Cross-sectional survey of indicator and pathogenic bacteria on vegetables sold from Asian vendors at farmers' markets in northern California

Pathogenic Microorganisms Linked to Fresh Fruits and Juices Purchased at Low-Cost Markets in Ecuador, Potential Carriers of Antibiotic Resistance

The pathogenic microorganisms linked to fresh fruits and juices sold out in retail low-cost markets raise safety concerns as they may carry multidrug-resistant (MDR) genes. To evaluate the microbiological quality and safety of highly consumed fruits and derivatives in Imbabura Province, Ecuador, ready-to-eat strawberries (5 independent batches; n = 300 samples), and gooseberries (5 separate batches; n = 500 samples), purchased from a local fruit farm grower and low-cost retail market, along with 20 different natural fruit- and vegetables-based juices (3 independent batches; n = 60 samples) purchased from food courts located within the low-cost markets were analyzed. Bacteriological analysis showed that the microbial quality was lower as several indicators (n = 984) consisting of total coliforms (TCOL), total aerobes (AEROB), Enterobacter spp. (ENT), Shigella spp., (SHIGA), yeasts (YE), and molds (M) were detected. Staphylococcus spp. (STAPHY) was found in both fruits regardless of origin, while Escherichia coli (EC) isolates were found in strawberries but not gooseberries. Salmonella spp. (SALM) were detected in juices only. Antibiotic susceptibility testing showed multidrug resistance of several isolates. The hemolytic pattern revealed that 88.89% of EC and 61.11% of ENT isolates were beta-hemolytic. All STAPHY isolates were beta-hemolytic while SALM and SHIGA were alpha-hemolytic. Plasmid curing assay of MDR isolates (ENT, EC, SALM, and STAPHY) showed that the antibiotic resistance (AR) was highly indicative of being plasmid-borne. These results raise concerns about the consumption of MDR bacteria. However, good agricultural and industrial practices, behavioral change communication, and awareness-raising programs are necessary for all stakeholders along the food production and consumption supply chain.

The antimicrobial interventions of cilantro (Coriandrum sativum) in mitigating cross-contamination of foodborne pathogens during the retail soaking process

The efficacy of commercially available antimicrobials for fresh produce, electrolyzed water (EW; ca. 60 mg/L of free chlorine), a combination of lactic acid and phosphoric acid-based (LPA), and citric acid-based (CA) was compared with tap water (TW) in preventing cross-contamination during the soaking step of crisping at a retail setting. A bunch of cilantro (103.7 ± 14.9 g/bunch) was inoculated with 3-strain cocktail of nalidixic acid-resistant Salmonella enterica and E. coli O157:H7, S. enterica and Listeria monocytogenes, or E. coli O157:H7 and L. monocytogenes (ca. 5.0 log CFU/g). One inoculated and seven non-inoculated cilantro bunches were soaked in 76 L of TW, EW, LPA, and CA for five minutes. Two additional soakings, each with eight bunches of non-inoculated cilantro were performed in the same soaking water. To determine the cross-contamination of inoculated foodborne pathogens via soaking water, the cilantro samples and soaking water following each soaking step were subjected to microbiological analyses using selective media supplemented with nalidixic acid (100 μg/mL). During the first soaking, significantly greater reductions in Salmonella (2.9 ± 0.5 log CFU/g), E. coli O157:H7 (3.0 ± 0.1), and L. monocytogenes (2.7 ± 0.3) on cilantro were achieved with EW compared to soaking with TW, LPA, and CA (P < 0.05). Cross-contamination of foodborne pathogens from inoculated cilantro to non-inoculated cilantro was completely mitigated by EW during three subsequent soaking events. With the exception of TW soaking water, no inoculated foodborne pathogens were detected in the 100 mL soaking water of EW, CA, and LPA collected. Including an appropriate concentration of chemical antimicrobial in water during the soaking step of crisping aids in mitigating cross-contamination of foodborne pathogen(s) in cilantro bunches.

