Presence of indicator bacteria, Salmonella and diarrheagenic Escherichia coli pathotypes on mung bean sprouts from public markets in Pachuca, Mexico

Rapid and simultaneous analysis of twelve virulence factor genes by a microfluidic-CFPA chip for identifying diarrheagenic Escherichia coli

An integrated microfluidic system based on circular fluorescent probe-mediated isothermal nucleic acid amplification for identification of five diarrheagenic Escherichia coli strains has been developed.

Evaluation of Grower-Friendly, Science-Based Sampling Approaches for the Detection of Salmonella in Ponds Used for Irrigation of Fresh Produce

The recognition that irrigation water sources contribute to preharvest contamination of produce has led to new regulations on testing microbial water quality. To best identify contamination problems, growers who depend on irrigation ponds need guidance on how and where to collect water samples for testing. In this study, we evaluated several sampling strategies to identify Salmonella and Escherichia coli contamination in five ponds used for irrigation on produce farms in southern Georgia. Both Salmonella and E. coli were detected regularly in all the ponds over the 19-month study period, with overall prevalence and concentrations increasing in late summer and early fall. Of 507 water samples, 217 (42.8%) were positive for Salmonella, with a very low geometric mean (GM) concentration of 0.06 most probable number (MPN)/100 mL, and 442 (87.1%) tested positive for E. coli, with a GM of 6.40 MPN/100 mL. We found no significant differences in Salmonella or E. coli detection rates or concentrations between sampling at the bank closest to the pump intake versus sampling from the bank around the pond perimeter, when comparing with results from the pump intake, which we considered our gold standard. However, samples collected from the bank closest to the intake had a greater level of agreement with the intake (Cohen's kappa statistic = 0.53; p < 0.001) than the samples collected around the pond perimeter (kappa = 0.34; p = 0.009). E. coli concentrations were associated with increased odds of Salmonella detection (odds ratio = 1.31; 95% confidence interval = 1.10-1.56). All the ponds would have met the Produce Safety Rule standards for E. coli, although Salmonella was also detected. Results from this study provide important information to growers and regulators about pathogen detection in irrigation ponds and inform best practices for surface water sampling.

Behavior of 11 Foodborne Bacteria on Whole and Cut Mangoes var. Ataulfo and Kent and Antibacterial Activities of Hibiscus sabdariffa Extracts and Chemical Sanitizers Directly onto Mangoes Contaminated with Foodborne Bacteria

The behavior of foodborne bacteria on whole and cut mangoes and the antibacterial effect of Hibiscus sabdariffa calyx extracts and chemical sanitizers against foodborne bacteria on contaminated mangoes were investigated. Mangoes var. Ataulfo and Kent were used in the study. Mangoes were inoculated with Listeria monocytogenes, Shigella flexneri, Salmonella Typhimurium, Salmonella Typhi, Salmonella Montevideo, Escherichia coli strains (O157:H7, non-O157:H7 Shiga toxin-producing, enteropathogenic, enterotoxigenic, enteroinvasive, and enteroaggregative). The antibacterial effect of five roselle calyx extracts (water, ethanol, methanol, acetone, and ethyl acetate), sodium hypochlorite, colloidal silver, and acetic acid against foodborne bacteria were evaluated on contaminated mangoes. The dry extracts obtained with ethanol, methanol, acetone, and ethyl acetate were analyzed by nuclear magnetic resonance spectroscopy to determine solvent residues. Separately, contaminated whole mangoes were immersed in five hibiscus extracts and in sanitizers for 5 min. All foodborne bacteria attached to mangoes. After 20 days at 25 ± 2°C, all foodborne bacterial strains on whole Ataulfo mangoes had decreased by approximately 2.5 log, and on Kent mangoes by approximately 2 log; at 3 ± 2°C, they had decreased to approximately 1.9 and 1.5 log, respectively, on Ataulfo and Kent. All foodborne bacterial strains grew on cut mangoes at 25 ± 2°C; however, at 3 ± 2°C, bacterial growth was inhibited. Residual solvents were not detected in any of the dry extracts by nuclear magnetic resonance. Acetonic, ethanolic, and methanolic roselle calyx extracts caused a greater reduction in concentration (2 to 2.6 log CFU/g) of all foodborne bacteria on contaminated whole mangoes than the sodium hypochlorite, colloidal silver, and acetic acid. Dry roselle calyx extracts may be a potentially useful addition to disinfection procedures of mangoes.

