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The strict human pathogen

INTRODUCTION/BACKGROUND: Glioblastoma multiforme show constitutive activation of cyclin-dependent kinases (CDKs) or arginine auxotrophy. This renders tumor cells vulnerable towards arginine-depleting substances, such as arginine deiminase from Streptococcus pyogenes (SpyADI). Previously, we confirmed the susceptibility of patient-derived GBM cells towards administration of SpyADI as well as CDK inhibitors (CDKis). To improve effects, we applied a sequential (SEQ) CDKi/SpyADI approach to examine mechanistic insights and drug susceptibility. MATERIALS AND METHODS: Three arginine-auxotrophic patient-derived GBM lines with different molecular characteristics were cultured in 2D and 3D (spheres and glioma stem-like cells (GSC)) and effects of this combined CDKi/SpyADI approach were analyzed. This included viability staining via Calcein AM in 2D and 3D-Glo in 3D culture and cell death analysis via flow cytometry. Therapy-induced morphological changes were identified with transmission electron microscopy (TEM). Besides, 3D-invasiveness, cellular stress, and DNA damage responses were measured. RESULTS: All SEQ-CDKi/SpyADI combinations yielded synergistic antitumoral effects, characterized by impaired cell proliferation, invasiveness, and viability. Notably, this SEQ-CDKi/SpyADI approach was most effective in 3D models. Mitochondrial impairment was demonstrated by increasing mitochondrial membrane potential and decreasing oxygen consumption rate along with extracellular acidification rate after abemaciclib/SpyADI monotherapy or its combination regimens. TEM confirmed damaged mitochondria and endoplasmic reticulum together with increased vacuolization under CDKi mono- and SEQ- CDKi/SpyADI combination therapy. SEQ-abemaciclib/SpyADI treatment suppressed the DSB repair system via NHEJ and HR, whereas SEQ-dinaciclib/SpyADI treatment increased γ-H2AX accumulation and induced Rad51/Ku80. The latter combination also activated the stress sensor GADD45 and β-catenin antagonist AXIN2. CONCLUSION: This study highlights the antitumoral potential of a combined SpyADI/CDKi approach. We show that sequential application of these substances has complex effects on mitochondrial dysfunction, invasiveness, and DNA-damage response. This provides a good starting point for further proof-of-concept studies to move forward with this strategy.

Lactic acid bacteria (LAB) play a significant role in biotechnology, e.g. food industry, but also in human health. Many LAB genera have developed a multidrug resistance in the past few years, becoming a serious problem in controlling hospital germs all around the world. Enterococcus faecalis accounts for a large part of the human infections caused by LABs. Therefore, studying its adaptive metabolism under various environmental conditions is particularly important. In this study, we investigated the effect of glutamine auxotrophy (ΔglnA mutant) on metabolic and proteomic adaptations of E. faecalis in response to a changing pH in its environment. Changing pH values are part of its natural environment in the human body, but also play a role in food industry. We compared the results to those of the wildtype. Our integrative method, using a genome-scale metabolic model, constrained by metabolic and proteomic data allows us to understand the bigger picture of adaptation strategies in this bacterium. The study showed that energy demand is the decisive factor in adapting to a new environmental pH. The energy demand of the mutant was higher at all conditions. It has been reported that ΔglnA mutants of bacteria are energetically less effective. With the aid of our data and model we are able to explain this phenomenon as a consequence of a failure to regulate glutamine uptake and the costs for the import of glutamine and the export of ammonium. Methodologically, it became apparent that taking into account the non-specificity of amino acid transporters is important for reproducing metabolic changes with genome-scale models since it affects energy balance.

