Factors affecting survival of Listeria monocytogenes and Listeria innocua in soil samples

While rain and irrigation events have been associated with an increased prevalence of foodborne pathogens in produce production environments, quantitative data are needed to determine the effects of various spatial and temporal factors on the risk of produce contamination following these events. This study was performed to quantify these effects and to determine the impact of rain and irrigation events on the detection frequency and diversity of Listeria species (including L. monocytogenes) and L. monocytogenes in produce fields. Two spinach fields, with high and low predicted risks of L. monocytogenes isolation, were sampled 24, 48, 72, and 144 to 192 h following irrigation and rain events. Predicted risk was a function of the field's proximity to water and roads. Factors were evaluated for their association with Listeria species and L. monocytogenes isolation by using generalized linear mixed models (GLMMs). In total, 1,492 (1,092 soil, 334 leaf, 14 fecal, and 52 water) samples were collected. According to the GLMM, the likelihood of Listeria species and L. monocytogenes isolation from soil samples was highest during the 24 h immediately following an event (odds ratios [ORs] of 7.7 and 25, respectively). Additionally, Listeria species and L. monocytogenes isolates associated with irrigation events showed significantly lower sigB allele type diversity than did isolates associated with precipitation events (P ‫؍‬ <0.001), suggesting that irrigation water may be a point source of L. monocytogenes contamination. Small changes in management practices (e.g., not irrigating fields before harvest) may therefore reduce the risk of L. monocytogenes contamination of fresh produce. Foodborne outbreaks have been increasingly linked to fresh produce in the United States (1-6). In fact, the proportion of foodborne outbreaks that were attributed to produce between 1998 and 2008, 46%, was over twice that attributed to meat, 22% (6). Similarly, between 2002 and 2011, produce-associated outbreaks caused, on average, more illnesses per outbreak than any other food (1). As a result, the safety of fresh produce has come into question, negatively affecting produce growers, the food industry, and local economies (7,8). For example, as a consequence of a 2011 listeriosis outbreak linked to fresh cantaloupes in the United States (9), cantaloupe consumption dropped nationwide by 53% (10). The instability of the cantaloupe market following the 2011 outbreak is indicative of a larger trend of wide-scale consumer avoidance of products associated with outbreaks, even when the outbreak is associated with point source events (7,8). Thus, prevention of produce-associated outbreaks is a key concern of the produce industry. Although most listeriosis outbreaks associated with fresh produce are traced back to processing environments, the prevention of produce contamination in production environments is crucial. In fact, previous studies have shown that low-level sporadic contamination of produce in production environments can result in pathogen pr...

Section: Discussionmentioning

confidence: 99%

Spatial and Temporal Factors Associated with an Increased Prevalence of Listeria monocytogenes in Spinach Fields in New York State

Weller

Wiedmann

Strawn

2015

“…More generally, because the composition and structure of the microbial communities are structured by the complex characteristics of the abiotic environment (43)(44)(45), it is difficult to address the weight of a single parameter on the overall survival of L. monocytogenes in soil. Nevertheless, there is clear evidence that the biotic environment is a key player in the control of the populations of L. monocytogenes, as evidenced by comparisons of population dynamics in microcosms of sterilized and unsterilized soils (9,46,47). Moreover, in a study of experimental ecology, erosion of the soil microbial diversity resulted in the persistence of the population of L. monocytogenes in soil (48).…”