Antibacterial Activities of Hibiscus sabdariffa Extracts and Chemical Sanitizers Directly on Green Leaves Contaminated with Foodborne Pathogens

Leafy greens have been associated with foodborne disease outbreaks in different countries. To decrease microbial contamination of leafy greens, chemical agents are commonly used; however, a number of studies have shown these agents to have limited antimicrobial effect against pathogenic bacteria on vegetables. The objective of this study was to compare the antibacterial effect of Hibiscus sabdariffa calyx extracts (water, methanol, acetone, and ethyl acetate), sodium hypochlorite, acetic acid, and colloidal silver against foodborne bacteria on leafy greens. Thirteen foodborne bacteria were used in the study: Listeria monocytogenes, Shigella flexneri, Salmonella serotypes Typhimurium Typhi, and Montevideo, Staphylococcus aureus, Escherichia coli O157:H7, five E. coli pathotypes (Shiga toxin-producing, enteropathogenic, enterotoxigenic, enteroinvasive, and enteroaggregative), and Vibrio cholerae O1. Each foodborne bacterium was separately inoculated on romaine lettuce, spinach, and coriander leaves. Separately, contaminated leafy greens were immersed in four hibiscus extracts and in sanitizers for 5 min. Next, green leaves were washed with sterile tap water. Separately, each green leaf was placed in a bag that contained 0.1% sterile peptone water and was rubbed for 2 min. Counts were done by plate count using appropriate dilutions (in sterile peptone water) of the bacterial suspensions spread on Trypticase soy agar plates and incubated at 35 ± 2°C for 48 h. Statistically significant differences ( P < 0.05) were calculated with an analysis of variance and Duncan's test. All 13 foodborne bacteria attached to leafy greens. Roselle calyx extracts caused a significantly greater reduction ( P < 0.05) in concentration of all foodborne bacteria on contaminated romaine lettuce, spinach, and coriander than did the sodium hypochlorite, colloidal silver, and acetic acid. Dry roselle calyx extracts may potentially be a useful addition to disinfection procedures for romaine lettuce, spinach, and coriander.

Attachment of 13 Types of Foodborne Bacteria to Jalapeño and Serrano Peppers and Antibacterial Effect of Roselle Calyx Extracts, Sodium Hypochlorite, Colloidal Silver, and Acetic Acid against These Foodborne Bacteria on Peppers

Chili peppers are a very important crop in Mexico. However, these peppers have been associated with Salmonella infection outbreaks in the United States, and Salmonella and diarrheagenic Escherichia coli pathotypes have been isolated from jalapeño and serrano peppers in Mexico. To decrease microbial contamination of fruits and vegetables, chemical agents are commonly used; however, chemical agents used to eliminate pathogenic bacteria on vegetables have a limited antimicrobial effect. Roselle ( Hibiscus sabdariffa ) calyces have been reported to have an antimicrobial effect on pathogenic bacteria. In the present study, the antibacterial effect of four roselle calyx extracts (water, methanol, acetone, and ethyl acetate), sodium hypochlorite, colloidal silver, and acetic acid against foodborne bacteria was evaluated on contaminated jalapeño and serrano peppers. The 13 types of foodborne bacteria evaluated were Listeria monocytogenes , Shigella flexneri , Salmonella Typhimurium, Salmonella Typhi, Salmonella Montevideo, Staphylococcus aureus , E. coli O157:H7, five E. coli pathotypes (Shiga toxin producing, enteropathogenic, enterotoxigenic, enteroinvasive, and enteroaggregative), and Vibrio cholerae O1. All 13 types attached to both pepper types, with no significant differences in attachment between jalapeño and serrano peppers. Roselle calyx extract treatment resulted in a greater reduction in levels of all foodborne bacteria than did treatment with sodium hypochlorite, colloidal silver, and acetic acid on both pepper types. Roselle calyx extracts may be a useful for disinfection of chili peppers in the field, processing plants, restaurants, and homes.

High Occurrence Rate and Contamination Level of Bacillus cereus in Organic Vegetables on Sale in Retail Markets

Organic foods have risen in popularity recently. However, the increased risk of bacterial contamination of organic foods has not been fully evaluated. In this study, 100 samples each of organic and conventional fresh vegetables (55 lettuce samples and 45 sprout samples) sold in South Korea were analyzed for aerobic bacteria, coliforms, Escherichia coli, and Bacillus cereus. Although the aerobic bacteria and coliform counts were not significantly different between the two farming types (p > 0.05), the occurrence rate of B. cereus was higher in organically cultivated vegetables compared with those grown conventionally (70% vs. 30%, respectively). The mean contamination level of B. cereus-positive organic samples was also significantly higher (1.86 log colony-forming unit [CFU]/g vs. 0.69 log CFU/g, respectively) (p < 0.05). In addition, six samples of organic vegetables were found to be contaminated with B. cereus at over 4 log CFU/g categorized as unsatisfactory according to Health Protection Agency guideline. The relatively higher occurrence rate of B. cereus in organic vegetables emphasizes the importance of implementing control measures in organic vegetable production and postharvest processing to reduce the risk of food poisoning.