In-depth understanding of microbial growth is crucial for the development of new advances in biotechnology and for combating microbial pathogens. Condition-specific proteome expression is central to microbial physiology and growth. A multitude of processes are dependent on the protein expression, thus, whole-cell analysis of microbial metabolism using genome-scale metabolic models is an attractive toolset to investigate the behaviour of microorganisms and their communities. However, genome-scale models that incorporate macromolecular expression are still inhibitory complex: the conceptual and computational complexity of these models severely limits their potential applications. In the need for alternatives, here we revisit some of the previous attempts to create genome-scale models of metabolism and macromolecular expression to develop a novel framework for integrating protein abundance and turnover costs to conventional genome-scale models. We show that such a model of Escherichia coli successfully reproduces experimentally determined adaptations of metabolism in a growth condition-dependent manner. Moreover, the model can be used as means of investigating underutilization of the protein machinery among different growth settings. Notably, we obtained strongly improved predictions of flux distributions, considering the costs of protein translation explicitly. This finding in turn suggests protein translation being the main regulation hub for cellular growth.

In aseptic loosening of endoprosthetic implants, metal particles, as well as their corrosion products, have been shown to elicit a biological response. Due to different metal alloy components, the response may vary depending on the nature of the released corrosion product. Our study aimed to compare the biological effects of different ions released from metal alloys. In order to mimic the corrosion products, different metal salts (CoCl2, NiCl2 and CrCl3 × 6H2O) were dissolved and allowed to equilibrate. Human osteoblasts were incubated with concentrations of 10 µM to 500 µM metal salt solutions under cell culture conditions, whereas untreated cells served as negative controls. Cells exposed to CoCr28Mo6 particles served as positive controls. The cell activity and expression of osteogenic differentiation and pro-osteolytic mediators were determined. Osteoblastic activity revealed concentration- and material-dependent influences. Collagen 1 synthesis was reduced after treatment with Co(2+) and Ni(2+). Additionally, exposure to these ions (500 µM) resulted in significantly reduced OPG protein synthesis, whereas RANKL as well as IL-6 and IL-8 secretion were increased. TLR4 mRNA was significantly induced by Co(2+) and CoCr28Mo6 particles. The results demonstrate the pro-osteolytic capacity of metal ions in osteoblasts. Compared to CoCr28Mo6 particles, the results indicated that metal ions intervene much earlier in inflammatory processes.

Arginine auxotrophy occurs in certain tumor types and is usually caused by the silencing of argininosuccinate synthetase 1 or arginine lyase genes. Such tumors are often associated with an intrinsic chemoresistance and thus a poor prognosis. Arginine auxotrophy however renders these tumors vulnerable to treatment with arginine-degrading enzymes. Among the most frequently applied arginine-degrading agents are bacterial arginine deiminases (ADI). The anti-cancerous effects of ADI derived from different bacteria were extensively studied in numerous preclinical cell culture and xenograft models. Mycoplasma-derived ADI-PEG20 is most commonly used and is currently under clinical investigation as a single agent therapeutic as well as in combination with different antineoplastic compounds. Mechanistically, ADI is capable of reducing metabolic activity in tumor cells, contributing to autophagy, senescence and apoptosis in arginine auxotrophic cells. Although clinical trials are promising, the resistance development upon initial treatment response is an increasing challenge. Furthermore, interference of ADI with the tumor microenvironment is poorly understood. In the present review, we outline recent experimental ADI-based treatment approaches and their translation into the clinic. Furthermore, we summarize new insights into the molecular mechanisms underlying the anti-cancer effects of ADI that might facilitate the refinement of ADI-based combination therapy approaches.

