Various bacteriological, peptones were studied as to effects on enumeration of pasteurization-resistant bacteria in milk. No appreciable differences were observed in colony counts of unheated cultures of thermoduric Micrococcus varians and Arthrobacter and Streptococcus sp. when plated with media containing different peptones. After laboratory pasteurization, colony counts differed substantially. Usually, media producing the highest counts yielded the largest and most easily discernible colonies. Bacto-Tryptone was deficient for colony development of thermoduric streptococci. Results indicate that, although seemingly adequate for enumeration in raw milk, the bacteriological peptone currently recommended for the standard plate count may not be satisfactory for the determination of the maximum viable bacteria population of pasteurized milk.
1Journal Paper No. J-5304 of the Iowa Agricultural and Home Economics Experiment Station, Ames, Iowa. Project No. 1050.
2Present address: Department of Food Science and Technology, University of California, Davis.
3Present address: Department of Dairy Science, University of Arizona, Tucson.
4Sheffield Chemical, Norwich, N. Y.