Detection and analysis of indicator and pathogenic bacteria in conventional and organic fruits and vegetables sold in retail markets

Produce-associated foodborne outbreaks have been increasingly implicated as the significant proportion of the annual incidence of foodborne illness worldwide. The objectives of this study were to determine the concentrations of indicator bacteria and the presence of Salmonella spp., Shigella spp., Escherichia coli O157:H7, and Listeria monocytogenes, and to characterize predictors associated with Salmonella contamination of retail produce from fresh markets and supermarkets in Bangkok, Thailand. A total of 503 samples were collected during May 2018 and February 2019, comprised of sweet basil, spring onion, coriander, cabbage, lettuce, cucumber, and tomato, with n = 167 conventional items from fresh open-air markets, n = 168 conventional items from supermarkets, and n = 168 organic items from supermarkets. The overall prevalence in these 503 items for fecal coliforms and E. coli were 84.3% and 71.4%, with mean concentrations (± S.D.) of fecal coliforms and E. coli being 3.0×105 (± 1.3×106) and 1.8×105 (± 1.1×105) MPN/g, respectively. The concentration of fecal coliforms and E. coli was higher in produce sampled from fresh open-air markets than produce from supermarkets; similarly, these bacterial indicators were higher from produce grown under conventional methods than certified organic produce. The prevalence of Salmonella and Shigella was 4.8% and 0.4%, respectively, but no positives were found for E. coli O157:H7 and L. monocytogenes. The predominant Salmonella serovar were Stanley (30.8%). Based on logistic regression, the odds of Salmonella contamination were significantly (p < 0.05) higher during the rainy versus dry season, produce grown using conventional versus organic agriculture, sweet basil versus other commodities, and using ice tank versus dry refrigeration for overnight retail storage. This study indicated that fruits and vegetables are important sources of microbial contamination. Hence, monitoring and surveillance of pathogen contamination to produce is needed to strengthen food safety.

Survival and Persistence of Foodborne Pathogens in Manure-Amended Soils and Prevalence on Fresh Produce in Certified Organic Farms: A Multi-Regional Baseline Analysis

Biological soil amendments of animal origin (BSAAOs), including untreated (e.g., raw or aged manure, or incompletely composted manure) and treated animal products (e.g., compost), are used for crop production and as part of soil health management. Application of BSAAO's must be done cautiously, as raw manure commonly contains enteric foodborne pathogens that can potentially contaminate edible produce that may be consumed without cooking. USDA National Organic Program (NOP) certified production systems follow the 90-or 120-day interval standards between applications of untreated BSAAOs and crop harvest, depending on whether the edible portions of the crops are in indirect or direct contact with the soil, respectively. This study was conducted to evaluate the survival of four foodborne pathogens in soils amended with BSAAOs and to examine the potential for bacterial transfer to fresh produce harvested from USDA NOP certified organic farms (19) from four states. Only 0.4% (2/527) of produce samples were positive for L. monocytogenes. Among the untreated manure and compost samples, 18.0% (42/233) were positive for at least one of the tested and culturable bacterial foodborne pathogens. The prevalence of non-O157 STEC and Salmonella in untreated manure was substantially > that of E. coli O157:H7 and L. monocytogenes. Of the 2,461 soil samples analyzed in this study, 12.9% (318) were positive for at least one pathogen. In soil amended with untreated manure, the prevalence of non-O157 STEC [7.7% (190) and L. monocytogenes (5.0% (122), was > that of Salmonella (1.1% (26)] or E. coli O157 [0.04% (1)]. Foodborne pathogen prevalence in the soil peaked after manure application and decreased significantly 30 days post-application (dpa). However, non-O157 STEC and L. monocytogenes were recovered from soil samples after 90 and 120 dpa. Results indicate that produce contamination by tested foodborne pathogens was infrequent, but these data should not be generalized outside of the specific wait-time regulations for organic crop production and the farms studied. Moreover, other sources of contamination, e.g., irrigation, wildlife, environmental conditions, cropping and management practices, should be considered. This study also provides multi-regional baseline data relating to current NOP application intervals and development of potential risk mitigation strategies to reduce pathogen persistence in soils amended with BSAAOs. These findings contribute to filling critical data gaps concerning occurrence of fecal pathogens in NOP-certified farming systems used for production of fresh produce in different US regions.