Arginine auxotrophy constitutes a weak point of several tumors, among them glioblastoma multiforme (GBM). Hence, those tumors are supposed to be sensitive for arginine-depleting substances, such as arginine deiminase (ADI). Here we elucidated the sensitivity of patient-individual GBM cell lines toward Streptococcus pyogenes-derived ADI. To improve therapy, ADI was combined with currently established and pre-clinical cytostatic drugs. Additionally, effectiveness of local ADI therapy was determined in xenopatients. Half of the GBM cell lines tested responded well toward ADI monotherapy. In those cell lines, viability decreased significantly (up to 50 %). Responding cell lines were subjected to combination therapy experiments to test if any additive or even synergistic effects may be achieved. Such promising results were obtained in 2/3 cases. In cell lines HROG02, HROG05 and HROG10, ADI and Palomid 529 combinations were most effective yielding more than 70 % killing after 2 rounds of treatment. Comparable boosted antitumoral effects were observed after adding chloroquine to ADI (>60% killing). Apoptosis, as well as cell cycle dysregulation were found to play a minor role. In some, but clearly not all cases, (epi-) genetic silencing of arginine synthesis pathway genes (argininosuccinate synthetase 1 and argininosuccinate lyase) explained obtained results. In vivo, ADI as well as the combination of ADI and SAHA efficiently controlled HROG05 xenograft growth, whereas adding Palomid 529 to ADI did not further increase the strong antitumoral effect of ADI. The cumulative in vitro and in vivo results proved ADI as a very promising candidate therapeutic, especially for development of adjuvant GBM combination treatments.

Streptococcus pyogenes uses lactic acid fermentation for the generation of ATP. Here, we analyzed the impact of a deletion of the L-lactate dehydrogenase gene ldh on the virulence of S. pyogenes M49. While the ldh deletion does not cause a general growth deficiency in laboratory media, the growth in human blood and plasma is significantly hampered. The ldh deletion strain is furthermore less virulent in a Galleria mellonella infection model. We show that the ldh deletion leads to a decrease in the activity of the cysteine protease SpeB, an important secreted virulence factor of S. pyogenes. The reduced SpeB activity is caused by a hampered autocatalytic activation of the SpeB zymogen into the mature SpeB. The missing SpeB activity furthermore leads to increased plasmin activation and a reduced activation of the contact system on the surface of S. pyogenes. All these effects can be reversed when ldh is reintroduced into the mutant via a plasmid. The results demonstrate a previously unappreciated role for LDH in modulation of SpeB maturation.

Arginine auxotrophy constitutes the Achilles' heel for several tumors, among them glioblastoma multiforme (GBM). Hence, arginine-depleting enzymes such as arginine deiminase (ADI) from Streptococcus pyogenes are promising for treatment of primary and maybe even refractory GBM. Based on our previous study in which ADI-susceptibility was shown on a panel of patient-derived GBM cell lines, we here aimed at deciphering underlying molecular mechanisms of ADI-mediated growth inhibition. We found that ADI (35 mU/mL) initially induces a cellular stress-response that is characterized by upregulation of genes primarily belonging to the heat-shock protein family. In addition to autophagocytosis, we show for the first time that senescence constitutes another cellular response mechanism upon ADI-treatment and that this bacterial enzyme is able to act as radiosensitizer (¼ cases). Long-term treatment schedules revealed no resistance development, with treated cells showing morphological signs of cell stress. Next, several combination strategies were employed to optimize ADI-based treatment. Simultaneous and sequential S. pyogenes ADI-based combinations included substances acting at different molecular pathways (curcumin, resveratrol, quinacrine, and sorafenib, 2 × 72 h treatment). Adding drugs to GBM cell lines (n = 4, including a matched pair of primary and recurrent GBM in one case) accelerated and potentiated ADI-mediated cytotoxicity. Autophagy was identified as the main cause of tumor growth inhibition. Of note, residual cells again showed classical signs of senescence in most combinations. Our results suggest an alternative treatment regimen for this fatal cancer type which circumvents many of the traditional barriers. Using the metabolic defect in GBM thus warrants further (pre-) clinical evaluation.

