Estimation of Bacteriophage MS2 Inactivation Parameters During Microwave Heating of Frozen Strawberries.

Frozen berries have been repeatedly linked to acute gastroenteritis caused by norovirus, the most common cause of foodborne illness in the United States. Many guidelines recommend that frozen berries be microwaved for at least 2 min, but it is unclear if this thermal treatment is effective at inactivating norovirus. The objective of this study was to model the effect of microwave heating at varying power levels on the survival of bacteriophage MS2, a norovirus surrogate, when inoculated onto frozen strawberries. Bacteriophage MS2 was inoculated onto the surface of frozen strawberries with a starting concentration of approximately 10 log PFU/g. Samples (either 3 or 5 whole strawberries) were heated in a 1300-Watt domestic research microwave oven (frequency of 2450 MHz) at power levels of 30, 50, 70, and 100% (full power), for times ranging from 15 to 300 s to determine inactivation. Temperatures at berry surfaces were monitored during heating using fiberoptic thermometry. All experiments were conducted in triplicate. The primary model for thermal inactivation was a log-linear model of logN vs. time. The secondary model was for a D-value decreasing linearly with temperature and an added term that was path-dependent on the thermal history. Parameters in the model were estimated using dynamic temperature history at the surface of the berry, via nonlinear regression using all data simultaneously. The root mean square error was ∼0.5 PFU/g out of a total 6-log reduction. Log reductions of 1.1 ± 0.4, 1.5 ± 0.5, 3.1 ± 0.1, and 3.8 ± 0.2 log PFU/g were observed for 30, 50, 70, and 100% microwave power levels when three berries were heated for 60 s. D-values were 21.4 ± 1.95 s and 10.6 ± 1.1 s at 10 and 60°C, respectively. This work demonstrates an approach to estimate inactivation parameters for viruses from dynamic temperature data during microwave heating. These findings will be useful in predicting the safety effect of microwave heating of berries in the home or food service.

Prevalence and Antibiotic Resistance of Salmonella and Campylobacter Isolates from Raw Chicken Breasts in Retail Markets in the United States and Comparison to Data from the Plant Level.

Chicken is the most popular meat in the United States, and consumers may be exposed to multidrug resistant Salmonella and Campylobacter through consumption of retail chicken breasts. This study aimed to (i) determine the percentage of raw, packaged, retail chicken breasts from 27 metro areas that tested positive for Salmonella and Campylobacter; (ii) investigate the antibiotic susceptibility profiles of a subset of the isolates; and (iii) compare the Salmonella prevalence data to establishment level Salmonella categorization data published by the U.S. Department of Agriculture (USDA). USDA Food Safety and Inspection Service (FSIS) Microbiology Laboratory Guidebook (MLG) methodology was used to isolate and identify Salmonella (n = 672), Campylobacter (n = 499) from 400 g samples. National Antimicrobial Resistance Monitoring System (NARMS) methodology was followed for antimicrobial susceptibility testing of Salmonella (n = 52) and Campylobacter (n = 16) isolates. Salmonella was found in 8.6% of samples and Campylobacter in 4.2%. Having a 3 rating in USDA's Salmonella Categorization of Individual Establishments for chicken parts was predictive of having a higher Salmonella percent positive in our data set (p ≤ 0.05). A total of 73.1% of Salmonella isolates, and 62.5% of Campylobacter isolates were resistant to ≥one class of antibiotics, with 48.1% of Salmonella isolates resistant to ≥three classes. Current results support interventions that take a 'farm-to-fork' approach with distinction by poultry types and parts as well as serovars, to lower antibiotic resistant Salmonella infections in humans due to poultry. Highlights:Salmonella was found in 8.6% and Campylobacter in 4.2% of chicken breasts tested; A 3 rating by USDA was predictive of a higher Salmonella percent positive; 48.1% of Salmonella isolates were resistant to 3 or more classes of antibiotics.

