How Many Bacteria Do You Bring Home with Your Veggies? John Lopes Microcide, Inc. 2209 Niagara Drive Troy, MI 48083-5933 248/526-9663 Paper P-107, Session 257-P Prewashed and packaged vegetables purchased from a local supermarket showed a heavy load of bacteria. Interestingly, bacterial population on samples of a vegetable with aerial growth such as cauliflower was lower than that on a vegetable of subsoil origin such as radish. Cauliflower showed average population density of 63 thousand bacteria per gram and radish showed average population density of 16 million bacteria per gram. This converts to about 6.3 million and about 1.6 billion bacteria per 100 grams (3.5 oz) serving of cauliflower and radish, respectively. In addition, radish also showed the presence of Listeria and Aeromonas species with potential to cause foodborne illnesses. Antibiotic-resistant Listeria and Salmonella bacteria were used to study growth of foodborne pathogens on vegetables. Millions of antibiotic-resistant Listeria and Salmonella bacteria attached to these vegetables within 15 minutes of contact with the respective cell suspension. This showed that even!
a brief period of contact with polluted water, if used for washing vegetables, can contaminate the produce. Vegetables grown in soil with animal manure are likely to carry a heavy load of pathogens. Storage of vegetables at refrigeration temperature slowed the growth of bacteria originally present and even suppressed the growth of antibiotic-resistant Listeria and Salmonella attached to the vegetables from cell suspension. The growth of both bacteria originally present and the antibiotic-resistant pathogens on vegetables, stored at 41∞ F, 50∞ F and 75∞ F for 48 hours, was investigated. The original bacterial population increased at all storage temperatures on cauliflower and radish. However, the increase was slower at lower temperature than higher temperature. Bacterial growth on cauliflower was about 13 times less at 41∞ F than at 75∞ F. Radish, which already had a much higher starting bacterial population, the increase was less conspicuous. The vegetables contaminated with antibiotic-resistant Listeria and Salmonella showed a decrease in the initial bacterial population after storage at 41∞ F. However, the population increased at the storage temperature rose. Thus, to r! educe the risk of foodborne illness, the vegetables should always be stored at proper refrigeration temperatures of 39∞ F to 41∞ F. This investigation was carried out by Dr. John Lopes, Mr. Andy Rillo and Ms. Rose Lopes at the Research Laboratories of Microcide, Inc., Detroit, Michigan. The work was funded by a SBIR Phase I grant from the National Institutes of Health, Infectious Disease Branch, to develop safe and nontoxic sanitizers for fresh fruits and vegetables. The investigation was presented at the 98th General Meeting of the American Society for Microbiology in Atlanta, Georgia, on May 21, 1998. The evidence is based on enumerating and identifying bacteria on cauliflower and radish purchased from a supermarket. The evidence shows the extent of the contamination of produce and potential risk associated with contaminated vegetables. The contamination of vegetables can come from various sources: Polluted soil and irrigation water, contaminated water and equipment in the processing plant, filthy transport vehicles and containers and unhygienic food plant workers can contribute to contamination of vegetables by the foodborne pathogens. Once contaminated the bacterial population can increase during storage at temperatures higher than the refrigeration temperature (41∞ F). Even vegetables purchased from a supermarket should be stored refrigerated at home and washed prior to consumption. There were several instances of foodborne outbreaks of infections due to contaminated fruits and vegetables. Contaminated cantaloupes accounted for 645 cases during 1990 and 1991, contaminated tomatoes for 258 cases during 1990 and 1993, and contaminated alfalfa sprouts for 242 cases during 1995 of foodborne illnesses due to Salmonella infections. Contaminated leafy lettuce accounted for 119 cases of foodborne illnesses due to E. coli O157:H7. It should be noted that these are only the reported cases to the public health departments. The magnitude of foodborne illnesses is often underestimated because of numerous isolated cases remain undiagnosed and/or are not reported.
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