly worrisome, as these feces are used as manures by farmers and therewith pose a health risk to humans upon exposure.

The bacterial communication through signaling molecules termed quorum sensing has gained a lot of attention due to its applicability to different fields of study. Quorum sensing regulates several bacterial activities such as biofilm formation, antibiotic resistance, bioluminescence and bacterial virulence. These coordinated activities are only realized when the bacterial population reaches a high population density. The signaling molecules used in quorum sensing occur at very low concentrations which call for very sensitive methods for their identification and characterization. Many studies have been performed on the use of inhibitors in attempt to disrupt quorum sensing and consequently alleviate its negative effects. This article gives a description of the types of auto-inducers involved in quorum sensing and the fields of study they greatly affect especially the environmental one. It also covers types of analytical sample preparation and detection methods, and different types of inhibitors used for quorum quenching.

The continued rise of antibiotic-resistant bacterial infections has motivated alternative strategies for target discovery and treatment of infections. Antivirulence therapies function through inhibition of in vivo required virulence factors to disarm the pathogen instead of directly targeting viability or growth. This approach to treating bacteria-mediated diseases may have advantages over traditional antibiotics because it targets factors specific for pathogenesis, potentially reducing selection for resistance and limiting collateral damage to the resident microbiota. This review examines vulnerable molecular mechanisms used by bacteria to cause disease and the antivirulence compounds that sabotage these virulence pathways. By expanding the study of antimicrobial targets beyond those that are essential for growth, antivirulence strategies offer new and innovative opportunities to combat infectious diseases.

Silver (Ag) has been gaining broad attention due to their antimicrobial activities and the increasing resistance of bacteria to commonly prescribed antibiotics. However, various aspects of the antimicrobial mechanism of Ag have not been understood, including how silver affects the motility of bacteria, a factor that is intimately related to bacterial virulence. Here we report our study on the antibiotic effects of Ag+ions on the motility ofE. colibacteria using swimming and tethering assays. We observed that the bacteria slowed down dramatically when subjected to Ag+ions, providing direct evidence showing that Ag inhibits the motility of bacteria. In addition, through tethering assays, we monitored the rotation of flagellar motors and observed that the tumbling frequency of bacteria increased significantly in the presence of Ag+ions. Furthermore, the rotation of bacteria in the tethering assays were analyzed using hidden Markov model (HMM); and we found that Ag+-treatment led to a significant decrease in the tumbling-to-running transition rate of the bacteria, suggesting that the rotation of bacterial flagellar motors was stalled by Ag+ions. This work provided a new quantitative understanding on the mechanism of Ag-based antimicrobial agents in bacterial motility.