Future challenges to microbial food safety

Despite significant efforts by all parties involved, there is still a considerable burden of foodborne illness, in which micro-organisms play a prominent role. Microbes can enter the food chain at different steps, are highly versatile and can adapt to the environment allowing survival, growth and production of toxic compounds. This sets them apart from chemical agents and thus their study from food toxicology. We summarize the discussions of a conference organized by the Dutch Food and Consumer Products Safety Authority and the European Food Safety Authority. The goal of the conference was to discuss new challenges to food safety that are caused by micro-organisms as well as strategies and methodologies to counter these. Management of food safety is based on generally accepted principles of Hazard Analysis Critical Control Points and of Good Manufacturing Practices. However, a more pro-active, science-based approach is required, starting with the ability to predict where problems might arise by applying the risk analysis framework. Developments that may influence food safety in the future occur on different scales (from global to molecular) and in different time frames (from decades to less than a minute). This necessitates development of new risk assessment approaches, taking the impact of different drivers of change into account. We provide an overview of drivers that may affect food safety and their potential impact on foodborne pathogens and human disease risks. We conclude that many drivers may result in increased food safety risks, requiring active governmental policy setting and anticipation by food industries whereas other drivers may decrease food safety risks. Monitoring of contamination in the food chain, combined with surveillance of human illness and epidemiological investigations of outbreaks and sporadic cases continue to be important sources of information. New approaches in human illness surveillance include the use of molecular markers for improved outbreak detection and source attribution, sero-epidemiology and disease burden estimation. Current developments in molecular techniques make it possible to rapidly assemble information on the genome of various isolates of microbial species of concern. Such information can be used to develop new tracking and tracing methods, and to investigate the behavior of micro-organisms under environmentally relevant stress conditions. These novel tools and insight need to be applied to objectives for food safety strategies, as well as to models that predict microbial behavior. In addition, the increasing complexity of the global food systems necessitates improved communication between all parties involved: scientists, risk assessors and risk managers, as well as consumer

Clostridium perfringens: spores & cells, media & modeling

Clostridium perfringensis one of the five major food borne pathogens in the western world (expressed as cases per year). Symptoms of C. perfringens food poisoning are caused by an enterotoxin, which is released when ingested cells sporulate in the intestines. To increase knowledge on this bacterium, it was tried to optimize sporulation of a variety of strains, but only strain dependent effects were noted. Since many media are available to isolate C. perfringens from foods, a selection of these media was compared and it was shown that these media performed equally well. Cooling and storage of food are often the cause of gastro enteritis. Therefore, the behavior of this microorganism was studied at low temperatures and a model was designed to predict the effect of various cooling procedures applied to food on growth of C. perfringens . The model can be used to set up Good Manufacturing Procedures (GMP)

Modeling growth of Clostridium perfringens in pea soup during cooling

Clostridium perfringens is a pathogen that mainly causes food poisoning outbreaks when large quantities of food are prepared. Therefore, a model was developed to predict the effect of different cooling procedures on the growth of this pathogen during cooling of food: Dutch pea soup. First, a growth rate model based on interpretable parameters was used to predict growth during linear cooling of pea soup. Second, a temperature model for cooling pea soup was constructed by fitting the model to experimental data published earlier. This cooling model was used to estimate the effect of various cooling environments on average cooling times, taking into account the effect of stirring and product volume. The growth model systematically overestimated growth of C. perfringens during cooling in air, but this effect was limited to less than 0.5 log N/ml and this was considered to be acceptable for practical purposes. It was demonstrated that the growth model for C. perfringens combined with the cooling model for pea soup could be used to sufficiently predict growth of C. perfringens in different volume sizes of pea soup during cooling in air as well as the effect of stirring, different cooling temperatures, and various cooling environments on the growth of C. perfringens in pea soup. Although fine-tuning may be needed to eliminate inaccuracies, it was concluded that the combined model could be a useful tool for designing good manufacturing practices (GMP) procedures