Arginine auxotrophy constitutes a metabolic defect that renders tumors susceptible towards arginine-depleting substances, such as bacterial arginine deiminase (ADI). In our previous studies, Arg auxotrophy and thus ADI-susceptibility was confirmed on patient-derived GBM models in vitro and in vivo. Functionally, effects were attributable to induction of autophagy, senescence and necrosis. To improve this approach, we here examined whether ADI-treatment may be combined with doxycycline (Dox) - an antibiotic with anti-cancer activities by targeting mitochondria. The effect of doxycycline was first investigated on a panel of patient-derived GBM cell lines to determine general sensitivity (N=8). Analysis revealed higher susceptibility of Arg-auxotrophic compared to Arg-prototrophic cells (N=4 cell lines each). Thereafter, doxycycline (IC(20)) was combined with ADI (35 mU/mL) in simultaneous and sequential regimens (72h each). Combined application of both agents slightly enhanced antitumoral effects of the monotherapy in selected cell lines. Decreased mitochondria content after Dox treatment was confirmed by immunofluorescence and quantitative PCR. This effect was only partially counteracted after the combination. Instead, necrosis was the dominating mode of cell death, while autophagy was found to play a minor role. No effect on radiosensitivity was seen in either treatment regimen, i.e. simultaneous or sequential. Taken together, our data support the conclusion that ADI can be combined with substances impairing mitochondria function, likely to result in an efficient oncolytic regimen. Ongoing trials focus on improvement of the treatment protocol by implementing this approach into standard clinical drug regimen and in vivo testing.

BACKGROUND Neutrophils have been proposed as important contributors to the hyperinflammatory responses that are associated with severe invasive Streptococcus pyogenes infections. In particular, streptococcal surface proteins have been implicated as potent neutrophil activators. Here we explore the impact of streptococcus-secreted factors on neutrophil activation and degranulation. METHODS Primary human neutrophils were exposed to supernatants prepared from cultures of invasive S. pyogenes strains of varying serotypes in the stationary growth phase. Neutrophil activation was assessed by measurement of secreted resistin, an azurophilic granule marker, and by determination of the secretome profile, using mass spectrometry. RESULTS Marked variation in resistin release and the neutrophil secretome profile were observed following exposure to different strains. A high resistin response was triggered exclusively by SpeB-negative strains, suggesting that at least 1 stimulatory factor is susceptible to SpeB proteolytic degradation. Further analysis, including proteomics and stimulation analyses, identified phosphoglycerate kinase as a stimulatory factor for neutrophils. CONCLUSIONS Taken together, results of this study reveal a novel secreted streptococcal factor that, in the absence of SpeB, can trigger neutrophil activation and degranulation. This finding is of interest in light of reports of hypervirulent SpeB-negative S. pyogenes variants present during invasive infections.

Genome-scale metabolic models represent the entirety of metabolic reactions of an organism based on the annotation of the respective genome. These models commonly allow all reactions to proceed concurrently, disregarding the fact that at no point all proteins will be present in a cell. The metabolic reaction space can be constrained to a more physiological state using experimentally obtained information on enzyme abundances. However, high-quality, genome-wide protein measurements have been challenging and typically transcript abundances have been used as a surrogate for protein measurements. With recent developments in mass spectrometry-based proteomics, exemplified by SWATH-MS, the acquisition of highly quantitative proteome-wide data at reasonable throughput has come within reach. Here we present methodology to integrate such proteome-wide data into genome-scale models. We applied this methodology to study cellular changes in Enterococcus faecalis during adaptation to low pH. Our results indicate reduced proton production in the central metabolism and decreased membrane permeability for protons due to different membrane composition. We conclude that proteomic data constrain genome-scale models to a physiological state and, in return, genome-scale models are useful tools to contextualize proteomic data., npj Systems Biology and Applications, 2 (1), ISSN:2056-7189

Genome-scale metabolic models comprise stoichiometric relations between metabolites, as well as associations between genes and metabolic reactions and facilitate the analysis of metabolism. We computationally reconstructed the metabolic network of the lactic acid bacterium Streptococcus pyogenes M49. Initially, we based the reconstruction on genome annotations and already existing and curated metabolic networks of Bacillus subtilis, Escherichia coli, Lactobacillus plantarum and Lactococcus lactis. This initial draft was manually curated with the final reconstruction accounting for 480 genes associated with 576 reactions and 558 metabolites. In order to constrain the model further, we performed growth experiments of wild type and arcA deletion strains of S. pyogenes M49 in a chemically defined medium and calculated nutrient uptake and production fluxes. We additionally performed amino acid auxotrophy experiments to test the consistency of the model. The established genome-scale model can be used to understand the growth requirements of the human pathogen S. pyogenes and define optimal and suboptimal conditions, but also to describe differences and similarities between S. pyogenes and related lactic acid bacteria such as L. lactis in order to find strategies to reduce the growth of the pathogen and propose drug targets.

