Evaluating gulls as potential vehicles of Salmonella enterica serotype Newport (JJPX01.0061) contamination of tomatoes grown on the eastern shore of Virginia.

Salmonella enterica serovar Newport pattern JJPX01.0061 has been identified as causing several multistate outbreaks in the last 10 years, primarily due to contamination of tomatoes grown in Virginia. The goal of this study was to evaluate gulls as a potential vehicle of S. Newport pattern 61 contamination for tomatoes grown on the Eastern Shore of Virginia. Gull fecal samples were collected at four sites in eastern Virginia for 3 months (May to July) in 2012, resulting in 360 samples, among which Salmonella was isolated from 62 samples. Twenty-two serotypes and 26 pulsed-field gel electrophoresis DNA fingerprint patterns, including S. Newport pattern 61, were identified. All of the patterns that were isolated multiple times, with the exception of S. Newport patterns JJPX01.0030 and JJPX01.0061, were clustered in time and geographical location. These results strongly suggest that both patterns of S. Newport are endemic to sites on the Eastern Shore where gulls were sampled. This study provides additional information regarding the epidemiology of S. Newport pattern 61 in Virginia and how tomatoes sold interstate may become contaminated in the field.

Salmonella population rebound and its prevention on spray washed and non-washed jalapeño peppers and roma tomatoes in humid storage.

The potential of Salmonella population to rebound on non-washed and washed roma tomatoes and jalapeño peppers in humid storage at 4°C, 10°C, 15°C, 21°C, or 35°C for ≤12 days was investigated. The initial inoculation levels of Salmonella on peppers and tomatoes were 5.6 and 5.2 log CFU/cm(2), respectively. Air-drying of fruit surfaces resulted in contamination levels of 3.9 and 3.7 log CFU/cm(2) on inoculated peppers and tomatoes, respectively. At 21°C and 35°C, the levels of air-dried Salmonella inoculums on produce surfaces increased ≥2 log cycles, with the most rapid growth in the first 3 days. Mechanical washing on rollers (rinsing; R-treatment) or revolving brushes (rinsing and brushing; RB-treatment) with water decreased Salmonella counts by ≥2.5 log CFU/cm(2) on both peppers and tomatoes. After R- or RB-treatment, peppers stored at 21°C and 35°C permitted residual Salmonella (≤1.4 log CFU/cm(2)) to grow to 2.6-3.9 log CFU/cm(2). During storage, residual Salmonella (≤1.0 log CFU/cm(2)) on washed tomatoes increased to 3.1 log CFU/cm(2) at 35°C following R-treatment and 3.8 log CFU/cm(2) at 21°C following RB-treatment. Cold storage at 4°C and 10°C effectively prevented the proliferation of Salmonella on both washed and non-washed produce. The current study on jalapeño peppers and roma tomatoes demonstrated that Salmonella population can rebound on produce in humid storage before or after washing. The finding highlights the benefit of uninterrupted cold storage for safer produce operations.

Spray washing of tomatoes with chlorine dioxide to minimize Salmonella on inoculated fruit surfaces and cross-contamination from revolving brushes.

Chlorine dioxide (ClO(2)) is an antimicrobial agent available for commercial produce washing. This study examined the efficacy of ClO(2) at 5 parts per million (ppm) during spray washing of tomatoes (5.0 ml/s per fruit) for preventing Salmonella enterica transfer from inoculated roller brushes to fruit and wash runoff. Furthermore, the sanitizing effects of ClO(2) during spray washing at low and high flow rates (5.0 and 9.3 ml/s per fruit, respectively) on tomato surfaces (nonstem scar areas) with either newly introduced (wet) or overnight air-dried Salmonella inocula were investigated. Salmonella transfer from contaminated brushes to fruit surfaces was reduced 2.1 +/- 0.6 or 4.7 +/- 0.2 log cycles after spray washing with water for 40 s or with the ClO(2) solution for 10 s, respectively. Cross-contamination of Salmonella from brushes to wash runoff during fruit washing for 60 s decreased 5.9 +/- 0.3 log cycles when ClO(2) was used. Fruit washing using contaminated brushes and low flow-rate washing with either water or ClO(2) solution for 10 s reduced newly introduced Salmonella on fruit surfaces by 1.7 +/- 0.6 or 5.1 +/- 0.3 log cycles, respectively. For fruit surfaces with air-dried inocula, washing with water and using uncontaminated brushes for 10 to 40 s reduced Salmonella by 3.2 +/- 0.3 to 3.4 +/- 0.4 log cycles; and the reduction was significantly improved by using ClO(2), high flow rate, or a longer washing time. Washing with ClO(2) at tested flow rates for 10 to 60 s resulted in a 4.4 +/- 0.6 to 5.2 +/- 0.1 log reduction of air-dried Salmonella on fruit surfaces.