Section: Discussionmentioning

confidence: 99%

Survival of Listeria monocytogenes in Soil Requires AgrA-Mediated Regulation

Vivant

Garmyn

Gal

et al. 2015

In this study, we investigated whether the Agr-mediated response is triggered during adaptation in soil, and we compared survival patterns in a set of 10 soils. The fate of the parental strain L. monocytogenes L9 (a rifampin-resistant mutant of L. monocytogenes EGD-e) and that of a ⌬agrA deletion mutant were compared in a collection of 10 soil microcosms. The ⌬agrA mutant displayed significantly reduced survival in these biotic soil microcosms, and differential transcriptome analyses showed large alterations of the transcriptome when AgrA was not functional, while the variations in the transcriptomes between the wild type and the ⌬agrA deletion mutant were modest under abiotic conditions. Indeed, in biotic soil environments, 578 protein-coding genes and an extensive repertoire of noncoding RNAs (ncRNAs) were differentially transcribed. The transcription of genes coding for proteins involved in cell envelope and cellular processes, including the phosphotransferase system and ABC transporters, and proteins involved in resistance to antimicrobial peptides was affected. Under sterilized soil conditions, the differences were limited to 86 genes and 29 ncRNAs. These results suggest that the response regulator AgrA of the Agr communication system plays important roles during the saprophytic life of L. monocytogenes in soil. Listeria monocytogenes is the causative agent of listeriosis, a serious foodborne infection affecting essentially immunocompromised individuals, the elderly, and pregnant women (1). The pathogen is largely spread in the environment. It has been isolated from water systems (2-4), vegetation (5), soil (6-8), farms (9-12), food industries (13-15), and the feces of animals (16-18). Environmental adaptation requires that the cell have the ability to integrate environmental cues in order to adapt its physiology to the surrounding conditions through the regulation of gene expression. Genomics showed that an important part of the L. monocytogenes genome (7.3%) is dedicated to regulation and includes 209 transcriptional regulators, 15 histidine kinases, and 16 response regulators constituting two-component systems (19). Two-component systems participate in the ability of bacteria to sense and respond to fluctuating environmental conditions. AgrC/AgrA is a two-component regulatory system that is part of the Agr communication system. Initially described in Staphylococcus aureus, this communication system is organized as a four-gene operon, agrBDCA. AgrB is a membrane-bound protein that processes the propeptide AgrD into a mature autoinducing peptide (AIP). Detection of AIP by the histidine kinase AgrC induces transcriptional regulation through activation of the regulator AgrA. Detailed data concerning the role of the Agr system in the physiology of S. aureus are available (20)(21)(22). So far, its role in the adaptation of L. monocytogenes to its environment is only partially understood (23). Reports show that the Agr communication system of L. monocytogenes is involved in adhesion to abiotic surfaces (24) in ...

“…In Maryland, January 2014 (year 1) and February 2015 (year 2) were the 12th (48) and 6th (49) coldest on record, respectively. Previous research has shown that L. monocytogenes survives better at 5°C than at 15 to 20°C (50,51), and it is able to survive in soil for extended periods at low temperatures (52,53). The persistence of pathogenic Listeria spp.…”

Section: Discussionmentioning

confidence: 99%

Effects of Cover Crop Species and Season on Population Dynamics of Escherichia coli and Listeria innocua in Soil

Reed-Jones

Marine

Everts

et al. 2016

dCover crops provide several ecosystem services, but their impact on enteric bacterial survival remains unexplored. The influence of cover cropping on foodborne pathogen indicator bacteria was assessed in five cover crop/green manure systems: cereal rye, hairy vetch, crimson clover, hairy vetch-rye and crimson clover-rye mixtures, and bare ground. Cover crop plots were inoculated with Escherichia coli and Listeria innocua in the fall of 2013 and 2014 and tilled into the soil in the spring to form green manure. Soil samples were collected and the bacteria enumerated. Time was a factor for all bacterial populations studied in all fields (P < 0.001). E. coli levels declined when soil temperatures dipped to <5°C and were detected only sporadically the following spring. L. innocua diminished somewhat but persisted, independently of season. In an organic field, the cover crop was a factor for E. coli in year 1 (P ‫؍‬ 0.004) and for L. innocua in year 2 (P ‫؍‬ 0.011). In year 1, E. coli levels were highest in the rye and hairy vetch-rye plots. In year 2, L. innocua levels were higher in hairy vetch-rye (P ‫؍‬ 0.01) and hairy vetch (P ‫؍‬ 0.03) plots than in the rye plot. Bacterial populations grew (P < 0.05) or remained the same 4 weeks after green manure incorporation, although initial reductions in L. innocua numbers were observed after tilling (P < 0.05). Green manure type was a factor only for L. innocua abundance in a transitional field (P < 0.05). Overall, the impacts of cover crops/green manures on bacterial population dynamics in soil varied, being influenced by bacterial species, time from inoculation, soil temperature, rainfall, and tillage; this reveals the need for long-term studies. In agricultural environments, soil can serve as a reservoir and route of transmission for foodborne pathogens (1). Since fresh produce is often consumed raw without a "kill step" to inactivate human-pathogenic microorganisms, it is important to prevent the contamination of these foods during production (2). Growers may implement good agricultural practices (GAPs) to minimize the risk of produce contamination at the preharvest level (3), as this program focuses on on-farm risk factors, including animalbased fertilizers, irrigation water quality, farm worker training and hygiene, and wildlife exclusion. Outbreaks and contamination events, however, continue to occur, emphasizing the need to evaluate the role of other agricultural practices, which thus far have received less attention, on enteric pathogen dynamics on a farm.One such practice is cover cropping, the establishment of a crop, typically a small grain or legume, in between cultivations of a cash crop. In recent years, economic and environmental considerations have renewed interest in this old practice for improving crop productivity and soil health and maintaining the sustainability of agroecosystems (4). Cover cropping brings a variety of ecosystem services to agricultural systems, including seasonal protection of soil from erosion, weed suppression, soil improvement, a...