Streptococcus pyogenes (group A streptococcus [GAS]) is a highly virulent Gram-positive bacterium. For successful infection, GAS expresses many virulence factors, which are clustered together with transcriptional regulators in distinct genomic regions. Ralp3 is a central regulator of the ERES region. In this study, we investigated the role of Ralp3 in GAS M49 pathogenesis. The inactivation of Ralp3 resulted in reduced attachment to and internalization into human keratinocytes. The Δ ralp3 mutant failed to survive in human blood and serum, and the hyaluronic acid capsule was slightly decreased. In addition, the mutant showed a lower binding capacity to human plasminogen, and the SpeB activity was significantly decreased. Complementation of the Δ ralp3 mutant restored the wild-type phenotype. The transcriptome and quantitative reverse transcription-PCR analysis of the serotype M49 GAS strain and its isogenic Δ ralp3 mutant identified 16 genes as upregulated, and 43 genes were found to be downregulated. Among the downregulated genes, there were open reading frames encoding proteins involved in metabolism (e.g., both lac operons and the fru operon), genes encoding lantibiotics (e.g., the putative salivaricin operon), and ORFs encoding virulence factors (such as the whole Mga core regulon and further genes under Mga control). In summary, the ERES region regulator Ralp3 is an important serotype-specific transcriptional regulator for virulence and metabolic control.

Lactic acid-producing bacteria survive in distinct environments, but show common metabolic characteristics. Here we studied the dynamic interactions of the central metabolism in Lactococcus lactis, extensively used as a starter culture in the dairy industry, and Streptococcus pyogenes, a human pathogen. Glucose-pulse experiments and enzymatic measurements were performed to parameterize kinetic models of glycolysis. Significant improvements were made to existing kinetic models for L. lactis, which subsequently accelerated the development of the first kinetic model of S. pyogenes glycolysis. The models revealed an important role for extracellular phosphate in the regulation of central metabolism and the efficient use of glucose. Thus, phosphate, which is rarely taken into account as an independent species in models of central metabolism, should be considered more thoroughly in the analysis of metabolic systems in the future. Insufficient phosphate supply can lead to a strong inhibition of glycolysis at high glucose concentrations in both species, but this was more severe in S. pyogenes. S. pyogenes is more efficient at converting glucose to ATP, showing a higher tendency towards heterofermentative energy metabolism than L. lactis. Our comparative systems biology approach revealed that the glycolysis of L. lactis and S. pyogenes have similar characteristics, but are adapted to their individual natural habitats with respect to phosphate regulation. Database The mathematical models described here have been submitted to the Online Cellular Systems Modelling Database and can be accessed at http://jjj.biochem.sun.ac.za/database/Levering/index.html free of charge.

Streptococcus pyogenes (group A Streptococcus [GAS]) is a major human pathogen, causing diseases ranging from mild superficial infections of the skin and pharyngeal mucosal membrane, up to severe systemic and invasive diseases and autoimmune sequelae. The capability of GAS to cause this wide variety of infections is due to the expression of a large set of virulence factors, their concerted transcriptional regulation, and bacterial adaptation mechanisms to various host niches, which we are now beginning to understand on a molecular level. The addition of -omics technologies for GAS pathogenesis investigation, on top of traditional molecular methods, led to fast progress in understanding GAS pathogenesis mechanisms. This article focuses on differential transcriptional analysis performed on the bacterial side as well as on the host cell side. The microarray studies discussed provide new insight into the following five topics: gene-expression patterns under infection-relevant conditions, gene-expression patterns in mutant strains compared with wild-type strains, emergence of exceptionally fit GAS clones, gene-expression patterns of eukaryotic target and immune cells in response to GAS infection, and mechanisms underlying shifts from a pharyngeal to invasive GAS lifestyle.