Evaluation of quantitative recovery methods for Listeria monocytogenes applied to stainless steel.

The ability of Listeria monocytogenes to attach to various food contact surfaces, such as stainless steel, polypropylene, and rubber compounds, is well documented. The retention of these or other pathogenic bacteria on food contact surfaces increases the risk of transmission to food products. The objective of this study was to compare several methods for quantitative recovery of Listeria monocytogenes from stainless steel surfaces. A cocktail of 4 serotypes of Listeria monocytogenes mixed in equivalent concentrations was inoculated onto type 304 stainless steel coupons in a 2 x 2 cm area. After 1 h exposure, coupons were sampled by one of the following methods: (1) swabbing with a premoistened Dacron swab; (2) rinsing with phosphate-buffered saline; (3) direct contact onto tryptic soy agar containing 0.6% yeast extract (TSA + YE) plates for 10 s; (4) sonication in an ultrasonic water bath (40 kHz); (5) contact with the bristles of a sonicating brush head for 1 min; and (6) indirect contact (2-4 mm distance) with a sonicating brush head for 1 min. The 3 sonication methods yielded higher recovery than the other 3 methods (P < 0.05). Brushing the coupons with the sonicating brush head (contact or noncontact) yielded a recovery level of about 60%. The lowest cell recovery (about 20%) was observed with the swab and direct agar contact methods. After a 12 h exposure, recoveries ranged from 17.4 (brush contact method) to 2% (swab method).

Evaluation of Microbial Loads on Dried and Fresh Shiitake Mushrooms (Lentinula edodes) as Obtained from Internet and Local Retail Markets, Respectively.

Consumer demand for shiitake mushrooms is increasing. However, food safety information regarding the prevalence of microbial pathogens on the products sold via the Internet or at local retail markets is limited. The present study was conducted to assess the microbial load on shiitake mushrooms sold through the Internet and at local (central Virginia) retail markets. A total of 90 shiitake mushroom products, consisting of locally-purchased whole (LW) and sliced (LS) and Internet-procured whole (IW), sliced (IS), and powdered (IP) forms, were tested. High levels of aerobic mesophiles (6.9 ± 1.3 to 7.5 ± 1.1 log CFU/g), yeast and mold (5.8 ± 0.9 to 6.0 ± 0.3 log CFU/g), and coliforms (1.6 ± 1.0 to 1.9 ± 1.1 log MPN/g) were found in locally-acquired mushrooms. One LW sample and 2 of LS contained Listeria spp. Our findings suggest that shiitake mushroom producers and retailers need to be aware of potential microbial hazards associated with handling fresh shiitake mushrooms and consumers should take appropriate precautions when handling fresh shiitake mushrooms to prevent cross-contamination and possible foodborne illness in the home.

Comparison of the Microbial Quality of Lamb and Goat Meat Acquired from Internet and Local Retail Markets.

