Pathogen-produce pair attribution risk ranking tool to prioritize fresh produce commodity and pathogen combinations for further evaluation (P3ARRT)

Foodborne disease outbreaks and cases associated with fresh produce have increased over the past decade. In developing approaches to prevent or reduce illnesses from consumption of contaminated produce, new tools are needed to identify and prioritize appropriate efforts. The purpose of this study was to develop a semi-quantitative risk ranking tool (Pathogen-Produce Pair Attribution Risk Ranking Tool, or P³ARRT) to rank the relative public health impact of pathogen-produce commodity combinations, based on explicit data-driven criteria. To identify candidate pathogen-commodity pairs, a database was created that included all published reports of fresh produce-associated outbreaks in the United States. A total risk score was calculated for each pathogen-commodity pair as the summation of nine criteria scores multiplied by the respective criteria weighting. A total of 53 pathogen-produce commodity pairs were included in the risk ranking, and based on scenario and sensitivity analyses, enterohemorrhagic E. coli in leafy greens consistently ranked first, followed by Salmonella spp. in tomatoes, and Salmonella spp. in leafy greens. The P³ARRT model provides a systematic, transparent, and customizable tool with which to prioritize produce pathogen-commodity pairs for further, more rigorous risk assessment modeling and evaluation efforts. The tool is available to the public at www.FoodRisk.org.     

Effect of food matrix and cell growth on PCR-based detection of Escherichia coli O157:H7 in ground beef

The purpose of this work was (i) to investigate the feasibility of a previously reported upstream processing method for PCR template preparation to facilitate the detection of Escherichia coli O157:H7 from ground beef and (ii) to assess the impact of cell growth (no growth in the matrix versus growth in the matrix) on molecular detection limits. Two food matrices (autoclaved and raw ground beef) were evaluated in all studies. For no-growth experiments, 10-g meat samples were inoculated with 10(2) to 10(7) CFU/g E. coli O157:H7 and then homogenized. The homogenates were processed to remove large particulates and inhibitors using a two-phase upstream processing method consisting of two sequential centrifugation steps, the second of which used titanous hydroxide to facilitate bacterial immobilization. After upstream processing, sample concentrates were extracted for DNA isolation and amplified by PCR. For growth experiments, 10-g meat samples were inoculated at 1 CFU of E. coli O157:H7 per gram, allowed to grow to 10(2) to 10(7) CFU/g, and then processed for PCR assay. Cell recoveries after upstream processing ranged from 15.9 to 77.6% and were not facilitated by the use of titanous hydroxide, as compared with a saline control (P > 0.05). Bacterial cell recovery and PCR detection limits were similar when comparing autoclaved ground beef and raw ground beef, but cell recoveries were highly variable for raw ground beef samples in which E. coli O157:H7 cells were allowed to grow before processing for detection. Overall, PCR detection limits approximated 10(3) CFU/g of ground beef for all treatments. These results indicate that use of model food systems may not always provide an accurate replication of real-world conditions when evaluating PCR detection limits.     

Application of classification and regression trees for sensitivity analysis of the Escherichia coli O157:H7 food safety process risk model

Microbial food safety process risk models are simplifications of the real world that help risk managers in their efforts to mitigate food safety risks. An important tool in these risk assessment endeavors is sensitivity analysis, a systematic method used to quantify the effect of changes in input variables on model outputs. In this study, a novel sensitivity analysis method called classification and regression trees was applied to safety risk assessment with the use of portions of the Slaughter Module and Preparation Module of the E. coli O157:H7 microbial food safety process risk as an example. Specifically, the classification and regression trees sensitivity analysis method was evaluated on the basis of its ability to address typical characteristics of microbial food safety process risk models such as nonlinearities, interaction, thresholds, and categorical inputs. Moreover, this method was evaluated with respect to identification of high exposure scenarios and corresponding key inputs and critical limits. The results from the classification and regression trees analysis applied to the Slaughter Module confirmed that the process of chilling carcasses is a critical control point. The method identified a cutoff value of a 2.2-log increase in the number of organisms during chilling as a critical value above which high levels of contamination would be expected. When classification and regression trees analysis was applied to the cooking effects part of the Preparation Module, cooking temperature was found to be the most sensitive input, with precooking treatment (i.e., raw product storage conditions) ranked second in importance. This case study demonstrates the capabilities of classification and regression trees analysis as an alternative to other statistically based sensitivity analysis methods, and one that can readily address specific characteristics that are common in microbial food safety process risk models.     