Behavior of Clostridium perfringens at low temperatures

Refrigerated storage is an important step in the preparation of foods and inadequate storage is one of the main causes of food poisoning outbreaks of Clostridium perfringens. Therefore, growth and germination characteristics of C. perfringens in a temperature range of 3-42 degreesC were determined in fluid thioglycollate broth (FTG) and Dutch pea soup. To study the effect of adaptation, cells were either inoculated from a 37 degreesC pre-culture or from a temperature-adapted pre-culture. Membrane fatty acid patterns were determined at all temperatures to examine the effect of temperature on membrane composition. Spores were either inoculated with and without heat treatment. Adaptation of cells did not influence growth rate nor lag phase. Growth in pea soup, however, was slower and lag phases tended to be more extended compared to FTG. No growth was observed at temperatures less than or equal to 10 degreesC and death rates in pea soup were higher than those in FTG at these low temperatures. Cells preserved the membrane fluidity by reducing the arachidic acid content and increasing the lauric acid content when the temperature dropped. This resulted in a net reduction in chain length. Microscopic analysis of cells grown at 15 degreesC revealed a morphological change: cells were elongated compared to those grown at 37 degreesC. These data demonstrate the ability of C. perfringens to adapt to lower temperatures. However, this did not influence growth characteristics compared to non-adapted cells. Spores of C perfringens did germinate at all temperatures with and without heat-activation. Combining this fact with the extended survival at low temperatures emphasizes the need for adequate heating of refrigerated foods before consumption to eliminate health risks due to C perfringens. (C) 2004 Elsevier B.V. All rights reserved

Optimizing sporulation of Clostridium perfringens

Many sporulation media have been developed for Clostridium perfringens, but none stimulates sporulation for all strains. The aim of our experiments was to develop a sporulation method using Duncan and Strong (DS) medium, which supports sporulation of a wide variety of strains. Different inoculation levels were tested, and the effects of sporulation-promoting substances and acid shock were evaluated. Furthermore, DS medium was compared with other sporulation media. Highest spore numbers in DS medium were obtained with a 10␂4-h fluid thioglycollate broth inoculum (5.0 x 105/ml). Addition of theophylline and replacement of starch by raffinose increased spore yields for some strains, but most strains were not affected (average increases in log N/ml of 0.2 and 0.3, respectively). One strain was enhanced by the addition of bile, but other strains were strongly inhibited (average decrease in log N/ml of 2.5); agar did not influence sporulation. Neither short-time acid exposure nor addition of culture supernatant fluids of well-sporulating strains resulted in higher spore numbers in DS medium. None of the tested methods enhanced sporulation in general; only strain-dependent effects were obtained. Peptone bile theophylline medium was the most promising sporulation medium tested; peptone bile theophylline starch medium yielded highest spore numbers (2.5 x 105/ml), but some strains failed to sporulate. In conclusion, adding theophylline to DS medium may optimize sporulation of C. perfringens, but peptone bile theophylline medium with or without starch is most suitable

Effect of cooling on Clostridium perfringens in pea soup

Foods associated with Clostridium perfringens outbreaks are usually abused after cooking. Because of their short generation times, C. perfringens spores and cells can grow out to high levels during improper cooling. Therefore, the potential of C. perfringens to multiply in Dutch pea soup during different cooling times was investigated. Tubes of preheated pea soup (50degreesC) were inoculated with cocktails of cells or heat-activated spores of this pathogen. The tubes were linearly cooled to 15degreesC in time spans of 3, 5, 7.5, and 10 h and were subsequently stored in a refrigerator at 3 or 7degreesC for up to 84 h. Cell numbers increased by 1-log cycle during the 3-h cooling period and reached their maximum after 10 It of cooling. Subsequent refrigeration hardly reduced cell numbers. Cooling of 3.75 liters of pea soup in an open pan showed that this amount of pea soup cooled from 50 to 15degreesC in 5 h, which will allow a more than 10-fold increase in cell numbers. These findings emphasize the need of good hygienic practices and quick cooling of heated foods after preparation

Cross-contamination in the kitchen: estimation of transfer rates for cutting boards, hands and knives

