Influence of lactic acid bacteria on survival of Escherichia coli O157 : H7 in inoculated minas cheese during storage at 8.5 degrees C

Minas cheese is a typical Brazilian fresh cheese, manufactured by addition of rennin and CaCl2 to milk, followed by draining the curd. The intrinsic c haracteristics of this product make it favorable for growth of pathogens, i ncluding Escherichia coli O157:H7. The influence of the addition of a comme rcial mesophilic type O lactic culture to this product on the growth of thi s pathogen during storage at 8.5 degreesC was evaluated. Eight different fo rmulations of Minas cheese were manufactured using raw or pasteurized milk and with or without salt and lactic culture. Individual portions of each fo rmulation were transferred to sterile plastic bags and inoculated with E. c oli O157:H7 to yield ca. 10(3) or 10(6) CFU/g. After blending by hand massa ging the bags, samples were stored at 8.5 degreesC for up to 14 days. E. co li O157:H7 was counted after 1, 2, 7, and 14 days of storage using 3M Petri film Test Kit-HEC. Counts in samples without added lactic culture showed a 2-log increase in the first 24 h and remained constant during the following 14 days. Counts in samples with added lactic culture showed a 0.5-log incr ease in the first 24 h, followed by a decrease. These variations were stati stically significant (P < 0.05). No significant variations (P > 0.05) were obtained for cheese samples manufactured with pasteurized or raw milk, with or without salt. Results indicate that the addition of type O lactic cultu re may be an additional safeguard to well-established good manufacturing pr actices and hazard analysis and critical control point programs in the cont rol of growth of E. coli O157:H7 in Minas cheese.