Cross-Contamination on Atypical Surfaces and Venues in Food Service Environments

ABSTRACT

Cross-contamination of raw food to other surfaces, hands, and foods is a serious issue in food service. With individuals eating more meals away from home, contracting a foodborne illness from a food service establishment is an increasing concern. However, most studies have concentrated on hands or food contact surfaces and neglected atypical and unusual surfaces (surfaces that are not typically identified as a source of cross-contamination) and venues. This review was conducted to identify atypically cross-contaminated surfaces and atypical venues where cross-contamination could occur that have not been examined thoroughly in the literature. Most surfaces that could be at risk for cross-contamination are frequently touched, are rarely cleaned and sanitized, and can support the persistence and/or growth of foodborne pathogens. These surfaces include menus, spice and condiment containers, aprons and coveralls, mobile devices and tablets, and money. Venues that are explored, such as temporary events, mobile vendors, and markets, are usually limited in space or infrastructure, have low compliance with proper hand washing, and provide the opportunity for raw and ready-to-eat foods to come into contact with one another. These factors create an environment in which cross-contamination can occur and potentially impact food safety. A more comprehensive cleaning and sanitizing regime encompassing these surfaces and venues could help mitigate cross-contamination. This review highlights key surfaces and venues that have the potential to be cross-contaminated and have been underestimated or not fully investigated. These knowledge gaps indicate where further work is needed to fully understand the role of these surfaces and venues in cross-contamination and how it can be prevented.

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AmpC- and Extended-Spectrum β-Lactamase-Producing Enterobacteriaceae Detected in Fresh Produce in Central Ohio

ABSTRACT

Salad vegetables purchased from farmer's markets and grocery stores in central Ohio during the summers of 2015 and 2016 were tested for the presence of Enterobacteriaceae resistant to extended-spectrum cephalosporins and carbapenems, Salmonella contamination, and coliform bacterial counts. A total of 364 samples were collected from 36 farmers' markets and 33 grocery stores. Using selective media, we found 23 (6.3%) samples that produced Enterobacteriaceae expressing an AmpC β-lactamase phenotype, with 11 (3.0%) confirmed to contain blaCMY and 6 (1.6%) that produced Enterobacteriaceae with an extended-spectrum β-lactamase (ESBL) phenotype, 1 (0.3%) of which was confirmed to contain blaCTX-M. All blaCMY and blaCTX-M strains were isolated from leafy greens. No Salmonella spp. or carbapenem-resistant Enterobacteriaceae were recovered from fresh produce samples. Adjusting for year, the geometric mean coliform count differed (P < 0.05) between produce types, with the count in tomatoes (15 CFU/mL) being lower than those in cucumbers (77.4 CFU/mL) and leafy greens (75.0 CFU/mL). The coliform counts also differed (P < 0.05) between years, with 19.6 CFU/mL in 2015 and 96.0 CFU/mL in 2016. There was no difference in coliform counts or the prevalences of Enterobacteriaceae expressing AmpC or ESBL phenotypes in produce purchased from farmers' markets and grocery stores.

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Salmonella and Escherichia coli Prevalence in Meat and Produce Sold at Farmers' Markets in Northern California

ABSTRACT

As the number of farmers' markets and other direct-to-consumer marketing channels increases, it is crucial to understand the potential risks associated with consuming directly marketed animal products and fresh produce. The overall aim of this project was to assess the prevalence of Salmonella and Escherichia coli in animal products and produce sold at farmers' markets in Northern California and to evaluate the food safety risks associated with consuming meat (e.g., beef, pork, and poultry) and fresh produce purchased from farmers' markets. Animal products and produce were purchased from a total of 44 certified farmers' markets in Northern California. Salmonella was found in 6 (1.8%) of 338 animal products and in 0 (0%) of 128 produce samples; E. coli was found in 40 (31.3%) of 128 fresh produce samples. E. coli concentration in produce ranged from 0 to 2.96, with an overall average of 0.13 log (most probable number + 1)/100 mL. Salmonella isolates were resistant to nalidixic acid and tetracycline. The results from this study highlight the need for further training on mitigation strategies to reduce contamination of animal products and fresh produce by foodborne pathogens.

