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Aspergillus flavus (A. flavus) and its metabolites, aflatoxins, are widespread in crops and foods, threatening public health. Using chemical fungicides to control A. flavus can pose safety hazards and cause environmental pollution. Therefore, there is an urgent need for safe and effective antifungal agents to control A. flavus. In this study, we isolated Aspergillus luchuensis YZ-1 cell-free supernatant (CFS), volatiles, and mycelial extracts to investigate their inhibitory effects on A. flavus. Results indicate that the CFS exhibited greater efficacy in impeding the growth and synthesis of aflatoxin B1 (AFB1) in A. flavus. Transcriptomic analysis revealed a significant downregulation of lipid metabolism, biosynthesis of other secondary metabolites, and glycan metabolism in A. flavus treated with CFS. Approximately 94% of the genes in the aflatoxin synthesis pathway were significantly downregulated. Furthermore, the CFS treatment significantly increased reactive oxygen species (ROS) production in A. flavus , affected its energy metabolism, and upregulated methane metabolism and the pentose phosphate pathway. We then investigated the inhibitory mechanism of YZ-1 against A. flavus by biochemical analysis. It was further confirmed that CFS had destructive effects in the cell wall and cell membrane of A. flavus , as indicated by leakage of nucleic acids, proteins, alkaline phosphatase (AKP), as well as decreased chitin and ergosterol content. In summary, this study provides novel insights into the mechanisms of CFS against A. flavus , suggesting its potential as a biocontrol agent in food and agriculture. [Display omitted] • YZ-1 had a strong inhibitory effect on the growth and AFB1 production of A. flavus. • Transcriptomic changes in A. flavus exposed to the CFS were analyzed. • CFS induced severe oxidative stress. • CFS can act on fungal cell wall, membrane and affect cellular metabolism. [ABSTRACT FROM AUTHOR]

• The metro passengers' rescheduling strategies under COVID-19 are identified. • The scenarios with different strategies are simulated and analyzed. • The strategies can reduce the maximum passengers' density and average travel time. • The optimal strategy combination and the specific parameters are obtained. The spread of COVID-19 has a great impact on public transport which is closely related to social life. As an essential carrier of the cities, metro has become an important object of concern during the epidemic. Due to the high infection risk of COVID-19 in public space, it is necessary to quantitatively evaluate and perform corresponding epidemic control measures on reducing public health risks in metro station. In this paper, three strategies of passenger rescheduling, i.e. controlling the flows of inbound and outbound passengers in the station, setting route guidance in the crucial areas and shortening the interval time of train, are simulated and analyzed based on Anylogic. The performances of different strategies are characterized and evaluated by the important parameters, which include local passengers' density, inbound and outbound time. Finally, the optimization experiments based on an objective function are carried out to obtain the best strategy combination considering passengers' health safety and travel efficiency. The crucial areas with high density are obtained from the simulation results of the initial model. The three independent strategies are helpful in reducing the maximum passengers' density and average travel time. The optimization results of strategy combination and the specific parameters of each strategy are obtained by the final simulation experiment. The research findings are important reference to enhance the present health risk management level and provide specific measures of passenger organization in metro station under COVID-19. [ABSTRACT FROM AUTHOR]

Foodborne pathogens detection is important to ensure food safety and human health. In this study, we designed a comet structure to rapidly and sensitively detect foodborne Listeria monocytogenes. This method combined isothermal sequence exchange amplification (SEA) and surface-enhanced Raman spectroscopy. Listeria monocytogenes DNA could be rapidly amplified at a constant temperature via SEA with a pair of modified primers, which rendered the precise thermal control instrumentation unnecessary. Efficient SEA amplification generated a large number of DNA duplexes that could be easily captured by streptavidin-modified magnetic bead and AuMB@Ag-isothiocyanate fluorescein antibody (anti-FITC). AuMB@Ag-anti-FITC was used as a signal probe, which generated a significant excitation signal at 1,616 cm−1 for quantitative detection and analysis. The results displayed sensitive detection of L. monocytogenes in cheese from 2.0 × 101 cfu/mL to 2.0 × 106 cfu/mL within 1.0 h with a detection limit of 7.8 cfu/mL. Furthermore, this comet structure displayed the desirable specificity as its specific primers and amplified DNA ends were attached to streptavidin-modified magnetic beads and AuMB@Ag-anti-FITC, respectively. We expected that the method devised would provide a promising new approach to screening for L. monocytogenes and guarantee the microbiological safety of dairy products. [ABSTRACT FROM AUTHOR]