The phoPR gene locus of Clostridium acetobutylicum ATCC 824 comprises two genes, phoP and phoR . Deduced proteins are predicted to represent a response regulator and sensor kinase of a phosphate-dependent two-component regulatory system. We analyzed the expression patterns of phoPR in P i -limited chemostat cultures and in response to P i pulses. A basic transcription level under high-phosphate conditions was shown, and a significant increase in mRNA transcript levels was found when external P i concentrations dropped below 0.3 mM. In two-dimensional gel electrophoresis experiments, a 2.5-fold increase in PhoP was observed under P i -limiting growth conditions compared to growth with an excess of P i . At least three different transcription start points for phoP were determined by primer extension analyses. Proteins PhoP and an N-terminally truncated *PhoR were individually expressed heterologously in Escherichia coli and purified. Autophosphorylation of *PhoR and phosphorylation of PhoP were shown in vitro. Electromobility shift assays proved that there was a specific binding of PhoP to the promoter region of the phosphate-regulated pst operon of C. acetobutylicum .

Genome-scale metabolic models represent the entirety of metabolic reactions of an organism based on the annotation of the respective genome. These models commonly allow all reactions to proceed concurrently, disregarding the fact that at no point all proteins will be present in a cell. The metabolic reaction space can be constrained to a more physiological state using experimentally obtained information on enzyme abundances. However, high-quality, genome-wide protein measurements have been challenging and typically transcript abundances have been used as a surrogate for protein measurements. With recent developments in mass spectrometry-based proteomics, exemplified by SWATH-MS, the acquisition of highly quantitative proteome-wide data at reasonable throughput has come within reach. Here we present methodology to integrate such proteome-wide data into genome-scale models. We applied this methodology to study cellular changes in Enterococcus faecalis during adaptation to low pH. Our results indicate reduced proton production in the central metabolism and decreased membrane permeability for protons due to different membrane composition. We conclude that proteomic data constrain genome-scale models to a physiological state and, in return, genome-scale models are useful tools to contextualize proteomic data.

Streptococcus pyogenes (group A streptococci, GAS) is an exclusive human bacterial pathogen. The virulence potential of this species is tremendous. Interactions with humans range from asymptomatic carriage over mild and superficial infections of skin and mucosal membranes up to systemic purulent toxic-invasive disease manifestations. Particularly the latter are a severe threat for predisposed patients and lead to significant death tolls worldwide. This places GAS among the most important Gram-positive bacterial pathogens. Many recent reviews have highlighted the GAS repertoire of virulence factors, regulators and regulatory circuits/networks that enable GAS to colonize the host and to deal with all levels of the host immune defense. This covers in vitro and in vivo studies, including animal infection studies based on mice and more relevant, macaque monkeys. It is now appreciated that GAS, like many other bacterial species, do not necessarily exclusively live in a planktonic lifestyle. GAS is capable of microcolony and biofilm formation on host cells and tissues. We are now beginning to understand that this feature significantly contributes to GAS pathogenesis. In this review we will discuss the current knowledge on GAS biofilm formation, the biofilm-phenotype associated virulence factors, regulatory aspects of biofilm formation, the clinical relevance, and finally contemporary treatment regimens and future treatment options.

