Genetic Diversity of Listeria monocytogenes Strains from a High-Prevalence Dairy Farm

Abstract

Listeria monocytogenes is a significant food-borne human and veterinary pathogen. Contaminated silage commonly leads to disease in livestock, but the pervasive nature of the bacterium can make it difficult to identify the source of infection. An investigation of bovine listeriosis that occurred on a Pacific Northwest dairy farm ("farm A") revealed that the clinical strain was closely related to fecal strains from asymptomatic cows, and that farm environment was heavily contaminated with a diversity of L. monocytogenes strains. In addition, the farm A clinical strain was closely related to clinical and environmental strains obtained 1 year prior from a second Northwest dairy farm ("farm B"). To investigate the source(s) of contamination on farm A, environmental samples were collected from farm A at two time points. Pulsed-field gel electrophoresis characterization of 538 isolates obtained from that farm identified 57 different AscI pulsovars. Fecal isolates obtained from individual cows were the most genetically diverse, with up to 94% of fecal samples containing more than one pulsovar. The maximum numbers of pulsovars and serotypes isolated from a fecal sample of one cow were 6 and 4, respectively. Serotype 1/2a was isolated most frequently at both time points. Microarray genotyping of bovine listeriosis, fecal, and silage strains from both farms identified four probes that differentiated listeriosis strains from environmental strains; however, no probe was common to both bovine listeriosis strains.

Increased In Vitro Adherence and On-Farm Persistence of Predominant and Persistent Listeria monocytogenes Strains in the Milking System

“…In contrast, a high level of heterogeneity of strains was observed among fecal and environmental L. monocytogenes isolates (SID ϭ 0.96 for each), in agreement with previous findings for fecal L. monocytogenes isolates (4,13).…”

Molecular Ecology of Listeria monocytogenes : Evidence for a Reservoir in Milking Equipment on a Dairy Farm

“…When 15 L. monocytogenes isolates obtained from fecal samples were characterized by PFGE, 12 PFGE types were observed, demonstrating a high level of heterogeneity among fecal isolates. If the presence of L. monocytogenes in bulk tank milk was due to fecal contamination, we would have expected to find heterogeneity among L. monocytogenes isolates (3,18) in the bulk tank milk as well. However, only three L. monocytogenes PFGE types, each persisting over time, were observed in milk.…”

“…Listeria is ubiquitous on dairy farms (26), and it has been isolated from cows' feces, feed (3,26), and milk (21,35). In ruminants, L. monocytogenes infections may be asymptomatic or clinical.…”

Permanent colonization of creek sediments, creek water and limnic water plants by fourListeriaspecies in low population densities

“…L. monocytogenes is carried asymptomatically in silage-fed livestock and is dropped in feces [16]. Shedding of the pathogen by a variety of domestic animals like sheep and cattle has been reported [16][17][18][19][20]. A possible route of infection into the human food chain, for instance, is through the ingestion of uncooked food plants grown on soils irrigated with contaminated water or via the consumption of vegetables cultivated on manure treated fields [21][22][23][24].…”

“…Also, ready-to-eat food or dairy products that have not been pasteurized, such as raw milk cheese or smoked salmon pose significant risks to consumers. Due to its importance as a food-borne pathogen, numerous studies on this genus deal with the occurrence and tracing of L. monocytogenes in food processing plants and in farm environments [17,[25][26][27][28][29][30].…”