Aims: To quantify cross-contamination in the home from chicken to readyto-eat salad. Methods and Results: Based on laboratory scenarios performed by de Jong et al. (2008), transfer rates were estimated for Campylobacter jejuni and Lactobacillus casei as a tracer organism. This study showed that transfer characteristics for both micro-organisms were comparable when washing regimes and transfer via items (cutting board, hands and knives) were compared. Furthermore, the study showed that the use of separate transfer rates for transfer from chicken to items and from items to salad will lead to an overestimation of campylobacteriosis risk. Applying good hygienic practices resulted in final levels of bacteria in the salad below the detection limit. Our study showed that it is important to include these data points in model fitting. Conclusions: Results obtained in observational studies with Lact. casei can be translated to Camp. jejuni using the transfer rates obtained in this study. Cross-contamination by hands, cutting boards and knives was equally important. Significance and Impact of the Study: Cross-contamination should be incorporated in microbiological risk assessments. The present study contributes to this by quantifying transfer of Camp. jejuni and Lact. casei from raw chicken via various contact surfaces into the ready-to-eat produc

Cross-contamination in the kitchen: estimation of transfer rates for cutting boards, hands and knives

Aims: To quantify cross-contamination in the home from chicken to readyto-eat salad. Methods and Results: Based on laboratory scenarios performed by de Jong et al. (2008), transfer rates were estimated for Campylobacter jejuni and Lactobacillus casei as a tracer organism. This study showed that transfer characteristics for both micro-organisms were comparable when washing regimes and transfer via items (cutting board, hands and knives) were compared. Furthermore, the study showed that the use of separate transfer rates for transfer from chicken to items and from items to salad will lead to an overestimation of campylobacteriosis risk. Applying good hygienic practices resulted in final levels of bacteria in the salad below the detection limit. Our study showed that it is important to include these data points in model fitting. Conclusions: Results obtained in observational studies with Lact. casei can be translated to Camp. jejuni using the transfer rates obtained in this study. Cross-contamination by hands, cutting boards and knives was equally important. Significance and Impact of the Study: Cross-contamination should be incorporated in microbiological risk assessments. The present study contributes to this by quantifying transfer of Camp. jejuni and Lact. casei from raw chicken via various contact surfaces into the ready-to-eat produc

Cross-contamination in the kitchen: effect of hygiene measures

Aims: To determine the effect of hygiene measures on cross-contamination of Campylobacter jejuni at home and to select a safe tracer organism for C. jejuni. Methods and Results: Comparative tests were conducted with nonpathogenic Escherichia coli and Lactobacillus casei and L. casei was chosen as the safe tracer organism. Salads containing chicken breast fillet contaminated with a known number of C. jejuni and L. casei were prepared according to different cross-contamination scenarios and contamination levels of salads were determined. Cross-contamination could be strongly reduced when cleaning cutting board and cutlery with hot water (68°C), but generally was not prevented using consumer-style cleaning methods for hands and cutting board. Conclusions: Dish-washing does not sufficiently prevent cross-contamination, thus different cutting boards for raw meat and other ingredients should be used and meat¿hand contact should be avoided or hands should be thoroughly cleaned with soap. Lactobacillus casei can be used as a safe tracer organism for C. jejuni in consumer observational studies. Significance and Impact of the Study: Cross-contamination plays an important role in the transmission of food-borne illness, especially for C. jejuni. This study delivers suitable data to quantitatively assess the risk of campylobacteriosis caused by cross-contamination and it shows the effect of different preventive hygiene measures

Cross-contamination in the kitchen: effect of hygiene measures

Aims: To determine the effect of hygiene measures on cross-contamination of Campylobacter jejuni at home and to select a safe tracer organism for C. jejuni. Methods and Results: Comparative tests were conducted with nonpathogenic Escherichia coli and Lactobacillus casei and L. casei was chosen as the safe tracer organism. Salads containing chicken breast fillet contaminated with a known number of C. jejuni and L. casei were prepared according to different cross-contamination scenarios and contamination levels of salads were determined. Cross-contamination could be strongly reduced when cleaning cutting board and cutlery with hot water (68°C), but generally was not prevented using consumer-style cleaning methods for hands and cutting board. Conclusions: Dish-washing does not sufficiently prevent cross-contamination, thus different cutting boards for raw meat and other ingredients should be used and meat¿hand contact should be avoided or hands should be thoroughly cleaned with soap. Lactobacillus casei can be used as a safe tracer organism for C. jejuni in consumer observational studies. Significance and Impact of the Study: Cross-contamination plays an important role in the transmission of food-borne illness, especially for C. jejuni. This study delivers suitable data to quantitatively assess the risk of campylobacteriosis caused by cross-contamination and it shows the effect of different preventive hygiene measures