This study was conducted to evaluate the microbial quality of lamb and goat meat sold through local (Virginia) and Internet (U. S.) retail markets. A total of 134 frozen meat products consisting of locally purchased lamb ground (LLG) and lamb chops and Internet-procured lamb ground, goat ground, lamb chops (ILC), goat chops (IGC), lamb stew, and goat stew were tested. Significantly higher levels of aerobic mesophiles, psychrotrophs, and coliforms were found in the meat locally acquired than in the meat procured from the Internet. Similar average prevalence (27%) of Escherichia coli was observed regardless of market source. Ground meat had significantly high levels and prevalence of mesophiles, psychrotrophs, coliforms, and Listeria spp. One sample of LLG contained Campylobacter, and one sample of IGC contained Salmonella. Listeria spp. were present in 23 to 40% and 17 to 80% of samples from local and Internet markets, respectively. Pulsed-field gel electrophoresis (PFGE) of isolated E. coli strains revealed brand specificity and genomic diversity. No isolate from different brands and market sources had matching PFGE profiles. The average price of Internet meat ($23.4/kg) was about 1.2 times higher than the price of local meat, except for ILC, whose price was 2.7 times higher. This study revealed differences in microbial quality of lamb and goat meat based on market source; thus, meat products should be handled carefully regardless of market source because of the presence of high microbial levels and the high prevalence of pathogens.

Utilization of fluorogenic assay for rapid detection of Escherichia coli in acidic fruit juice.

This study was undertaken to investigate interference by acids commonly found in fruit juice in Escherichia coli assays involving the use of 4-methylumbelliferyl-beta-D-glucuronide (MUG) as a fluorogenic substrate for enzyme reaction. Fluorescence intensity was negatively correlated (P < 0.001) with the volume of fresh citrus juice tested by the lauryl tryptose broth (LST)-MUG assay, and the permissible sample sizes were limited to 0.3 and 0.5 ml for fresh citrus juices with pHs of 3.3 and 3.9, respectively. In addition, false-negative results were visually observed under UV light when the E*Colite assay was used to test large volumes (5 to 10 ml per test) of fresh citrus juice or when the test broth used for the LST-MUG assay was supplemented with citric, malic, or tartaric acid at 2 to 4 g/liter. These results suggest that the size and pH of acidic samples should be controlled in MUG-based fluorogenic assays. The inhibitory effect on fluorescence was due to high acidity, which reduces fluorescence from 4-methylumbelliferone. Buffering improved the assays. When sodium bicarbonate was incorporated in the enrichment broth at 10 g/liter, the permissible sample sizes for fresh grapefruit juice (pH 3.1) increased from 0.3 to 1 ml for the LST-MUG (with 9.9 ml of broth) assay and from 3 to 10 ml for the E*Colite (with 99 ml of broth) assay.

Growth of Salmonella enterica and Staphylococcus aureus in no-knead bread dough during prolonged yeast fermentation.

A convenient bread making method involving prolonged fermentation of no-knead (nonkneaded) dough has become popular in recent years. In the present study, the microbial safety of no-knead dough made with a 375:325:5:1 weight ratio of flour, water, salt, and bread yeast was investigated. Three brands of dehydrated yeast were used for this study. The growth of inoculated Salmonella enterica and Staphylococcus aureus in no-knead dough during fermentation was significant (P<0.05), regardless of yeast brand. The multiplication rates of S. enterica in the initial 12 h and S. aureus over the entire 24 h of fermentation were positively correlated with fermentation temperatures of 21 to 38°C (P<0.005; r≥0.996). Mean counts of S. enterica increased by 0.5, 1.5, 1.9, and 2.4 log CFU/g, respectively, after 6, 12, 18, and 24 h of fermentation at 21 °C. The level of S. aureus increased by 0.4, 1.1, 1.7, and 2.2 CFU/g, respectively, after 18 h of fermentation at 21, 27, 32, and 38 °C. Because prolonged fermentation permits substantial growth of infectious and/or toxin-producing foodborne pathogens, the making of slow-rise, no-knead bread may compromise consumer kitchen sanitation and food safety.

Detection of Salmonella strains and Escherichia coli O157:H7 in feces of small ruminants and their isolation with various media.

Salmonella strains and Escherichia coli O157:H7 were detected in 17 and 5 small ruminants in Virginia, respectively, of 287 tested. Background microflora interfered with the fecal analysis. The combination of Salmonella enzyme immunoassay (EIA) detection and xylose-lysine-deoxycholate agar isolation was satisfactory. Modifying enrichment to a 1:100 dilution enabled effective E. coli O157:H7 detection by EIA and isolation by sorbitol-MacConkey agar with cefixime-tellurite.