Salmonella Typhimurium Infections Transmitted by Chlorine-pretreated Clover Sprout Seeds

Food-borne disease outbreaks linked to the consumption of raw sprouts have become a concern over the past decade. A Monte Carlo simulation model of the sprout production process was created to determine the most-effective points for pathogen control. Published literature was reviewed, and relevant data were compiled. Appropriate statistical distributions were determined and used to create the Monte Carlo model with Analytica software. Factors modeled included initial pathogen concentration and prevalence, seed disinfection effectiveness, and sampling of seeds prior to sprouting, sampling of irrigation water, or sampling of the finished product. Pathogen concentration and uniformity of seed contamination had a large effect on the fraction of contaminated batches predicted by the simulation. The model predicted that sprout sampling and irrigation water sampling at the end of the sprouting process would be more effective in pathogen detection than seed sampling prior to production. Day of sampling and type of sample (sprout or water) taken had a minimal effect on rate of detection. Seed disinfection reduced the proportion of contaminated batches, but in some cases it also reduced the ability to detect the pathogen when it was present, because cell numbers were reduced below the detection limit. Both the amount sampled and the pathogen detection limit were shown to be important variables in determining sampling effectiveness. This simulation can also be used to guide further research and compare the levels of effectiveness of different risk reduction strategies.Seeds and bean sprouts have become a serious food safety concern during the past decade. Outbreaks of salmonellosis and food-borne illness from pathogenic Escherichia coli have been linked with contaminated sprouts. These outbreaks have been most commonly associated with alfalfa sprouts but have also been linked to clover, radish, and mung bean sprouts.

Section: Methodsmentioning

confidence: 99%

Monte Carlo Simulation of Pathogen Behavior during the Sprout Production Process

Montville

Schaffner

2005

“…Interestingly, strains that were serotyped as Newport by PFGE in the prior study were frequently MDR, while no MDR Newport strains were identified by rep-PCR in our study. Montevideo and Newport have been identified in several multistate outbreaks associated with fresh produce (4,6,37,49), while Hadar was more associated with meat or poultry (50,51). Strains with genetic similarity to serotypes Saintpaul, Braenderup, Thompson, and Javiana have also been recovered in produce-related outbreaks (6,42,(52)(53)(54), and Javiana is the most commonly reported serotype for salmonellosis in Florida (Carina Blackmore, Florida Department of Health, personal communication).…”

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.

“…Epidemiological evidence suggests that this sanitation protocol may prevent some, but not all, outbreaks (2,5), and experimental sanitation of naturally contaminated alfalfa seeds did not eliminate S. enterica from the seeds (23). To date, no seed sanitation method has been shown to eliminate S. enterica or E. coli O157:H7 from laboratory-contaminated seeds (4,13,14,19,24,25).…”

mentioning

confidence: 99%

Differences in Growth of Salmonella enterica and Escherichia coli O157:H7 on Alfalfa Sprouts

Charkowski

Barak

Sarreal

et al. 2002

112

Sprout producers have recently been faced with several Salmonella enterica and Escherichia coli O157:H7 outbreaks. Many of the outbreaks have been traced to sprout seeds contaminated with low levels of human pathogens. Alfalfa seeds were inoculated with S. enterica and E. coli O157:H7 strains isolated from alfalfa seeds or other environmental sources and sprouted to examine growth of these human pathogens in association with sprouting seeds. S. enterica strains grew an average of 3.7 log 10 on sprouting seeds over 2 days, while E. coli O157:H7 strains grew significantly less, an average of 2.3 log 10 . The initial S. enterica or E. coli O157:H7 inoculum dose and seed-sprouting temperature significantly affected the levels of both S. enterica and E. coli O157:H7 on the sprouts and in the irrigation water, while the frequency of irrigation water replacement affected only the levels of E. coli O157:H7. Colonization of sprouting alfalfa seeds by S. enterica serovar Newport and E. coli O157:H7 strains transformed with a plasmid encoding the green fluorescent protein was examined with fluorescence microscopy. Salmonella serovar Newport colonized both seed coats and sprout roots as aggregates, while E. coli O157:H7 colonized only sprout roots.Sprout producers in North America, Asia, and Europe have faced numerous Salmonella enterica and Escherichia coli O157:H7 outbreaks since 1995 (2, 17). Several of the outbreaks were traced to sprouts grown from seeds contaminated with low levels of human pathogens (2,15,19,20,27).As a result of the many recent outbreaks traced to sprouts and guidance by a U.S. Food and Drug Administration document (2), many producers now sanitize their sprout seeds with 20,000 ppm of calcium hypochlorite before sprouting and test each crop of sprouts for S. enterica and E. coli O157:H7. Epidemiological evidence suggests that this sanitation protocol may prevent some, but not all, outbreaks (2, 5), and experimental sanitation of naturally contaminated alfalfa seeds did not eliminate S. enterica from the seeds (23). To date, no seed sanitation method has been shown to eliminate S. enterica or E. coli O157:H7 from laboratory-contaminated seeds (4,13,14,19,24,25). In addition, the recommended calcium hypochlorite method does not kill or remove all naturally occurring nonpathogenic bacteria from alfalfa seeds, suggesting that bacteria on seeds may be in locations inaccessible to calcium hypochlorite treatment (7).Sprouts present an unusual food safety predicament compared to other fresh produce because bacteria, including S. enterica and E. coli O157:H7, may multiply by several logs on the sprouting seeds during the first few days of germination (1,22,23). Experiments with radish and alfalfa sprouts grown from laboratory-contaminated seeds have demonstrated that human pathogens may be present between plant cells inside sprouts, where they can resist decontamination treatments (9, 12). Washing sprouts in water only slightly reduces the number of bacteria found on the sprouts, and green sprouts are usuall...