Listeria monocytogenes is a facultative intracellular pathogen thought to be widely distributed in the environment. We investigated the prevalence and characteristics of L. monocytogenes isolates from surface waters derived from catchments within the South Nation River watershed (Ontario, Canada). This watershed is dominated by urban and rural development, livestock and crop production, and wildlife habitats. From June to November 2005, a total of 314 surface water samples were collected biweekly from 22 discrete sampling sites characterized by various upstream land uses. Presumptive Listeria spp. were isolated using a selective enrichment and isolation procedure, and 75 L. monocytogenes isolates were identified based on colony morphology, hemolytic activity, and amplification of three pathogenicity genes: iap, inlA, and hlyA. Thirty-two of 314 (10%) surface water samples were positive for the presence of L. monocytogenes, but detection ranged between 0 and 27% depending on the sampling date. Isolates belonging to serovar group 1/2a, 3a (50%) and group 4b, 4d, 4e (32%) were dominant. L. monocytogenes populations were resolved into 13 EcoRI ribotypes and 21 ApaI and 21 AscI pulsotypes. These had Simpson indexes of discrimination of up to 0.885. Lineage I-related isolates were dominant (61%) during the summer, whereas lineage II isolates were dominant (77%) in the fall. Isolates were, on average, resistant to 6.1 ؎ 2.1 antibiotics out of 17 tested. Half of the L. monocytogenes isolates exhibited potential virulence linked to the production of a functional internalin A, and some isolates were found to be moderately to highly virulent by in vitro Caco-2 plaque formation assay (up to 28% of entry). There was a statistically significant link between the occurrence of L. monocytogenes and proximity to an upstream dairy farm and degree of cropped land. Our data indicate that L. monocytogenes is widespread in the studied catchments, where it could represent a public health issue related to agricultural land use.Listeria monocytogenes is a gram-positive facultative intracellular pathogen responsible for severe food-borne infections in humans and causes 20 to 50% mortality in susceptible populations, such as newborn children, the elderly, and immunocompromised persons (22,56). This bacterium is thought to be a saprophytic organism living naturally in the plant-soil environment, where it can survive for up to several months, being able to multiply in decaying vegetation but unlikely to multiply in soil (16). In the natural environment, biotic and abiotic factors shown to reduce L. monocytogenes survival are predation, high temperature, UV exposure, and low moisture (12,16,20). Soil texture also influences L. monocytogenes survival, but the availability of inorganic nutrients (nitrogen and phosphorus) does not influence survival (12).A possible agricultural route of human exposure is through the ingestion of uncooked food crops grown in soil irrigated with contaminated water and/or fertilized with Listeria-contaminated manur...

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Listeria monocytogenes is a facultative intracellular pathogen that can be carried asymptomatically in various animals and can be shed in feces. We investigated the prevalence and characteristics of L. monocytogenes isolated from livestock, wildlife, and human potential sources of contamination in 2 areas in Ontario, Canada. From February 2003 to November 2005, a total of 268 fecal samples were collected from different animals. Listeria monocytogenes was isolated using selective enrichment, isolation, and confirmation procedures, and 15 samples (6%) yielded to the isolation of 84 confirmed strains. Listeria monocytogenes was isolated from livestock (beef and dairy), wildlife (deer, moose, otter, and raccoon), and human (biosolids and septic) fecal sources. Thirty-two isolates were from serovar 1/2a, 34 from serovar 1/2b, 1 from serovar 3a, and 17 from serovar 4b. Listeria monocytogenes populations were resolved into 13 EcoRI ribotypes, and 18 ApaI and 18 AscI pulsotypes, with Simpson indexes of discrimination of 0.878 and 0.907, respectively. A majority (59%) of L. monocytogenes isolates exhibited potential virulence linked to the production of a functional internalin A, which was supported by higher entry into Caco-2 cells (9.3%) than isolates producing truncated and secreted internalin A (1.3% of entry). Listeria monocytogenes fecal isolates were on average resistant to 6.4 +/- 2.5 antibiotics out of 17 tested, and potentially virulent isolates exhibited an enhanced resistance to kanamycin, gentamicin, streptomycin, and rifampicin. Livestock, wildlife, and human L. monocytogenes fecal communities exhibited overlapping but distinct populations, and some genotypes and phenotypes were similar to those previously described for surface water isolates in the same area.