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: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:Time course study of the mouse infection by comparing the genomic transcriptional patterns of Listeria monocytogenes EGDe grown under laboratory conditions (exponential growth phase) with that of in vivo-grown bacteria (in mouse spleens) over three days of infection.
Project description:Time course study of the mouse infection by comparing the genomic transcriptional patterns of Listeria monocytogenes EGDe grown under laboratory conditions (exponential growth phase) with that of in vivo-grown bacteria (in mouse spleens) over three days of infection. Time course study of the mouse infection by comparing the genomic transcriptional patterns of Listeria monocytogenes EGDe grown under laboratory conditions (exponential growth phase) with that of in vivo-grown bacteria (in mouse spleens) over three days of infection.
Project description:The SOS response is a conserved pathway that is activated under certain stress conditions and is regulated by the repressor LexA and the activator RecA. The food-borne pathogen Listeria monocytogenes contains RecA and LexA homologs, but their roles in Listeria have not been established. In this study, we identified the SOS regulon in L. monocytogenes by comparing the transcription profiles of the wild-type strain and the ΔrecA mutant strain after exposure to the DNA damaging agent mitomycinC (MMC). The SOS response is an inducible pathway involved in DNA repair, restart of stalled replication forks, and in induction of genetic variation in stressed and stationary phase cells. It is regulated by LexA and RecA. LexA is an autoregulatory repressor which binds to a consensus sequence in the promoter region of the SOS response genes, thereby repressing transcription. A consensus LexA binding motif for L. monocytogenes has not been identified thus far. Generally, the SOS response is induced under circumstances in which single stranded DNA accumulates in the cell. This results in activation of RecA, which in turn stimulates cleavage of LexA, and ultimately in the induction of the SOS response. Keywords: stress response, loop design, SOS response, mitomycin c, listeria monocytogenes, RecA, LexA
Project description:Listeria monocytogenes is a food-borne pathogen and the causative agent of listeriosis, an infection which typically arises through the consumption of contaminated foodstuffs. L. monocytogenes is a psychotrophic and facultatively anaerobic; properties which permit growth under refrigeration conditions and within modified atmosphere packaging. Through transcriptional changes L. monocytogenes is able to mount adaptive responses against stressors. Such responses typically cross protect against subsequent stresses.