Potential use of presumptive enterococci and staphylococci as indicators of sanitary condition in plants making hard Italian-type cheese

Raw milk, pasteurized milk, unripened cheese (1 day old), and partially rip ened cheese (3 months) from 42 milk lots at a plant making hard Italian-typ e cheese were analyzed for presumptive enterococci using kanamycin esculin azide agar pour plates. Fully ripened (greater than or equal to 10 months) cheeses, derived from other milk lots, were also tested. Numbers of presump tive staphylococci (Baird-Parker agar [B-P]) were determined in the partial ly and fully ripened cheeses. Presumptive enterococci were ubiquitous in ra w milk, usually at levels of 2.1 to 3.0 log CFU/ml. Enterococci were detect ed in 11 (26%) of 42 pasteurized milk samples. Enterococci and staphylococc i were detected in 39 (93%) and 6 (14%) of unripened cheeses and in 33 (80% ) and 4 (10%) of partially ripened cheeses, respectively. Only eight and fi ve samples of enterococci-positive unripened and partially ripened cheese, respectively, were made from pasteurized milk in which presumptive enteroco cci were detected. Of 42 samples of fully ripened cheese, 35 (83%) and 8 (1 9%), respectively, contained presumptive enterococci and staphylococci. Res ults suggest either that low numbers of presumptive enterococci survive pas teurization and cheese ripening or that contamination of cheese by enteroco cci occurs after pasteurization. Biochemical testing confirmed 63% of presu mptive enterococci isolates. None of the 20 presumptive staphylococci isola tes produced colonies typical of Staphylococcus aureus on B-P agar; the iso lates were identified as 1 Staphylococcus epidermidis, 1 Staphylococcus xyl osus, 2 Staphylococcus saprophyticus, 1 Staphylococcus warneri, 5 Kocuria s pp., and 10 unidentified gram-positive, catalase-positive cocci. Three stap hylococci isolates decreased in numbers by more than 3.0 log CFU/ml in 9.9 ml of skim milk heated 30 min in a 62.8 degreesC water bath. This finding s uggests that most presumptive staphylococci detected may have been prepaste urization contaminants. Unless specificity of the kanamycin esculin azide a nd B-P media is improved, use of presumptive enterococci and staphylococci as indicators of postpasteurization sanitation in plants making hard Italia n-type cheese cannot be recommended.