Abstract
The fate of two strains of Listeria monocytogenes and their ability to become viable but non-culturable (VBNC) was investigated in microcosms containing piggery effluents (two raw manures and two biologically treated manures) stored for 2 months at 8 and 20°C. Levels of L. monocytogenes were estimated using the culture method, qPCR, and propidium monoazide treatment combined with qPCR (qPCRPMA). The chemical composition and the microbial community structure of the manures were also analyzed. The strains showed similar decline rates and persisted up to 63 days. At day zero, the percentage of VBNC cells among viable cells was higher in raw manures (81.5–94.8%) than in treated manures (67.8–79.2%). The changes in their proportion over time depended on the temperature and on the type of effluent: the biggest increase was observed in treated manures at 20°C and the smallest increase in raw manures at 8°C. The chemical parameters had no influence on the behavior of the strains, but decrease of the persistence of viable cells was associated with an increase in the microbial richness of the manures. This study demonstrated that storing manure altered the culturability of L. monocytogenes, which rapidly entered the VBNC state, and underlines the importance of including VBNC cells when estimating the persistence of the pathogens in farm effluents.
Highlights
The presence of Listeria monocytogenes, a food-borne pathogen, has been demonstrated in animal feces, manure and farm wastewaters (Farzan et al, 2010; Hellstrom et al, 2010; Boscher et al, 2012; Dungan et al, 2012; Pourcher et al, 2012)
The difference in Log10 reduction for a given matrix after 63 days of incubation at between 8 and 20◦C ranged from 0.4 Log10 (Lagoon-1) to 5 Log10 (Manure-2). This is consistent with the results reported by Klein et al (2011), who compared the behavior of an inoculated strain of L. monocytogenes in microcosms containing stockpiled or composted manure
This study showed that the survival of L. monocytogenes, which was shorter at 20◦C than at 8◦C, did not depend on the serotype or on the origin of the strain
Summary
The presence of Listeria monocytogenes, a food-borne pathogen, has been demonstrated in animal feces, manure and farm wastewaters (Farzan et al, 2010; Hellstrom et al, 2010; Boscher et al, 2012; Dungan et al, 2012; Pourcher et al, 2012). Humans can be exposed to L. monocytogenes strains by direct contact through farming operations or indirectly through consumption of food contaminated by manure from infected or shedding animals (Schlech et al, 1983; Nightingale et al, 2004; Mohammed et al, 2010). It has been reported that cattle farm ecosystems maintain a high prevalence of L. monocytogenes, including subtypes linked to human listeriosis (Nightingale et al, 2004). Lyautey et al (2007) showed a link between the occurrence of L. monocytogenes in surface waters in agricultural catchments in Ontario (Canada), the extent of cropped land and proximity to an upstream dairy operation. Farm environments may act as a vehicle for the dissemination of L. monocytogenes
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