Bacteriological Indices of the Sanitary Quality of Market Cream

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Abstract
The authors found through a comparative study of methods for the enumeration of bacteria in raw retail cream samples, import cream samples and retail pasteurized cream samples that the direct microscopic count is the most satisfactory and practical method for determining the sanitary quality of market cream. The so-called standard plate count is less satisfactory than plate counts made at lower temps. Plate counts at higher temps. for thermophilic organisms were of significance for certain samples but of little value for routine testing. The advantage of the direct count over the standard plate count lies in the procurement of data on types of organisms present, giving directional guidance to corrective control measures. In a large number of cases the results of the direct count agree with results of coliform tests that indicate improper handling after pasteurization, when plate counts seemingly indicate cream of good quality. Market cream may contain appreciable numbers of sporogenic bacilli able to survive for 30 min. temps. considerably higher than that of pasteurization, and these organisms are capable of rapid development in cream at room temp. In many cases multiplication occurs at a somewhat slower rate even at refrigerator temp. Such organisms are detected by direct microscopic count but do not ordinarily produce colonies on plates of "standard methods" agar incubated at 8[degree] C, 20[degree] C, or 37[degree] C, and only rarely at 55[degree] C.