Tracking Salmonella Contamination in Various Watersheds and Phenotypic and Genotypic Diversity

111

bThe consumption of fresh tomatoes has been linked to numerous food-borne outbreaks involving various serovars of Salmonella enterica. Recent advances in our understanding of plant-microbe interactions have shown that human enteric pathogenic bacteria, including S. enterica, are adapted to survive in the plant environment. In this study, tomato plants (Solanum lycopersicum cv. Micro-Tom) grown in sandy loam soil from Virginia's eastern shore (VES) were inoculated with S. enterica serovars to evaluate plausible internalization routes and to determine if there is any niche fitness for certain serovars. Both infested soil and contaminated blossoms can lead to low internal levels of fruit contamination with Salmonella. Salmonella serovars demonstrated a great ability to survive in environments under tomato cultivation, not only in soil but also on different parts of the tomato plant. Of the five serovars investigated, Salmonella enterica serovars Newport and Javiana were dominant in sandy loam soil, while Salmonella enterica serovars Montevideo and Newport were more prevalent on leaves and blossoms. It was also observed that Salmonella enterica serovar Typhimurium had a poor rate of survival in all the plant parts examined here, suggesting that postharvest contamination routes are more likely in S. Typhimurium contamination of tomato fruit. Conversely, S. Newport was the most prevalent serovar recovered in both the tomato rhizosphere and phyllosphere. Plants that were recently transplanted (within 3 days) had an increase in observable internalized bacteria, suggesting that plants were more susceptible to internalization right after transplant. These findings suggest that the particular Salmonella serovar and the growth stage of the plant were important factors for internalization through the root system.

Section: Discussionmentioning

confidence: 98%

Colonization and Internalization of Salmonella enterica in Tomato Plants

Zheng

Allard

Reynolds

et al. 2013

111

“…Other surveys in different regions of the United States reported a lower percentage of MDR isolates from agricultural water. For example, only one MDR isolate (serotype Miami) was isolated from agricultural water in North Carolina (45), and a survey of water samples from 14 tomato farms in mid-Atlantic coast states found only three (4.8%) MDR Salmonella strains (42). However, none of our MDR patterns overlapped with the MDR patterns in those studies, except that streptomycin resistance was widely distributed among the MDR strains in most cases, possibly due to the widespread streptomycin exposure of bacteria in soil (46).…”

Section: Figmentioning

confidence: 99%

Distribution and Characterization of Salmonella enterica Isolates from Irrigation Ponds in the Southeastern United States

Luo

Ginn

et al. 2015

f Irrigation water has been implicated as a likely source of produce contamination by Salmonella enterica. Therefore, the distribution of S. enterica was surveyed monthly in irrigation ponds (n ‫؍‬ 10) located within a prime agricultural region in southern Georgia and northern Florida. All ponds and 28.2% of all samples (n ‫؍‬ 635) were positive for Salmonella, with an overall geometric mean concentration (0.26 most probable number [MPN]/liter) that was relatively low compared to prior reports for rivers in this region. Salmonella peaks were seasonal; the levels correlated with increased temperature and rainfall (P < 0.05). The numbers and occurrence were significantly higher in water (0.32 MPN/liter and 37% of samples) than in sediment (0.22 MPN/ liter and 17% of samples) but did not vary with depth. Representative isolates (n ‫؍‬ 185) from different ponds, sample types, and seasons were examined for resistance to 15 different antibiotics; most strains were resistant to streptomycin (98.9%), while 20% were multidrug resistant (MDR) for 2 to 6 antibiotics. DiversiLab repetitive extragenic palindromic-element sequence-based PCR (rep-PCR) revealed genetic diversity and showed 43 genotypes among 191 isolates, as defined by >95% similarity. The genotypes did not partition by pond, season, or sample type. Genetic similarity to known serotypes indicated Hadar, Montevideo, and Newport as the most prevalent. All ponds achieved the current safety standards for generic Escherichia coli in agricultural water, and regression modeling showed that the E. coli level was a significant predictor for the probability of Salmonella occurrence. However, persistent populations of Salmonella were widely distributed in irrigation ponds, and the associated risks for produce contamination and subsequent human exposure are unknown, supporting continued surveillance of this pathogen in agricultural settings.

“…A number of studies have shown that water can act as both a source of pathogens and a vehicle of pathogen introduction to preharvest environments and produce (20,(22)(23)(24)(25). For example, surface water has been reported to have a wide range of Salmonella (6% to 80%) and L. monocytogenes (6.4% to 62%) prevalence (24,(26)(27)(28)(29). In particular, Salmonella prevalence of 6 to 9% has been reported for water samples obtained from produce-growing regions in California and New York State (14,23).…”

mentioning

confidence: 99%

Risk Factors Associated with Salmonella and Listeria monocytogenes Contamination of Produce Fields

Strawn

Gröhn

Warchocki

et al. 2013

147

122

cIdentification of management practices associated with preharvest pathogen contamination of produce fields is crucial to the development of effective Good Agricultural Practices (GAPs). A cross-sectional study was conducted to (i) determine management practices associated with a Salmonella-or Listeria monocytogenes-positive field and (ii) quantify the frequency of these pathogens in irrigation and nonirrigation water sources. Over 5 weeks, 21 produce farms in New York State were visited. Fieldlevel management practices were recorded for 263 fields, and 600 environmental samples (soil, drag swab, and water) were collected and analyzed for Salmonella and L. monocytogenes. Management practices were evaluated for their association with the presence of a pathogen-positive field. Salmonella and L. monocytogenes were detected in 6.1% and 17.5% of fields (n ‫؍‬ 263) and 11% and 30% of water samples (n ‫؍‬ 74), respectively. The majority of pathogen-positive water samples were from nonirrigation surface water sources. Multivariate analysis showed that manure application within a year increased the odds of a Salmonellapositive field (odds ratio [OR], 16.7), while the presence of a buffer zone had a protective effect (OR, 0.1). Irrigation (within 3 days of sample collection) (OR, 6.0), reported wildlife observation (within 3 days of sample collection) (OR, 6.1), and soil cultivation (within 7 days of sample collection) (OR, 2.9) all increased the likelihood of an L. monocytogenes-positive field. Our findings provide new data that will assist growers with science-based evaluation of their current GAPs and implementation of preventive controls that reduce the risk of preharvest contamination.