The pst operon of Clostridium acetobutylicum ATCC 824 comprises five genes, pstS , pstC , pstA , pstB , and phoU , and shows a gene architecture identical to that of Escherichia coli . Deduced proteins are predicted to represent a high-affinity p hosphate- s pecific ABC (ATP-binding cassette) t ransport system (Pst) and a protein homologous to PhoU, a negative phosphate regulon regulator. We analyzed the expression patterns of the pst operon in P i -limited chemostat cultures during acid production at pH 5.8 or solvent production at pH 4.5 and in response to P i pulses. Specific mRNA transcripts were found only when external P i concentrations had dropped below 0.2 mM. Two specific transcripts were detected, a 4.7-kb polycistronic mRNA spanning the whole operon and a quantitatively dominating 1.2-kb mRNA representing the first gene, pstS . The mRNA levels clearly differed depending on the external pH. The amounts of the full-length mRNA detected were about two times higher at pH 5.8 than at pH 4.5. The level of pstS mRNA increased by a factor of at least 8 at pH 5.8 compared to pH 4.5 results. Primer extension experiments revealed only one putative transcription start point 80 nucleotides upstream of pstS . Thus, additional regulatory sites are proposed in the promoter region, integrating two different extracellular signals, namely, depletion of inorganic phosphate and the pH of the environment. After phosphate pulses were applied to a phosphate-limited chemostat we observed faster phosphate consumption at pH 5.8 than at pH 4.5, although higher optical densities were recorded at pH 4.5.

Despite high similarity in sequence and catalytic properties, the l-lactate dehydrogenases (LDHs) in lactic acid bacteria (LAB) display differences in their regulation that may arise from their adaptation to different habitats. We combined experimental and computational approaches to investigate the effects of fructose 1,6-bisphosphate (FBP), phosphate (Pi), and ionic strength (NaCl concentration) on six LDHs from four LABs studied at pH 6 and pH 7. We found that 1) the extent of activation by FBP (Kact) differs. Lactobacillus plantarum LDH is not regulated by FBP, but the other LDHs are activated with increasing sensitivity in the following order: Enterococcus faecalis LDH2

Streptococcus pyogenes (group A streptococci [GAS]) encounter many streptococcal species of the physiological microbial biome when entering the upper respiratory tract of humans, leading to the question how GAS interact with these bacteria in order to establish themselves at this anatomic site and initiate infection. Here we show that S. oralis and S. salivarius in direct contact assays inhibit growth of GAS in a strain-specific manner and that S. salivarius , most likely via bacteriocin secretion, also exerts this effect in transwell experiments. Utilizing scanning electron microscopy documentation, we identified the tested strains as potent biofilm producers except for GAS M49. In mixed-species biofilms, S. salivarius dominated the GAS strains, while S. oralis acted as initial colonizer, building the bottom layer in mixed biofilms and thereby allowing even GAS M49 to form substantial biofilms on top. With the exception of S. oralis , artificial saliva reduced single-species biofilms and allowed GAS to dominate in mixed biofilms, although the overall two-layer structure was unchanged. When covered by S. oralis and S. salivarius biofilms, epithelial cells were protected from GAS adherence, internalization, and cytotoxic effects. Apparently, these species can have probiotic effects. The use of Affymetrix array technology to assess HEp-2 cell transcription levels revealed modest changes after exposure to S. oralis and S. salivarius biofilms which could explain some of the protective effects against GAS attack. In summary, our study revealed a protection effect of respiratory tract bacteria against an important airway pathogen and allowed a first in vitro insight into local environmental processes after GAS enter the respiratory tract.

The entry into epithelial cells and the prevention of primary immune responses are a prerequisite for a successful colonization and subsequent infection of the human host by Streptococcus pyogenes (group A streptococci, GAS). Here, we demonstrate that interaction of GAS with plasminogen promotes an integrin-mediated internalization of the bacteria into keratinocytes, which is independent from the serine protease activity of potentially generated plasmin. α(1)β(1)- and α(5)β(1)-integrins were identified as the major keratinocyte receptors involved in this process. Inhibition of integrin-linked kinase (ILK) expression by siRNA silencing or blocking of PI3K and Akt with specific inhibitors, reduced the GAS M49-plasminogen/plasmin-mediated invasion of keratinocytes. In addition, blocking of actin polymerization significantly reduced GAS internalization into keratinocytes. Altogether, these results provide a first model of plasminogen-mediated GAS invasion into keratinocytes. Furthermore, we demonstrate that plasminogen binding protects the bacteria against macrophage killing.

