Behavior of Salmonellae During Manufacture and Ripening of Manchego Cheese

Six Salmonella strains were inoculated into 12 vats (2 vats/strain) of pasteurized sheep milk at a level of 10⁴ cells/ml, and Manchego cheese was manufactured by usual procedures, with 1% of a Streptococcus lactis culture as starter. Growth of Salmonella occurred during the first 6-9 h, with mean increases in log counts of 1.67, 1.49 and 1.71 respectively for Salmonella enteritidis , S. typhi and S. typhimurium ; data inversely correlated to pH decrease. Mean numbers of Salmonella declined during the first week by 4.43, 1.18 and 3.97 log cycles for the three serotypes, respectively, with a significant correlation between decreases in pH and in Salmonella log counts. Salmonella survived for 4 weeks in 9 vats, for 6 weeks in 3 vats and was absent from all lots of 8-week Manchego cheese. Brilliant green agar yielded the highest productivity among five selective agars used for the enumeration of Salmonella by direct-plating procedures, while enrichment in selenite cystine broth followed by streaking to bismuth sulfite agar gave the highest Salmonella recovery of all eight broth-agar combinations tested.