Growth of healthy and sanitizer-injured Salmonella cells on mung bean sprouts in different commercial enrichment broths

The ability of nine commercial broths to enrich healthy and 90% sanitizer-injured Salmonella Typhimurium and Salmonella cocktail on mung bean sprouts was evaluated to select an optimum broth for detection. Results showed that S. Typhimurium multiplied faster and reached a higher population in buffered peptone water (BPW), Salmonella AD media (AD) and ONE broth-Salmonella (OB), compared with other broths. Healthy and 90% sanitizer-injured Salmonella at low concentrations increased by 4.0 log CFU/ml in these three broths. However, no Salmonella growth was observed in lactose broth (LB). Further investigation showed that during incubation, pH of LB dropped from 6.7 to 4.2, due to production of lactic (66 mM) and acetic acids (62 mM) by lactic acid bacteria that were identified as dominant microbiota in bean sprouts. Though no cell membrane damage was detected by propidium monoazide combined with real-time PCR, it was found that LB inhibited Salmonella growth, especially from low inoculum levels. This study suggests that in consideration of effectiveness and cost, BPW would be a suitable enrichment broth to use for isolating and detecting Salmonella on mung bean sprouts, while using LB might cause false negative results in Salmonella detection by either PCR or standard cultural method.

Microbiological Quality of Ready-to-Eat Vegetables Collected in Mexico City: Occurrence of Aerobic-Mesophilic Bacteria, Fecal Coliforms, and Potentially Pathogenic Nontuberculous Mycobacteria

The aims of this study were to evaluate the microbiological quality and the occurrence of nontuberculous mycobacteria (NTM) in a variety of salads and sprouts from supermarkets and street vendors in Mexico City. Aerobic-mesophilic bacteria (AMB) were present in 100% of RTE-salads samples; 59% of samples were outside guidelines range (>5.17 log₁₀ CFU per g). Although fecal coliforms (FC) were present in 32% of samples, only 8% of them exceeded the permissible limit (100 MPN/g). Regarding the 100 RTE-sprouts, all samples were also positive for AMB and total coliforms (TC) and 69% for FC. Seven NTM species were recovered from 7 salad samples; they included three M. fortuitum, two M. chelonae, one M. mucogenicum, and one M. sp. Twelve RTE-sprouts samples harbored NTM, which were identified as M. porcinum (five), M. abscessus (two), M. gordonae (two), M. mucogenicum (two), and M. avium complex (one). Most RTE-salads and RTE-sprouts had unsatisfactory microbiological quality and some harbored NTM associated with illness. No correlation between the presence of coliforms and NTM was found. Overall, these results suggest that RTE-salads and RTE-sprouts might function as vehicles for NTM transmission in humans; hence, proper handling and treatment before consumption of such products might be recommendable.

Presence and correlation of some enteric indicator bacteria, diarrheagenic Escherichia coli pathotypes, and Salmonella serotypes in alfalfa sprouts from local retail markets in Pachuca, Mexico

Data on the presence of diarrheagenic Escherichia coli pathotypes (DEPs) in alfalfa sprouts and correlations between the presence of coliform bacteria (CB), fecal coliforms (FC), E. coli, DEPs, and Salmonella in alfalfa sprouts are not available. The presence of and correlations between CB, FC, E. coli, DEPs, and Salmonella in alfalfa sprouts were determined. One hundred sprout samples were collected from retail markets in Pachuca, Hidalgo State, Mexico. The presence of indicator bacteria and Salmonella was determined using conventional culture procedures. DEPs were identified using two multiplex PCR procedures. One hundred percent of samples were positive for CB, 90% for FC, 84% for E. coli, 10% for DEPs, and 4% for Salmonella. The populations of CB ranged from 6.2 up to 8.6 log CFU/g. The FC and E. coli concentrations were between , 3 and 1,100 most probable number (MPN)/g. The DEPs identified included enterotoxigenic E. coli (ETEC; 2%), enteropathogenic E. coli (EPEC; 3%), and Shiga toxin-producing E. coli (STEC; 5%). No E. coli O157:H7 strains were detected in any STEC-positive samples. In samples positive for DEPs, the concentrations ranged from 210 to 240 MPN/g for ETEC, 28 to 1,100 MPN/g for EPEC, and 3.6 to 460 MPN/g for STEC. The Salmonella isolates identified included Salmonella enterica serotype Typhimurium in three samples and Salmonella enterica serotype Enteritidis in one. STEC and Salmonella Typhimurium were identified together in one sample. Positive correlations were observed between FC and E. coli, between FC and DEPs, and between E. coli and DEPs. Negative correlations occurred between CB and DEPs and between CB and Salmonella. Neither FC nor E. coli correlated with Salmonella in the sprout samples. To our knowledge, this is the first report of ETEC, EPEC, and STEC isolated from alfalfa sprouts and the first report of correlations between different indicator groups versus DEPs and Salmonella.