The myosin cross-reactive antigen (MCRA) protein family is highly conserved among different bacterial species ranging from Gram-positive to Gram-negative bacteria. Besides their ubiquitous occurrence, knowledge about the biochemical and physiological function of MCRA proteins is scarce. Here, we show that MCRA protein from Streptococcus pyogenes M49 is a FAD enzyme, which acts as hydratase on (9Z)- and (12Z)-double bonds of C-16, C-18 non-esterified fatty acids. Products are 10-hydroxy and 10,13-dihydroxy fatty acids. Kinetic analysis suggests that FAD rather stabilizes the active conformation of the enzyme and is not directly involved in catalysis. Analysis of S. pyogenes M49 grown in the presence of either oleic or linoleic acid showed that 10-hydroxy and 10,13-dihydroxy derivatives were the only products. No further metabolism of these hydroxy fatty acids was detected. Deletion of the hydratase gene caused a 2-fold decrease in minimum inhibitory concentration against oleic acid but increased survival of the mutant strain in whole blood. Adherence and internalization properties to human keratinocytes were reduced in comparison with the wild type. Based on these results, we conclude that the previously identified MCRA protein can be classified as a FAD-containing double bond hydratase, within the carbon-oxygen lyase family, that plays a role in virulence of at least S. pyogenes M49.

Background The Streptococcus pyogenes (group A streptococci, GAS) two-component signal transduction system CovRS has been described to be important for pathogenesis of this exclusively human bacterial species. If this system acts uniquely in all serotypes is currently unclear. Presence of serotype- or strain-dependent regulatory circuits and polarity is an emerging scheme in Streptococcus pyogenes pathogenesis. Thus, the contribution of the sensor kinase (CovS) of the global regulatory two-component signal transduction system CovRS on pathogenesis of several M serotypes was investigated. Results CovS mutation uniformly repressed capsule expression and hampered keratinocyte adherence in all tested serotypes. However, a serotype- and even strain-dependent contribution on survival in whole human blood and biofilm formation was noted, respectively. Conclusions These data provide new information on the action of the CovS sensor kinase and revealed that its activity on capsule expression and keratinocyte adherence is uniform across serotypes, whereas the influence on biofilm formation and blood survival is serotype or even strain dependent. This adds the CovRS system to a growing list of serotype-specific acting regulatory loci in S. pyogenes.

The Streptococcus pyogenes (group A streptococci, GAS) stand-alone Mga regulator has been shown to positively control surface-expressed virulence factors like the antiphagocytic M protein during exponential growth phase and thus, was implicated to contribute to the acute infection process. In the present study, we generated mga mutants as well as mga promoter - luciferase reporter fusions in weakly and strongly encapsulated serotype M2 and M49 GAS strains. Employing the luc reporter fusions, we showed that the complex growth medium THY-broth decreased mga expression and identified albumin as one component responsible for this effect. Fibrinogen and cU50980omponents of the complex DMEM cell culture medium induced the mga transcription rate. The attachment of mga mutants to immobilized human matrix proteins (collagen type I, fibronectin, keratin, laminin) and serum proteins (albumin, fibrinogen) was consistently reduced. Changing the Mn(2+) or Ca(2+) growth medium concentrations did not affect the fibronectin/collagen binding of M49 GAS wild-type and mga mutant strains. Medium supplementation with the oxidative stressor paraquat or anaerobic growth on THY-agar led to a relatively increased human matrix protein binding of the mga mutant. Opposite to their matrix protein-binding behaviour, the M2 and M49 mga mutants displayed an increased attachment and internalization rate for eukaryotic cells. The host cell viability was considerably reduced after prolonged exposure to mga mutants. By generating and testing corresponding M protein gene (emm) mutants, features of the eukaryotic cell interaction could not be associated to the Mga - M protein regulatory axis. In conclusion, the present results support the postulated central role of Mga regulation for GAS host colonization and acute infection stages.