Heat Pipe‐Cooled Microstructured Reactor Concept for Highly Exothermal Ionic Liquid Syntheses

Heat pipes used for cooling of microstructured reactors are a new approach for sustainable processing also in the lab‐scale within a temperature range from ambient to more than 180 °C. The main advantage of heat pipe cooling is the dynamic behavior, i.e., the cooling rate depends on the heat released. Heat pipes can also suppress thermal runaways due to their extremely short response times on momentary temperature rises. As an example, the highly exothermal synthesis of 1‐ethyl‐3‐methylimidazolium trifluoromethanesulfonate from the respective reactants 1‐ethyl‐imidazole and methyltrifluoromethanesulfonate was investigated. By transferring the protocol to continuous‐flow conditions in the microscale and by applying cooling with heat pipes, an out‐of‐control processing can be avoided.     

A field study of the microbiological quality of fresh produce of domestic and Mexican origin

Produce is responsible for an increasingly larger proportion of foodborne disease outbreaks. In particular, the globalization of the food supply may introduce new food safety risks and allow widespread distribution of contaminated food, particularly produce. The objectives of this study were to: (i) compare the overall quality of domestic and Mexican produce throughout the packing process; (ii) examine changes in microbiological quality of both domestic and Mexican produce at each stage of production and processing; and (iii) evaluate the prevalence of select pathogens on fresh produce, including leafy green, herbs, melons, and vegetables. Furthermore, we also sought to characterize the antibiotic resistance profiles of Enterococcus faecium and Enterococcus faecalis strains isolated from fresh produce. A total of 466 produce and matching environmental swab samples was collected from various locations in packing sheds in the southern US from November 2002 through December 2003. These samples were assayed by enumerative tests for total aerobic bacteria (APC), total coliforms, total Enterococcus, and E. coli. Produce samples were also analyzed for the presence of Salmonella, Listeria monocytogenes, Shigella, and E. coli O157:H7. A total of 112 E. faecium and E. faecalis isolates were further screened for antibiotic resistance using a panel of seventeen antibiotics. Overall, the microbiological quality of fresh produce ranged from 4.0 to 7.9 log(10) CFU/g (APC); less than 1.0 log(10) to 4.5 log(10) CFU/g (coliforms); less than 1.0 log(10) to 4.0 log(10) CFU/g (E. coli); and less than 1.0 log(10) to 5.4 log(10) CFU/g (Enterococcus). No Salmonella, Shigella, or E. coli O157:H7 were detected from the 466 25-g produce samples tested. However, three domestic cabbage samples were found to be positive for L. monocytogenes. Of the Enterococcus isolates, E. faecium had a higher degree of resistance to antibiotics in general, while Enterococcus spp. isolated from Mexican produce had a higher degree of antibiotic resistance when compared to strains isolated from produce samples of domestic origin. Despite increased attention to the role of imported produce in foodborne disease, this study does not support the assumption that domestic produce is of higher microbial quality than Mexican produce.     

Detection and identification of histamine-producing bacteria associated with harvesting and processing mahimahi and yellowfin tuna

Histamine poisoning is one of the most common chemically induced seafoodborne illnesses reported in the United States today. The causative agents are biogenic amines, commonly produced by gram-negative bacteria. The purpose of this study was to detect and identify histamine-producing bacteria associated with standard industry practices during the harvesting, receiving, and processing of mahimahi and yellowfin tuna in North Carolina. Twenty-nine composite samples were obtained from 18 mahimahi and 11 yellowfin tuna and analyzed for their histamine content. No sample analyzed exceeded 2 ppm histamine, the lower detection limit. Composite fish muscle and environmental samples were screened (n = 386) for the presence of histamine-producing bacteria. Twenty-six percent (145) of 549 isolates selected on the basis of their morphological characteristics tested positive on Niven's media. Sixty-three Niven-positive isolates were gram negative, and 58 were gram positive. Of the 43 isolates tested further, 5 were confirmed as histamine producers, and all 5 produced at low levels (< 250 ppm in 48 h at > 15 degrees C). Three gram-negative and two gram-positive isolates were identified as Enterobacter cloacae and Staphylococcus kloosii, respectively. This study revealed that gram-negative bacteria might not be solely responsible for histamine production in at-risk fish. The confirmation of histamine-producing bacteria demonstrates the potential risk for histamine production. However, no detectable levels were found in the composite fish muscle samples analyzed even though 60% of the yellowfin tuna harvested did not meet the U.S. Food and Drug Administration's regulatory hazard analysis critical control point guidelines for temperature reduction. Therefore, no seafood safety risks were found under the standard industry practices observed in this study.     

