BIOLUMINESCENCE - A RAPID INDICATOR OF ESCHERICHIA-COLI O157-H7 IN SELECTED YOGURT AND CHEESE VARIETIES

Outbreaks of enterohemorrhagic Escherichia coli O157:H7 have been comm only associated with products derived from ground beef, but recently t he organism has been implicated as the causative agent in outbreaks in volving yogurt and cheese. This finding has raised concern about the p otential for its growth and survival in fermented dairy products. A bi oluminescent strain of E. coli O157:H7 was used to determine postproce ssing survival in yogurt with live cultures at pH 4.17, 4.39, and 4.47 stored at 4 and 10 degrees C. In addition, survival of E. coli O157:H 7 was monitored during the manufacture of Cottage, Colby, Romano, and Feta cheeses. Results indicated survival for 8 and 5 days at. 4 and 10 degrees C respectively in yogurt at pH 4.17, 17 acid 15 days at 4 and 10 degrees C respectively in yogurt at pH 4.39, and 17 days at both 4 and 10 degrees C in yogurt at pH 4.47. E. coli O157:H7 did not surviv e cooking procedures at 56 degrees C in Cottage cheese. However, the p athogen survived for 27, 30, and 27 days in Colby, Romano, and Feta ch eeses respectively. A high correlation of r(2) > 0.89 was obtained bet ween counts of bioluminescenct colonies and standard plate count for a ll yogurt and cheese varieties, indicating that bioluminescence was a sensitive and rapid indicator of cellular viability for E. coli O157:H 7. Survival of the pathogen, as indicated by this method, is possible in highly acidic environments even at refrigeration temperatures. This poses a potential hazard should postprocessing contamination occur.