Survival and Growth of Staphylococcus aureus in Commercially Manufactured Brazilian Minas Cheese

Abstract

The potential for Staphylococcus aureus survival, growth and enterotoxigenesis in Minas cheese was studied. Twenty lots of cheese were made with raw and pasteurized milk and with and without starter culture. Cheese milk was inoculated with S. aureus strains 100, 243 or 137 and a pooled inoculum at levels of (log10) 4.23 to 6 cells/ml. Use of starter, type of inoculum, ripening time and interaction of starter by strain affected significantly the final pH of the cheese (5.22 with starter versus 5.45 without starter). Final NaCl content of cheeses differed significantly (P < 0.01) with lot indicating lack of uniformity in salting. Moisture was affected significantly by S. aureus inoculum, time of ripening and use of starter (P < 0.05). Final moisture ranged from 30.6 to 45.6%. Highly statistically significant effects on S. aureus counts during ripening were observed for use of starter (P < 0.001), type of S. aureus inoculum (P < 0.001) and time of ripening (P < 0.05). Use of starter culture had an inhibitory effect on S. aureus growth. Use of raw or pasteurized milk did not affect significantly the staphylococcal counts. S. aureus growth occurred in all lots made without starter culture. Levels of S. aureus greater than (log10) 7 cells/g were observed in 27/47 and 7/46 cheeses made with pasteurized and raw milk, respectively. Enterotoxins A, B and C were detected in 10/16 and 0/4 cheeses made with pasteurized and raw milk, respectively, and more often in cheeses made without starter than with starter culture. This study demonstrated the need for more uniform manufacturing practices, use of starter culture and use of pasteurized milk only.