Bile salts is one of essential components of bile secreted into the intestine to confer antibacterial protection. Cronobacter species are associated with necrotizing enterocolitis in newborns and show a strong tolerance to bile salts. However, little attempt has been made to focus on the molecular basis of the tolerance to bile salts. In this study, we investigated the roles of tolC on growth, cell morphology, motility, and biofilm formation ability in Cronobacter malonaticus under bile salt stress. The results indicated that the absence of tolC significantly affected the colony morphology and outer membrane structure in a normal situation, compared with those of the wild type strain. The deletion of tolC caused the decline in resistance to bile salt stress, inhibition of growth, and observable reduction in relative growth rate and motility. Moreover, the bacterial stress response promoted the biofilm formation ability of the mutant strain. The expression of the AcrAB-TolC system (acrA, acrB , and tolC) was effectively upregulated compared with the control sample when exposed to different bile salt concentrations. The findings provide valuable information for deeply understanding molecular mechanisms about the roles of tolC under bile salt stress and the prevention and control of C. malonaticus. [ABSTRACT FROM AUTHOR]

Abstract Cronobacter species are associated with rare but severe infections in newborns, and their tolerance to environmental stress such as acid stress has been described. However, the factors involved in low acid tolerance in Cronobacter are poorly understood. Here, a transposon mutagenesis approach was used to explore the factors involved in acid tolerance in C. malonaticus. Eight mutants from mutant library (n = 215) were successfully screened through a comparison of growth with wild type (WT) strain under acid stress (pH 4.0). Eight mutating sites including glucosyltransferase MdoH, extracellular serine protease, sulfate transporter, phosphate transporter permease subunit PstC, lysine transporter, nitrogen regulation protein NR (II), D-alanine-D-alanine ligase, glucan biosynthesis protein G were successfully identified by arbitrary polymerase chain reaction and sequencing. The biomass of biofilm of eight mutants were significantly reduced using crystal violet staining (CVS) compared with that of WT. furthermore, the more compact biofilms of WT was observed than those of eight mutants through scanning electron microscopy (SEM), and confocal laser scanning microscopy (CLSM). Disassembly of biofilms appeared among mutants and WT strain from 48 h to 72 h through the increasing of dead cells and reduction of viable cells and exopolysaccharide. The study reveals the molecular basis involved in acid tolerance of C. malonaticus and a possible relationship between biofilm formation and acid tolerance, which provides valuable information for survival of C. malonaticus under acid stress. Highlights • Using random mutagenesis, Cronobacter malonaticus mutant library was developed; • Factors involved in acid stress in C. malonaticus were successfully identified; • Biofilm formation in mutants were significantly reduced compared with those of parent strain; • Biofilm formation might contribute to low acid tolerance in C. malonaticus. Graphical abstract Unlabelled Image [ABSTRACT FROM AUTHOR]

Cronobacter malonaticus is one of the opportunistic food-borne pathogens in powdered infant formula and has unusual abilities to survive under environmental stresses such as osmotic conditions. However, the genes involved in osmotic stress have received little attention in C. malonaticus. Here, genes involved in osmotic stress were determined in C. malonaticus using a transposon mutagenesis approach. According to the growth of mutants (n = 215) under 5.0% NaCl concentration, the survival of 5 mutants under osmotic stress was significantly decreased compared with that of the wild type strain. Five mutating sites, including potassium efflux protein KefA, inner membrane protein YqjF, peptidylprolyl isomerase, Cys-tRNA(Pro)/CystRNA( Cys) deacylase, and oligogalacturonate lyase were successfully identified. In addition, the biofilm formation of 5 mutants was determined using crystal violet staining, scanning electron microscopy, and confocal laser scanning microscopy, and the biofilms of 5 mutants significantly decreased within 72 h compared with that of wild type strain. This is the first report to determine the genes involved in osmotic tolerance in C. malonaticus. The findings provided valuable information for deep understanding of the mechanism of survival of C. malonaticus under osmotic stress, and a possible relationship between biofilm formation and tolerance to osmotic stress was also demonstrated in C. malonaticus. [ABSTRACT FROM AUTHOR]

