640. Some bacteriological aspects of commercially sterilized milk: II. Type of sporeforming bacteria isolated

Abstract

Cultures of sporeforming bacteria isolated from commercially sterilized milk were examined and seasonal variations in the incidence ofB. subtilis/B. licheniformisstrains were apparent which may account for the increased rate of spoilage at 30° C. during the winter.B. subtiliswas the most common mesophilic sporeformer isolated, and under favourable conditions it produces rapid digestion of milk.Thermophilic sporeformers are frequently present, and usually produce a firm acid clot in milk held at temperatures favourable for their growth. The classification of the thermophiles isolated is uncertain and a review of the classification of the aerobic thermophilic sporeformers in general is required.Cl. thermosaccharolyticum, a gas-producing thermophile, was isolated from sterilized milk.

The alcohol test applied to sterilized milk

“…The alcohol test applied to sterilized milk 265 from these results that a positive 80 % alcohol test after 24 h at 37 °C is of little value in predicting whether growth will occur at 22 °C within 3 weeks, except possibly with B. ce.re.us which has been isolated only occasionally from commercial sterilized milk (Grinsted & Clegg, 1955;Ridgway, 1955;Candy & Nichols, 1956). Tierie (1953) suggested that a satisfactory sample of sterilized milk should not clot on boiling, nor contain more than 1000 bacteria/ml after incubation at 37 °C for 3 days.…”