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

Abstract

Dairy farms are a reservoir for Listeria monocytogenes, and the reduction of this pathogen at the farm level is important for reducing human exposure. The objectives of this research were to study the diversity of L. monocytogenes strains on a single dairy farm, assess strain dynamics within the farm, identify potential sources of L. monocytogenes in bulk tank milk and milk filters, and assess the adherence abilities of representative strains. A total of 248 L. monocytogenes isolates were analyzed by pulsed-field gel electrophoresis (PFGE). Combined AscI and ApaI restriction analysis yielded 40 PFGE types (strains). The most predominant strains were T (28.6%), D (22.6%), and F (14.9%). A high level of heterogeneity of strains among isolates from fecal (Simpson's index of diversity [SID] ‫؍‬ 0.96) and environmental (SID ‫؍‬ 0.96) samples was observed. A higher homogeneity of strains was observed among isolates from milk filters (SID ‫؍‬ 0.71) and bulk tank milk (SID ‫؍‬ 0.65). Six of 17 L. monocytogenes isolates (35.3%) were classified in an in vitro assay as having a "low adherence ability," 9 (52.9%) were classified as having a "medium adherence ability," and 2 (11.8%) were classified as having a "high adherence ability." The L. monocytogenes strains that were predominant and persistent showed significantly better adherence than did strains that were only sporadic, predominant, or persistent (P ‫؍‬ 0.0006). Our results suggest that the milking system was exposed to several L. monocytogenes strains from different sources. Only 3 strains, however, were successful in persisting within the milking system, suggesting that some strains are more suitable to that particular ecological environment than others.

Quantitative Risk Assessment of Listeriosis Due to Consumption of Raw Milk†

“…For this scenario, a 25.4% prevalence of L. monocytogenes in milk was assumed, based on the laboratory results of bulk tank milk samples collected between February 2004 and March 2008 from a New York State dairy farm (32).…”

Diversity of Listeria Species in Urban and Natural Environments

“…We propose that the ability of members of the genus Listeria to establish persistent populations in different environments is critical for its widespread and ubiquitous presence. Persistence of Listeria in urban and natural environments also has important implications for studies that use reisolation of a specific Listeria subtype in a processing plant or retail environment as evidence for Listeria persistence in that location (34,37,56,57). Our data specifically indicate that reisolation of a specific Listeria subtype in a food-related environment that it is not well isolated from its surroundings (e.g., retail environments which cannot control outside traffic and install footbaths) may also, in some cases, present reintroduction of a subtype that persists in the surrounding environment.…”

Review. Dairy farm management and production practices associated with the presence of Listeria monocytogenes in raw milk and beef

“…In a different report, Review. Listeria monocytogenes from dairy farm to raw food Latorre et al (2011) presented evidence that a source of L. monocytogenes contamination was milking equipment, since 67.6% of in-line milk filter samples and 19.7% of bulk tank milk samples were positive for L. monocytogenes. Predominant and persistent strains of Listeria might be more adapted to the specific ecological environment of the milking system than strains that appear only sporadically (Vazquez-Villanueva et al, 2010;Latorre et al, 2011).…”

“…Borucki et al (2004) found that 23% of human strains isolated sporadically were identical to one or more farm isolates. Dairy farms thus appear to be a significant source of human strains of L. monocytogenes (Nightingale et al, 2004), although the degree of diversity of L. monocytogenes can be very different among different farms (Esteban et al, 2009;Fox et al, 2011;Latorre et al, 2011). Figure 2 shows PFGE characterization of a collection of L. monocytogenes isolates originating from different farms located in the Cantabria region of Northern Spain.…”

“…Some specific subtypes of L. monocytogenes can also persist for extended periods in many different food processing environments , including dairy food processing plants (Vazquez-Villanueva et al, 2010;Latorre et al, 2011). In the dairy plant, Listeria can persist in a variety of sites, although it is most frequently found in moist environments or areas with condensed or standing water or milk, including drains, floors, coolers, conveyors and case washing areas (Arimi et al, 1997;Ho et al, 2007b;Fox et al, 2009).…”