Survival of Salmonella typhimurium and Escherichia coli O157 : H7 in cheese brines

Survival of Salmonella typhimurium and Escherichia coli O157:H7 was studied in model brines and brine from three cheese plants. Three strain mixtures of S. typhimurium and E. coli O157:H7 (10(6) CFU/ml) were inoculated separa tely into 23% model brine with or without added pasteurized whey (2%) and a s a combined inoculum into the commercial brines. The model brines were inc ubated at 8 and 15 degrees C for 28 days, and the commercial brines at 4 an d 13 degrees C for 35 days. Populations of both pathogens in the model brin e + whey decreased slowly over 28 days (1.0-2.0 log CFU/ml) with greater su rvival at 8 degrees C than at 15 degrees C. Corresponding decreases in mode l brine without whey were 1.9-3.0 log CFU/ml, with greater survival at 8 de grees C than at 15 degrees C. Both S. typhimurium and E. coli O157:H7 survi ved significantly better (P < 0.05) at 4 degrees C than at 13 degrees C in two of the commercial brines. The survival of each pathogen in the commerci al brines at 13 degrees C was significantly influenced by brine pH. Both pa thogen populations decreased most rapidly in commercial brines during the f irst week of storage (2.5-4.0 and 2.3-2.8 log CFU/ml for S. typhimurium and E. coli O157:H7, respectively) with significant recovery (ca. 0.5 log CFU/ ml increase) often occurring in the second week of storage. Counts changed little thereafter. Overall, E. coli O157:H7 survived better than S. typhimu rium, with differences of 0.1-1.2 log CFU/ml between the two pathogens. Res ults of this study show that cheese brine could support the survival of con taminating S. typhimurium and E. coli O157:H7 for several weeks under typic al brining conditions. (C) 2000 Elsevier Science B.V. All rights reserved.