Enumeration of bacteria in raw milk: Evaluation of various techniques

Lachowsky, William M.
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University of Guelph

The enumeration of bacteria in bulk tank raw milk samples is part of the Raw Milk Quality Testing Program of the Ontario Ministry of Agriculture, Food and Rural Affairs to ensure compliance with the Milk Act. The present testing is performed at the University of Guelph, Laboratory Services Division in Guelph, Ontario. The official test is the Plate Loop Count which uses a semi-automated instrument the Petrifoss. This instrument has been in use since 1984. The present bacterial penalty limit is log 5.00 CFU/mL Plate Loop Count incubated at 32\sp∘C for 48 hours. The manufacturers of the Petrifoss (Foss Electric, Hillerod Denmark) no longer manufacture the instrument, supply spare parts or provide technical support. An evaluation of the different techniques and instruments which have been used to enumerate bacteria in raw milk was undertaken. Three cultural techniques were evaluated: the Standard Plate Count, the Plate Loop Count, and the Spiral Plate Count. All three systems had good correlation coefficients and small standard error of repeatability. (Abstract shortened by UMI.)

enumeration, bacteria, bulk tank raw milk samples, Raw Milk Quality Testing Program, compliance, Milk Act, Plate Loop Count, Petrifoss, Standard Plate Count, Spiral Plate Count