OCCURRENCE OF INHIBITORY COMPOUNDS IN SPENT GROWTH MEDIA THAT INTERFERE WITH ACID-TOLERANCE OF ENTERIC PATHOGENS

Authors: YINGRU, CHEN - NGEE A POLYT, SINGAPORE; LIMING, SAMANTHA - NGEE A POLYT,SINGAPORE; Bhagwat, Arvind

Submitted to: International Journal of Food Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/16/2003
Publication Date: 1/1/2004
Citation: Yingru, C., Liming, S.H., Bhagwat, A.A. 2004. Occurrence of inhibitory compounds in spent growth media that interfere with acid-tolerance of enteric pathogens. International Journal of Food Microbiology. 91:175-183.

Interpretive Summary: Food safety has become a major and increasing concern in recent years. We are studying the problem of microbial safety of fresh fruits and vegetables, which are often acidic. The ability of human pathogens to survive in an acidic environment is critical in their ability to cause disease. Acidic produce, such as apple cider and juice, as well as fresh-cut (pre-cut, pre-packaged) melons and tomatoes have been implicated in recent outbreaks of infections caused by E. coli O157:H7. Survival of pathogens such as E. coli O157:H7 for extended periods of time on fresh-cut produce is a serious cause of concern. In this study, we found that some compounds remaining in the media after growing these bacteria under laboratory conditions decrease the acid tolerance of E. coli O157:H7, Salmonella and Vibrio, three important foodborne human pathogens. Therefore, these compounds may be useful as a treatment for limiting growth of human pathogens on fresh produce. The compounds retain their function after treatment at high temperatures. Thus, in addition to offering ways to limit growth of human pathogens on fresh produce, they may also offer novel ways to improve microbial food safety of processed foods, which often receive a form of heat treatment. Understanding acid tolerance of human pathogens will benefit the food industry, as well as increase the microbial food safety of the food supply of all Americans.

Technical Abstract: Understanding the acid-tolerance ability of enteric human pathogens is critical in determining microbial food safety and the associated risk. We have discovered naturally occurring compounds in the spent growth media, which inhibit the acid tolerance ability of several enteric human pathogens when challenged at pH 3.0 for 2 h at 37°C. The compounds were detected in the spent growth media obtained from Escherichia coli O157:H7, Salmonella spp., and Vibrio cholera, but not from Shigella flexneri. The compounds were effective in reducing pathogen survival by 5-logs during acid challenge assay. The low molecular weight (< 300 Dalton) and heat resistant nature (121°C, 15 min, at 15 psi) of the compounds make them excellent candidates to explore their suitability as food additives that would increase microbial food safety.