Magnetized carbonyl iron and insoluble zirconium hydroxide mixture facilitates bacterial concentration and separation from nonfat dry milk

A mixture of magnetized carbonyl iron and insoluble zirconium hydroxide was investigated for its ability to concentrate various foodborne pathogens from 25-ml samples of reconstituted nonfat dry milk. Each sample was artificially contaminated with 10(3) to 10(6) CFU/25 ml of representative foodborne pathogens (Salmonella enterica serovar Enteritidis, Listeria monocytogenes, and Bacillus cereus spores) and processed for bacterial concentration with high-speed centrifugation for the primary concentration followed by a secondary concentration step involving the carbonyl iron-zirconium hydroxide mixture. Bacterial recoveries, as evaluated on the basis of loss to discarded supernatants, exceeded 75% for all organisms at all inoculum levels and were usually >90%. Recovery was confirmed by direct plating of the immobilized pellet, for which the valueswere similar albeit more varied. Additional experiments confirmed that the magnetized carbonyl iron-insoluble zirconium hydroxide mixture was relatively nontoxic to both Salmonella Enteritidis and L monocytogenes Overall, the entire concentration scheme resulted in a 25-fold reduction in sample volume with the recovery of viable bacterial cells. This novel compound shows promise for facilitating inexpensive, rapid, and effective bacterial concentration in food systems.     

Sensitivity analysis of Salmonella enteritidis levels in contaminated shell eggs using a biphasic growth model

Salmonella enteritidis (SE) is a common foodbome pathogen, the transmission of which is primarily associated with the consumption of contaminated Grade A shell eggs. In order to estimate the level of SE present in raw shell eggs, it is necessary to consider the protective effects of the egg albumin, which effectively inhibits SE growth in a time- and temperature-dependent manner. In this study, a SE growth model was produced by combining two mathematical equations that described both the extended lag phase of SE growth (food component) and a SE growth model (pathogen component). This biphasic growth model was then applied to various egg handling scenarios based on the farm-to-table continuum, including in-line and off-line processing facilities with consideration of key events in production, processing, transportation, and storage. Seasonal effects were also studied. Monte Carlo simulation was used to characterize variability in temperature and time parameter values influencing the level of SE to which individuals are exposed. The total level of SE consumed was estimated under best, most likely, and time-temperature abusive handling scenarios. The model estimated that, in most cases, there was no SE growth in contaminated eggs handled under most likely practices, because 10-70% of the yolk membrane remained intact. Under abusive handling scenarios, complete loss of yolk membrane integrity frequently occurred by the time eggs reach the distribution phase, followed by subsequent SE growth, which was often quite rapid. In general, the effect of season and processing method (in-line vs. off-line) was minimal. Further sensitivity analysis demonstrated that the initial SE contamination level significantly influenced the final exposure levels only under no-abuse or mildly abusive conditions. The results of our study suggest that, for maximum reduction of SE exposure level, cooling strategies should not only focus on the on-farm or processing phases, but should emphasize the importance of cooling strategies at the distribution and consumer phases of the farm-to-fork continuum.     

Changes in hair arsenic levels in breast and bottle fed infants during the first year of infancy

Hair samples were collected from 13 breast fed and 19 bottle fed infants at one, three, six and twelve months of age. Food frequency data were also collected. Arsenic and antimony concentrations determined in washed hair samples by neutron activation procedures, rose significantly with age, the highest levels being evident at twelve months. Hair arsenic and antimony levels were independent of sex, and method of milk feeding. However, at twelve months, the median hair arsenic level for those infants receiving cereal at six months of age (0.655 μg/g) was significantly higher (p = 0.05) than for those infants fed exclusively a milk based diet at this time (median = 0.225 μg/g). Recent data show that cereals are major dietary sources of arsenic during infancy. Hence findings of this study suggest that changes in hair arsenic levels during infancy are related to the introduction of cereals in the diet.