Growth ofStreptococcus pyogenesin milk stored at atmospheric temperatures

Abstract

1.Streptococcus pyogenesmultiplies readily in sterilized milk stored at 22 and 18° C., and more slowly at 15° C. In fresh raw milk this organism begins to multiply slowly only after 48–72 hours of storage at 18–22° C. In laboratory pasteurized milk the result is similar, but both commercially pasteurized milk and raw graded milk bottled for distribution sour too rapidly for multiplication to take place after artificial contamination. These facts suggest that widespread epidemics are rarely due to extensive multiplication ofS. pyogenesin milk during commercial or household storage.2. The initial degree of contamination of milk withS. pyogeneshas no influence upon this organism's ability to multiply during storage.3. The failure ofS. pyogenesto multiply during storage is due to (a) its natural reluctance to grow at atmospheric temperatures, (b) the bacteriostatic action of the milk, and (c) the readiness with which saprophytic bacteria multiply at atmospheric temperatures.4. It is contended that infected cows play a major part in the spread of milk-borneS. pyogenesepidemics, and relevant literature is quoted to support this view. It is urged that routine investigation of apparent milk-borne epidemics should include the immediate bacteriological examination of an individual sample of milk from every cow concerned in the supply under suspicion.