[A rapid method of detecting psychrotrophic bacteria in raw milk].

Determination of the counts of psychrotrophic bacteria offers an important indicator of the technological quality of purchased raw milk, and also an indicator of the hygienic level of its production in agricultural primary production, particularly with respect to the sanitation of milking machines. The applied and published methods of determination of the counts of psychrotrophic microbial contaminants have revealed large differences, multiplied by insufficient legislation in this country, by vague and even wrong definition of the given group of bacteria, and/or by the misuse of the concepts psychrotrophic and psychrophil bacteria. Since the level of the microbial quality of raw milk should be increased, we investigated and developed convenient methods of determination of psychrotrophic bacterium counts in the last years (Urbanová et al., 1988; Urbanová, in print): these methods should facilitate the reasonable control applying an expeditious procedure. A long incubation time of standard procedure is a disadvantage complicating the practical use of the previous procedure (10 days at a temperature of 7 degrees C). An accelerated procedure of psychotrophic bacterium cultivation to determine their counts in raw milk is described in this paper. After thorough stirring, a raw milk sample is diluted with sterile physiological solution (pH 7.2) pursuant to the standard CSN 57 0101. The dilutions 10(-2), 10(-3), 10(-4) were the most convenient for inoculation when the counts of psychrotrophic contaminants were determined in raw milk. The dilutions 10(-3), 10(-4), 10(-5) were inoculated if higher milk contaminations were expected.(ABSTRACT TRUNCATED AT 250 WORDS)