61C-27

J. Campbell, J. H. ISONHOOD, and M. A. Drake. Dept. Food Science, North Carolina State University, Raleigh, NC 27695

Enterohemorrhagic E. coli (EHEC) are foodborne pathogens which can cause a spectrum of illness ranging from diarrhea to hemolytic uremic syndrome (HUS). Studies with EHEC and other pathogens have shown that sublethal stress encountered in storage and processing can impact subsequent stress tolerance. EHEC have at least two acid resistance mechanisms, one of which is regulated by glutamate.

The objectives of this study were to determine the impact of salt and monosodium glutamate on cold and cold/acid survival and subsequent acid tolerance and to determine the impact of monosodium glutamate (MSG) on growth in acidic conditions.

Cold storage survival was conducted in tryptic soy broth (TSB) as a split plot design (main plot=pH 7.0, 5.0, or 4.0, subplot=MSG x salt). A three strain cocktail of E. coli O157:H7 was used as inoculum. Survival was monitored weekly through 21 d at 5C. Acid tolerance in simulated gastric fluid was evaluated weekly. In separate experiments, four strains were tested individually for the effect of growth in the presence of MSG on subsequent acid resistance and for the ability of MSG to impact growth under acid conditions.

Salt and MSG impacted cold storage survival (p<0.05). Cold storage survival decreased with increasing salt (0, 2, 4%) and increased with MSG (0, 0.5, 1%). The impact of salt or MSG was greater at pH 4.0 than at pH 5.0 or 7.0. MSG or salt did not enhance acid tolerance following cold storage (p>0.05). Overnight growth in TSB containing MSG had no impact on subsequent acid tolerance in acidified TSB (pH 2.0) without MSG (p>0.05). The presence of MSG in acidified TSB (37C) enhanced survival and growth at lower pH than TSB without MSG.

The presence of MSG can impact survival and minimum growth pH of E. coli O157:H7.

Session 61C, Food Microbiology: General I
2:00 PM - 5:30 PM, 2002-06-17

2002 Annual Meeting and Food Expo - Anaheim, California