Fate of enterotoxigenic Staphylococcus aureus in the presence of nisin-producing Lactococcus lactis strain during manufacture of Jben, a Moroccan traditional fresh cheese

The inhibitory effect of nisin-producing Lactococcus lactis subsp. lactis UL730 on the growth of enterotoxigenic Staphylococcus aureus J10 during manufacture of Jben, a Moroccan traditional fresh cheese prepared from recombined milk, was investigated. With an inoculum level of 10(3) cfu mL(-1), S. aureus was absent in Jben four days after inoculation when the nisin-producing lactococcus was used as lactic starter. In contrast, it survived after that period, when the starter was non-nisin-producing. No staphylococcal thermonuclease was detected in all Jben samples made from milk inoculated with S. aureus at the level of 10(3) cfu mL(-1). With a higher inoculum of 10(5) cfu mL(-1), S. aureus was still present in Jben after manufacture and persisted during the storage of the product for 3 days in the laboratory, even when the starter used was nisin-producing. Staphylococcal thermonuclease and type C enterotoxin were detected in all Jben samples made from milk inoculated with 10(5) cfu mL(-1). Thermonuclease and enterotoxin were already produced in the coagulum, at 24 h after milk inoculation with S. aureus. (C) 2002 Elsevier Science Ltd. All rights reserved.