Monitoring the microbiology of high quality milk by monthly sampling over 2 years

The concentrations of seven types of microorganism in the milk produced by farms using high quality milking procedures were monitored monthly. The most commonly encountered bacterium was Pseudomonas, whose concentration varied greatly between samples, but lactococci, lactobacilli and yeasts were also present at more stable concentrations. Staphylococcus aureus and beta-glucuronidase-positive Escherichia coli were occasionally detected. Listeria monocytogenes was found in the samples from only one farm, while Yersinia enterocolitica was never detected. There were seasonal variations in the concentrations of lactobacilli and yeasts over the 2 years monitored. The changes in certain bacteria (Lactococcus, Lactobacillus) on any given farm were very similar from one year to the next. The microbiological characteristics of the milk from the farms examined seemed to be fairly constant. The profiles of some bacteria used for cheesemaking were relatively stable over time. It thus seems that the milk provided by different producers could be typed.