Bacteriological Evaluation of Manufacturing-Grade Bulk-Tank Milk

Abstract

The standard plate count (SPC) of 37.7% of 701 manufacturing-grade bulk-tank milk samples exceeded 1,000,000/ml; 26.5% of the psychrophilic plate counts exceeded this level also. Thermoduric plate counts in excess of 10,000/ml were obtained on 43. 6% of the samples. The direct microscopic count was less than the SPC by a considerable margin on many samples. In 245 samples out of 586 comparisons where the results of these 2 counts failed to agree, all but 16.3% had high psychrophilic and/or thermoduric counts. Most psychrophilic isolates stained readily, but many grew in clumps.