Microbiology. Cracking Listeria's password

Whole Genome Analysis of Three Multi-Drug Resistant Listeria innocua and Genomic Insights Into Their Relatedness With Resistant Listeria monocytogenes

Listeria innocua are Gram-positive rod-shaped bacteria, which are not generally infectious as opposed to Listeria monocytogenes. However, the comparatively high genomic similarity between both along with on occasion, their coexistence in similar ecological niches may present the opportunity for resistance or virulence gene transfer. In this study, three multi-drug resistant L. innocua originally cultured from food were put forward for long-read genome sequencing. Chromosome and plasmid genomes were assembled and annotated. Analysis demonstrated that the resistant phenotypes correlated well with genotypes. Three plasmids pLI42, pLI203, and pLI47-1 were identified which harbor resistance islands. Sequence alignments suggested that plasmids pLI42 and pLI203 were highly similar to a previously sequenced L. monocytogenes plasmid pLR1. Similarly, another three types of resistance gene islands were observed on chromosome, including tet(M) gene islands (transposon Tn916 orthologs), dfrG gene islands and optrA-erm(A) gene islands. All three L. innocua isolates possessed listeria pathogenicity island-4 (LIPI-4) which is linked to cases of mengitis. Further genome environment and phylogenic analysis of regions flanking LIPI-4 of L. innocua and L. monocytogenes showed that these may have common origins and with the potential to transmit from the former. Our findings raise the possible need to include both L. monocytogenes and L. innocua in food surveillance programs so as to further understand of the origins of antimicrobial resistance and virulence markers of public health importance in L. monocytogenes.

Prevalence of Listeria species in food products in Isfahan, Iran

A total of 617 meat and meat products, diary, vegetables and ready to eat food samples were collected. Listeria spp. isolated by using USDA method of isolation and L. monocytogenes identified by biochemical and Polymerase Chain Reaction (PCR). The incidence of Listeria spp. was 4.6% in all food samples. L. monocytogenes was found in 1.2% of food samples. It was found that Listeria spp. was present in 6.7% of meat and meat product samples, 1.3% of diary samples, 1.2% of vegetable samples and 12% ready to eat samples. The results presented in this study indicate, the potential risk of eating ready to eat food or raw and undercooked foods.

Effect of fat content on infection by Listeria monocytogenes in a mouse model

An estimated 2,500 cases of listeriosis occur annually in the United States. Listeriosis is particularly severe among pregnant women and immunocompromised individuals. Little is known regarding the effect of the food matrix on the ability of L. monocytogenes to survive in the gastrointestinal tract and cause systemic infection. Mice were inoculated with various doses of L. monocytogenes in skim milk, Half & Half, or whipping cream to determine whether differences in milk fat content influence the ability of L. monocytogenes to survive passage through the gut and infect the liver or spleen. The number of fecal samples positive for L. monocytogenes increased with increasing doses of L. monocytogenes for all three vehicles. The number of L. monocytogenes cells isolated from liver or spleen of mice dosed with L. monocytogenes was not significantly different among treatment vehicles. Dose-response models revealed that as the dosage of L. monocytogenes was increased in different milk vehicles, the number of L. monocytogenes cells in liver or spleen also increased. Although fat content of food had no dose-dependent effect on L. monocytogenes infection in the murine gastrointestinal tract, we cannot discount the possibility that it may be a factor in L. monocytogenes infections of humans because of differences in the physiology of gastrointestinal tracts of mice and humans.

Influence of the critically ill state on host-pathogen interactions within the intestine: gut-derived sepsis redefined

Severe and prolonged states of catabolic stress have been shown to have profound effects on the intestinal tract microflora and intestinal function. Gut-derived sepsis is a term used to describe a state of systemic inflammation with organ dysfunction after severe catabolic stress hypothesized to be initiated and perpetuated by the intestinal tract microflora. Popular notions of the mechanism of this process have suggested that stress promotes the translocation of intestinal bacteria or their toxins into the systemic compartment resulting in the release of proinflammatory cytokines which participate in the systemic inflammatory response syndrome. This review is an attempt to redefine the mechanism of gut-derived sepsis by focusing on molecular events that result from host-pathogen interactions within the intestinal tract itself. This evidence-based review posits that gut-derived bacteremia, even with potent nosocomial pathogens, is an event of low proinflammatory potential and, itself, is an insufficient stimulus for the systemic inflammatory response and organ failure state typically seen after severe and prolonged catabolic stress. Mechanisms of this apparent paradox are discussed.