Project description:Listeria monocytogenes strains classify into at least three distinct phylogenetic lineages. Correlations exist between lineage classification and source of bacterial isolation, e.g., human clinical and food isolates usually classify into either lineage I or II, however, human clinical isolates are over-represented in lineage I while food isolates are over-represented in lineage II. σB, a transcriptional regulator previously demonstrated to contribute to environmental stress response and virulence in L. monocytogenes lineage II strains, was hypothesized to provide differential capabilities for L. monocytogenes survival in various niches (e.g., food vs. human clinical). To determine if σB contributions to stress response and virulence differ across diverse L. monocytogenes strains, ΔsigB mutations were created in strains from lineages I, II, IIIA, and IIIB. Paired parent and ΔsigB mutant strains were tested for acid and oxidative stress survival, Caco-2 cell invasion efficiency, and virulence using the guinea pig listeriosis infection model. Parent and ΔsigB mutant strain transcriptomes were compared using whole-genome expression microarrays. σB contributed to virulence in each strain. However, while σB contributed significantly to acid and oxidative stress survival and Caco-2 cell invasion in lineage I, II, and IIIB strains, σB contributions were not significant for these phenotypes in the lineage IIIA strain. A core set of 63 genes was positively regulated by σB in all four strains; different total numbers of genes were positively regulated by σB in each strain. Our results suggest that σB universally contributes to L. monocytogenes virulence, but specific σB-regulated stress response phenotypes vary among strains.
Project description:Listeria monocytogenes strains classify into at least three distinct phylogenetic lineages. Correlations exist between lineage classification and source of bacterial isolation, e.g., human clinical and food isolates usually classify into either lineage I or II, however, human clinical isolates are over-represented in lineage I while food isolates are over-represented in lineage II. σB, a transcriptional regulator previously demonstrated to contribute to environmental stress response and virulence in L. monocytogenes lineage II strains, was hypothesized to provide differential capabilities for L. monocytogenes survival in various niches (e.g., food vs. human clinical). To determine if σB contributions to stress response and virulence differ across diverse L. monocytogenes strains, ΔsigB mutations were created in strains from lineages I, II, IIIA, and IIIB. Paired parent and ΔsigB mutant strains were tested for acid and oxidative stress survival, Caco-2 cell invasion efficiency, and virulence using the guinea pig listeriosis infection model. Parent and ΔsigB mutant strain transcriptomes were compared using whole-genome expression microarrays. σB contributed to virulence in each strain. However, while σB contributed significantly to acid and oxidative stress survival and Caco-2 cell invasion in lineage I, II, and IIIB strains, σB contributions were not significant for these phenotypes in the lineage IIIA strain. A core set of 63 genes was positively regulated by σB in all four strains; different total numbers of genes were positively regulated by σB in each strain. Our results suggest that σB universally contributes to L. monocytogenes virulence, but specific σB-regulated stress response phenotypes vary among strains.
Project description:Persistence of Listeria monocytogenes in retail deli environments is a serious food safety issue, potentially leading to cross-contamination of ready-to-eat foods such as deli meats, salads, and cheeses. We previously discovered strong evidence of L. monocytogenes persistence in delis across multiple states. We hypothesized that this was correlated with isolates’ innate characteristics, such as biofilm-forming capacity or gene differences.We further chose four isolates for RNA-sequencing analysis and compared their global biofilm transcriptome to their global planktonic transcriptome. Analysis of biofilm vs planktonic gene expression did not show the expected differences in gene expression patterns. Overall, L. monocytogenes persistence in the deli environment is likely a matter of poor sanitation and/or facility design, rather than isolates’ biofilm-forming capacity, sanitizer tolerance, or genomic content
Project description:This study explored the mode of action of glabridin, a prenylated isoflavan with antimicrobial activity, against L. monocytogenes, an important food-borne pathogen.
Project description:Peracetic acid (PAA), a strong oxidizing agent, has been widely used as a disinfectant in food processing settings as it does not produce harmful chlorinated by-products. In the present study, the transcriptional response of Listeria monocytogenes to 2.5 ppm of PAA was assessed using RNA-sequencing (RNA-seq). Our analysis revealed 12 differentially expressed genes, of which 9 were up-regulated (ohrR, ohrA, rpsN, lmo0637, lmo1973, fur, lmo2492, zurM, and lmo1007), and 3 were down-regulated (argG, lmo0604, lmo2156) in PAA treated samples compared to the control samples. A non-coding small RNA (rli32) was also found to be down-regulated. In detail, the organic peroxide toxicity protection (OhrA-OhrR) system, the metal homeostasis genes fur and zurM, the SbrE-regulated lmo0636-lmo0637 operon and a carbohydrate phosphotransferase system (PTS) operon component were induced under exposure of L. monocytogenes to PAA. Hence, this study identified key elements involved in the primary response of L. monocytogenes to oxidative stress caused by PAA. The investigation of the molecular mechanism of PAA response in L. monocytogenes is of utmost importance for the food industry, as this response can be induced in food-processing environments, as a result of inadequate rinsing during the disinfection process, that lead to PAA residues at low concentrations.