EFFECT OF THE TYPE OF BACTERIOLOGICAL PEPTONE IN THE PLATING MEDIUM UPON THE ENUMERATION OF PASTEURIZATION-RESISTANT BACTERIA IN MILK1

Abstract

Summary 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.