Occurrence of Listeria monocytogenes in Counter-Sliced Turkey Meat Samples from Independent Delis in New York City.

ABSTRACT: Research suggests that small, independent delicatessens are less likely to follow proper sanitation procedures, including slicer inspection, which could lead to a higher likelihood of these delis being a reservoir for Listeria monocytogenes growth and cross-contamination. This study was undertaken to determine the incidence of L. monocytogenes in counter-sliced turkey deli meat obtained from independent delis in an urban city. Deli meat, counter-sliced on site, was collected from 118 independent delis in New York City. The samples were analyzed for L. monocytogenes using the U.S. Department of Agriculture Microbiology Laboratory Guidebook methodology for isolation and confirmation. The selection criteria for delis included using the city's restaurant inspection and grading system. Two samples, from separate delis, were confirmed as positive for L. monocytogenes (1.69%). Analysis of the genomic sequences of one of the samples revealed a close match to a cluster of six clinical isolates, which were part of an ongoing multistate listeriosis outbreak spanning four states. The sequence of the second isolate matched a clinical isolate in a neighboring state. Both isolates were obtained from delis that did not have the top inspection grade. Although a snapshot of one urban area, this study is the first report on the current incidence of L. monocytogenes on counter-sliced deli meat from independent deli establishments. This study suggests that these delis can potentially serve as sources of L. monocytogenes contamination or contribute to downstream foodborne listeriosis. Information provided by city inspection and grading systems, in addition to the letter grade, may serve as a tool to identify delis with potential L. monocytogenes contamination issues and a basis for product and environmental sampling by public health authorities.

Longer Contact Times Increase Cross-Contamination of Enterobacter aerogenes from Surfaces to Food.

Bacterial cross-contamination from surfaces to food can contribute to foodborne disease. The cross-contamination rate of Enterobacter aerogenes on household surfaces was evaluated by using scenarios that differed by surface type, food type, contact time (<1, 5, 30, and 300 s), and inoculum matrix (tryptic soy broth or peptone buffer). The surfaces used were stainless steel, tile, wood, and carpet. The food types were watermelon, bread, bread with butter, and gummy candy. Surfaces (25 cm2) were spot inoculated with 1 ml of inoculum and allowed to dry for 5 h, yielding an approximate concentration of 107 CFU/surface. Foods (with a 16-cm2 contact area) were dropped onto the surfaces from a height of 12.5 cm and left to rest as appropriate. Posttransfer, surfaces and foods were placed in sterile filter bags and homogenized or massaged, diluted, and plated on tryptic soy agar. The transfer rate was quantified as the log percent transfer from the surface to the food. Contact time, food, and surface type all had highly significant effects (P < 0.000001) on the log percent transfer of bacteria. The inoculum matrix (tryptic soy broth or peptone buffer) also had a significant effect on transfer (P = 0.013), and most interaction terms were significant. More bacteria transferred to watermelon (∼0.2 to 97%) than to any other food, while the least bacteria transferred to gummy candy (∼0.1 to 62%). Transfer of bacteria to bread (∼0.02 to 94%) was similar to transfer of bacteria to bread with butter (∼0.02 to 82%), and these transfer rates under a given set of conditions were more variable than with watermelon and gummy candy. IMPORTANCE: The popular notion of the "five-second rule" is that food dropped on the floor and left there for <5 s is "safe" because bacteria need time to transfer. The rule has been explored by a single study in the published literature and on at least two television shows. Results from two academic laboratories have been shared through press releases but remain unpublished. We explored this topic by using four different surfaces (stainless steel, ceramic tile, wood, and carpet), four different foods (watermelon, bread, bread with butter, and gummy candy), four different contact times (<1, 5, 30, and 300 s), and two bacterial preparation methods. Although we found that longer contact times result in more transfer, we also found that other factors, including the nature of the food and the surface, are of equal or greater importance. Some transfer takes place "instantaneously," at times of <1 s, disproving the five-second rule.