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Modelling of Indicator Escherichia coli Contamination in Sentinel Oysters and Estuarine Water

This study was performed to improve the ability to predict the concentrations of Escherichia coli in oyster meat and estuarine waters by using environmental parameters, and microbiological and heavy metal contamination from shellfish growing area in southern Thailand. Oyster meat (n = 144) and estuarine waters (n = 96) were tested for microbiological and heavy metal contamination from March 2016 to February 2017. Prevalence and mean concentrations of E. coli were 93.1% and 4.6 × 10³ most probable number (MPN)/g in oyster meat, and 78.1% and 2.2 × 10² MPN/100 mL in estuarine water. Average 7-day precipitation, ambient air temperature, and the presence of Salmonella were associated with the concentrations of E. coli in oyster meat (p < 0.05). Raw data (MPN/g of oyster meat and MPN/100 mL of estuarine water) and log-transformed data (logMPN/g of oyster meat and logMPN/100 mL of estuarine water) of E. coli concentrations were examined within two contrasting regression models. However, the more valid predictions were conducted using non-log transformed values. These findings indicate that non-log transformed data can be used for building more accurate statistical models in microbiological food safety, and that significant environmental parameters can be used as a part of a rapid warning system to predict levels of E. coli before harvesting oysters.

Spatial and temporal variability of bacterial indicators and pathogens in six California reservoirs during extreme drought

California has one of the largest systems of surface water reservoirs in the world, providing irrigation water to California's agriculturally productive Central Valley. Irrigation water is recognized as a vehicle for the microbial contamination of raw produce and must be monitored according to new federal regulation. The purpose of this study was to further understanding of the variability of fecal indicator bacteria (Escherichia coli and fecal coliforms) and pathogens (E. coli O157:H7 (O157), non-O157 Shiga toxin-producing E. coli (STEC) and Salmonella) along both horizontal and vertical profiles within California reservoirs. Monthly sampling was conducted in six reservoirs located in the foothills of the Western Sierra Nevada during the summer irrigation season and extreme drought conditions of 2014 (n = 257). Concentrations of fecal indicator bacteria were highly variable between reservoirs (p < 0.05) and along the horizontal profile (p < 0.001) from upstream to downstream, with higher concentrations typically found outside of the reservoirs than within. Though many of the reservoirs were thermally stratified, bacterial concentrations were not associated with water temperature (p > 0.05) or any one particular depth strata (p < 0.05). However, prevalence of Salmonella and STEC (16/70 and 9/70 respectively) was higher in the deep strata than in mid or surface layers. We found no statistical association between samples collected downstream of reservoirs and those from the reservoirs themselves. Continued monitoring and modeling of both bacterial indicators and enteric pathogens are critical to our ability to estimate the risk of surface irrigation water supplies and make appropriate management decisions.

Microbiological quality of fresh produce obtained from retail stores on the Eastern Shore of Maryland, United States of America

The aim of this study was to investigate the microbiological quality of six types of fresh produce obtained from three retail stores located on the Eastern Shore of Maryland, USA. A total of 414 samples representing basil, cilantro, lettuce, scallion, spinach, and parsley were analyzed for total aerobic bacteria (APC), total coliforms, Escherichia coli, and three pathogenic bacteria (E. coli O157:H7, Listeria monocytogenes, and Salmonella), using standard methods. Presumptive pathogenic isolates were confirmed using BAX Polymerase Chain Reaction. Total aerobic populations varied widely between samples, while 38.41% were positive for total coliforms and only 10.15% for E. coli. Median abundance (log CFU/g) of total coliforms and E. coli were less than the limit of detection and that of APC ranged from 5.78 to 6.61 over the six produce types. There was a statistically significant difference in prevalence of total coliforms among the retail stores, but not for abundance of APC or prevalence of E. coli. E. coli O157:H7 and L. monocytogenes were detected in one spinach sample each, while one parsley and one cilantro sample were positive for Salmonella. There were no statistically significant differences in microbiological quality among produce types. Although the results of this study provided some indices of sanitary and/or spoilage level, no relationship was observed among the total aerobic bacteria, total coliforms, E. coli, and the presence of pathogenic bacteria in the samples tested.