A plating procedure simulating conditions in ripening Cheddar cheese was used to isolate microorganisms in young cheese that grow at ordinary ripening temperatures. Forty-one commercial cheese samples, most 7 days old, were obtained from ten Iowa manufacturing plants. Samples were plated in special Trypticase-soy agar, covered with 50 ml of 1.5% (w/v) agar, and incubated at 7.2 C for 3 months. Following incubation, 967 microorganisms were isolated, purified, and characterized. Numbers and percentages of microorganisms were: 475 enterococci, 49.5%; 148 micrococci, 15%; 126 lactic streptococci, 13%, 108 miscellancous gram-positive rods, 11%; 48 associate bacteria (resembling species of Leuconostoc), 5%; 33 miscellaneous gram-negative rods, 3.5%; 24 lactobacilli, 2.5%; and 5 other miscellaneous microorganisms, 0.5%.
Forty-five commercial lactic starter cultures were examined by the same plating procedure. Duplicate plates of each culture were incubated at 7.2 and 21 C. Although agar plate counts were slightly higher at 21 C, they were within the same range, at both incubation temperatures, for most samples. No enterococci were recovered from commercial lactic starter cultures.
1Journal Paper No. J-4919 of the Iowa Agricultural and Home Economics Experiment Station, Ames, Iowa; Project No. 1188.