Behavior of shiga toxin-producing Escherichia coli, enteroinvasive E. coli, enteropathogenic E. coli and enterotoxigenic E. coli strains on whole and sliced jalapeño and serrano peppers

The behavior of enterotoxigenic Escherichia coli (ETEC), enteropathogenic E. coli (EPEC), enteroinvasive E. coli (EIEC) and non-O157 shiga toxin-producing E. coli (non-O157-STEC) on whole and slices of jalapeño and serrano peppers as well as in blended sauce at 25 ± 2 °C and 3 ± 2 °C was investigated. Chili peppers were collected from markets of Pachuca city, Hidalgo, Mexico. On whole serrano and jalapeño stored at 25 ± 2 °C or 3 ± 2 °C, no growth was observed for EPEC, ETEC, EIEC and non-O157-STEC rifampicin resistant strains. After twelve days at 25 ± 2 °C, on serrano peppers all diarrheagenic E. coli pathotypes (DEP) strains had decreased by a total of approximately 3.7 log, whereas on jalapeño peppers the strains had decreased by approximately 2.8 log, and at 3 ± 2 °C they decreased to approximately 2.5 and 2.2 log respectively, on serrano and jalapeño. All E. coli pathotypes grew onto sliced chili peppers and in blended sauce: after 24 h at 25 ± 2 °C, all pathotypes had grown to approximately 3 and 4 log CFU on pepper slices and sauce, respectively. At 3 ± 2 °C the bacterial growth was inhibited.

Presence of Shiga toxin-producing Escherichia coli, Enteroinvasive E. coli, Enteropathogenic E. coli, and Enterotoxigenic E. coli on tomatoes from public markets in Mexico

Diarrheagenic Escherichia coli pathotypes (DEP) are important foodborne pathogens in various countries, including Mexico. However, no data exist on the presence of DEP on fresh tomatoes (Solanum lycopericum) from Mexico. The frequency of fecal coliforms (FC), E. coli, and DEP were determined for two tomato varieties. One hundred samples of a saladette tomato variety and 100 samples of a red round tomato variety were collected from public markets in Pachuca, Mexico. Each tomato sample consisted of four whole tomatoes. For the 100 saladette samples, coliform bacterial, FC, E. coli, and DEP were identified in 100, 70, 60, and 10% of samples, respectively. For the 100 red round samples, coliform bacterial, FC, E. coli, and DEP were identified in 100, 75, 65, and 11% of samples, respectively. Identified DEP included Shiga toxin-producing E. coli (STEC), enteroinvasive E. coli (EIEC), enteropathogenic E. coli (EPEC), and enterotoxigenic E. coli (ETEC). STEC were isolated from 6% of saladette samples and 5% of red round samples. ETEC were isolated from 3% of saladette samples and 4% of red round samples. EPEC were isolated from 2% of saladette samples and 3% of red round samples, and EIEC were isolated from 1% of saladette samples. Both STEC and ETEC were identified in two saladette samples and 1 red round sample. E. coli O157:H7 was not detected in any STEC-positive samples.

Behavior of non-O157 Shiga toxin-producing Escherichia coli, enteroinvasive E. coli, enteropathogenic E. coli, and enterotoxigenic E. coli strains on alfalfa sprouts

Data about the behavior of non-O157 Shiga toxin-producing Escherichia coli (non-O157 STEC), enteroinvasive E. coli (EIEC), enterotoxigenic E. coli (ETEC), and enteropathogenic E. coli (EPEC) on seeds and alfalfa sprouts are not available. The behavior of STEC, EIEC, ETEC, and EPEC was determined during germination and sprouting of alfalfa seeds at 20 ± 2°C and 30 ± 2°C and on alfalfa sprouts at 3 ± 2°C. When alfalfa seeds were inoculated with STEC, EIEC, ETEC, or EPEC strains, all these diarrheagenic E. coli pathotypes (DEPs) grew during germination and sprouting of seeds, reaching counts of approximately 5 and 6 log CFU/g after 1 day at 20 ± 2°C and 30 ± 2°C, respectively. However, when the sprouts were inoculated after 1 day of seed germination and stored at 20 ± 2°C or 30 ± 2°C, no growth was observed for any DEP during sprouting at 20 ± 2°C or 30 ± 2°C for 9 days. Refrigeration reduced significantly (P < 0.0.5) the number of viable DEPs on sprouts after 20 days in storage; nevertheless, these decreases have no practical significance for the safety of the sprouts.