61C-10 |
Bacterial pathogen surrogate evaluation: Tolerance of cadidates to low pH and reduced water activity |
A. PERI1, S. E. Keller2, S. Ravishankar1, C. Rodríguez1, and P. J. Slade1. (1) Food Safety/ HACCP, Illinois Institute of Technology/ NCFST, 6502, S. Archer Road, Summit- Argo, IL 60501, (2) Food Safety/ HACCP, FDA/ NCFST, 6502, S. Archer Road, Summit- Argo, IL 60501 Non-pathogens are preferred in lieu of pathogenic microorganisms to evaluate the efficacy of intervention strategies in food processing operations because of the potential risk presented to both the production environment and the researchers. The objective was to conduct a systematic and comprehensive evaluation of the behavior of a number of bacteria for use as surrogates in place of various pathogens to determine the influence of specific food processing parameters, e.g., acid/alkaline pH and low aw. Escherichia coli K12 MC4100, E. coli K12 LM1010 and Listeria innocua 137 were the potential surrogates tested. Cocktails of various pathogens (Escherichia coli 0157:H7, Listeria monocytogenes, Salmonella Typhimurium, Salmonella Enteritidis) were used for comparison. Tryptic soy broth without dextrose (TSB w D) was the suspending medium. The survival of all test organisms (grown in TSB w D; initial level 106 CFU/ml) was evaluated at pH 3.0, 3.5, 4.0, 9.5 and 10.0 and at aw levels of 0.96 to 0.84. The acidulant was HCl. Glycerol & NaCl were used as the humectants. Enumeration was done on tryptic soy agar with yeast extract as the non-selective medium and on appropriate selective media. Our results showed no reduction in the surviving population of any organism at pH 4.0, 9.0 and 9.5, and aw values down to 0.92. The surviving population of E. coli K12 LM1010 did not decline below initial level at pH 3.0 and aw of 0.84. E. coli K12 LM1010, E. coli K12 MC4100 and L. innocua 137 appear to be suitable surrogates for E. coli 0157:H7, Salmonella and L. monocytogenes respectively for acid/alkaline pH and low aw stresses. As evidenced by similar counts of the bacteria on selective & non-selective media, there were no injured cells. These results will aid in the choice of suitable surrogates for food- borne pathogens in food processing operations.
Session 61C, Food Microbiology: General I
|