Survival and growth of Escherichia coli O157:H7 in roast beef and salami after exposure to an alkaline cleaner

Survival and growth of wild-type (EDL 933) and rpoS-deficient (FRIK 816-3) strains of Escherichia coli O157:H7 after exposure to an alkaline cleaner for 2 min and inoculating into roast beef (pH 6.3) and hard salami (pH 4.9) at low (0.003 to 0.52 CFU/g) and high (0.69 to 31.5 CFU/g) populations were determined. Roast beef was stored at 4 and 12 degrees C; salami was stored at 4, 12, and 20 degrees C. At 4 degrees C, untreated cells of both strains showed greater reductions in populations in salami than in roast beef during a 21-day storage period. Populations of treated and untreated cells recovered from roast beef and salami stored at 4 degrees C on tryptic soy agar were significantly (P < or = 0.05) higher than on sorbitol MacConkey agar, indicating that a portion of the cells was injured. Treated and untreated cells grew in roast beef at 12 degrees C. Growth of treated cells of the FRIK 816-3 strain in roast beef at 12 degrees C was significantly slower than that of the EDL 933 strain. Populations of both strains decreased at different rates in salami stored at different temperatures (20 degrees C > 12 degrees C > 4 degrees C). E. coli O157:H7 strain EDL 933 grew more rapidly at 20 degrees C in a slurry (pH 5.97) prepared from stored salami (17 days at 20 degrees C) on which Penicillium chrysogenum had grown than in a slurry (5.23) prepared from salami showing no mold growth. Within 2 to 3 days, populations were ca. 3 log CFU/ml higher in slurry made from infected salami than in control salami. Results indicate that treatment of E. coli O157: H7 with an alkaline cleaner for 2 min does not impair resuscitation and growth of surviving cells in roast beef at 12 degrees C. Cross protection of cells exposed to an alkaline cleaner against subsequent stress conditions imposed by roast beef and salami stored at 4 degrees C was not evident in either of the test strains.