The bacterial flora of raw bulk tank milk of fourteen farms in the Winnipeg area

Abstract

The types of bacteria found in the raw bulk tank milk of fourteen farms in the Winnipeg area were determined over a ten month period, from 7-9 samples per farm, by plating in duplicate on Standard Plate Count Agar, incubating for 48 hrs. at 32o C, and picking 25 colonies at random from each countable plate for detailed study. Pure cultures were separated on the basis of the Gram stain, catalase test, coagulase test, gas production in lactose, and spore stain into eight categories. Of the 5550 pure cultures studied, 51.4% were micrococci, 20.0% Gram -ve rods, 19.2% streptococci, 2.7% asporogenous Gram +ve rods, 2.2% coliform organisms, 2.0% staphylococci, 0.2% bacilli, and less than 0.1% lactobacilli. The fourteen farms used in the study were classified as "good", "fair", or "poor" on the basis of the cleanliness as determined by visual examination of equipment surfaces with which the milk had come in contact. As conditions on the farm deteriorated, the percentage of streptococci gradually increased, while the percentage of Gram -ve rods gradually decreased. However, the milk samples of several farms possessed a characteristic flora irrespective of the colony count or the cleanliness of the equipment with which the milk had been handled.