BEHAVIOR OF STAPHYLOCOCCUS-AUREUS AND OF ESCHERICHIA-COLI AND INJURY FORMATION DURING PRODUCTION AND STORAGE PHASES OF PRATO CHEESE

The behaviour of S. aureus and of E. coli during production and storag e of ''Prato'' (Edam-like) cheese were studied. The product was prepar ed according to the usual procedure. After pasteurization, the milk wa s inoculated with S.aureus FRI A-100 and E. coli ATCC 25922 in concent rations corresponding to 10(6) and 10(7) cells/ml, respectively. The c heeses samples were kept at 12 +/- 2-degrees-C for 5 days followed by storage at 15 +/- 2-degrees-C up to the end of experiment (98 days). I n order to assess cell injury, the S. aureus and E. coli counts were m ade according to the traditional methodologies and those employing a p eriod for recovery of stressed-cells (19). Both pH and acidity were co nstantly determined. S.aureus counts increased during the cheese manuf acture, whereas E. coli remained practically constant. However E. coli counts presented marked decrease since the onset of the ripening on c uring period, with acidity levels, corresponding to 0.60% and 0.70%. O n the other hand, S. aureus counts started to decrease after 21 days a nd corresponding acidity varying from 0.75% to 0.80%. At the end of th ree months ripening, the results indicated decrease in S. aureus and E . coli counts, corresponding to eight and seven to to eight log cycles , respectively. Sub-lethal acid injury was more noticeable on E. coli than on S. aureus..