Cronobacter sakazakii is associated with severe infections including sepsis, neonatal meningitis, and necrotizing enterocolitis. Antibiotic resistance in Cronobacter species has been documented in recent years, but the genes involved in resistance in Cronobacter strains are poorly understood. In this study, we determined the role of outer membrane protein W (OmpW) on survival rates, morphologic changes, and biofilm formation between wild type (WT) and an OmpW mutant strain (ΔOmpW) under neomycin sulfate stress. Results indicated that the survival rates of ΔOmpW were significantly reduced after half minimum inhibitory concentration (1/2 MIC) treatment compared with the WT strain. Filamentation of C. sakazakii cells was observed after 1/2 MIC treatment in WT and ΔOmpW, and morphologic injury, including cell disruption and leakage of cells, was more predominant in ΔOmpW. Under 1/2 MIC stress, the biofilms of WT and ΔOmpW were significantly decreased, but decreasing rates of biofilm formation in mutant strain were more predominant compared with WT strain. This is the first report to determine the role of OmpW on survival, morphological changes, and biofilm formation in C. sakazakii under neomycin sulfate stress. The findings indicated that OmpW contributed to survival and reduction of morphological injury under neomycin sulfate stress. In addition, enhancing biofilm formation in ΔOmpW may be an alternative advantage for adaptation to neomycin sulfate stress. [ABSTRACT FROM AUTHOR]

In recent years, food poisoning events caused by Vibrio parahaemolyticus have shown an upward trend. Therefore, there is a growing need for a rapid, sensitive and simple detection method for V. parahaemolyticus. The aim of this study was to develop a novel aptamer-based paper sensor for the rapid, sensitive, portable and specific detection of V. parahaemolyticus in seafood through the fluorescence resonance energy transfer (FRET) principle. The capture probes for this strategy were made by chemically coupling carbon dots (CDs) to amino-modified single-stranded DNA. Switches were double-stranded DNA formed by hybridization of anti- V. parahaemolyticus aptamers (aptamer) and gold nanoparticles (AuNPs)-probes. Once V. parahaemolyticus was introduced, the aptamer in the double-stranded DNA bound specifically to the target bacteria and the sensor was 'On', releasing the AuNPs-probes to bind to the capture probes. The fluorescence color of the CDs changed significantly from bright blue to colorless because of the FRET between CDs and AuNPs. As expected, when filter paper was used as the assay liquid carrier, an ingenious FRET-based paper sensor was presented for accurate field reporting of V. parahaemolyticus , with a linear range of 101-106 cfu/mL. This strategy has a detection limit of 8.9 cfu/mL for V. parahaemolyticus in culture and 6.7 × 101 cfu/mL in artificially contaminated cod samples. The results indicate that this study has good potential as a new portable sensor for the detection of V. parahaemolyticus in complex food matrices. • Novel FRET-based paper strip was developed to detect Vibrio parahaemolyticus. • FRET-based paper strip with smartphone for field detection of Vibrio parahaemolyticus. • Fast response time, high sensitivity and specificity of this sensor for Vibrio parahaemolyticus. • The sensor has good practicability in fish samples. [ABSTRACT FROM AUTHOR]

Cronobacter malonaticus is one of the important foodborne pathogens causing infections mainly in adults. Biofilm formation, adhesion, and motility in Cronobacter have been documented, but the implying molecular mechanism has received little attention. Here, a comparison in biofilm formation, adhesion ability, and cell motility among wild type (WT), △ luxS , and △ fliC strains were analyzed using scanning electron microscope (SEM) and confocal laser scanning microscopy (CLSM). The thickest biofilm was formed by WT, followed by △ luxS and △ fliC. Furthermore, the deletion of fliC caused the loss of cell motility and the failure to flagella biosynthesis and mature biofilm formation. Besides, the adhesion abilities of △ luxS and △ fliC to biotic cells (LoVo and IEC-6) and abiotic surface (glass) were significantly decreased compared to WT, revealing that fliC might have an important role in the organism's invasion properties. We further demonstrated that the expression of negative regulator (flgM) of flagellin in △ luxS was higher than that in WT, which indicated that luxS indirectly contributed to fliC expression. Our findings provided a novel perspective for precaution and control of C. malonaticus through intercepting fliC -mediated adhesion to biotic cells and abiotic surface. • C. malonaticus △fliC failed to flagella biosynthesis and mature biofilms formation. • Deletion of fliC resulted in the loss of swimming motility and the adhesion to abiotic surfaces and biotic cells;. • C. malonaticus luxS contributed to expression of fliC through negatively regulating flgM. [ABSTRACT FROM AUTHOR]