ROLL TUBES AND AGAR STRIP TUBES FOR THE BACTERIAL COLONY COUNT OF MILK

Abstract

SUMMARY: Roll‐tube colony counts, using the Astell equipment, were lower than the corresponding Petri dish counts with 27 out of 31 raw milks (87%). The difference between the counts by the two methods was greater than 25% of the plate count for 12 (39%) of the samples.When the same dilution of milk was used for both strip‐tube and plate colony counts, about equal numbers of samples gave counts from the strip tubes above and below about the colony count from plates. When, in order to obtain a more reasonable strip‐tube count, the plates and strip tubes were prepared from different dilutions of the milk, the counts from the latter were, with only 3 exceptions out of 35 milks, below those from the former. The difference between the counts was greater than 25% of the plate count for 15 (43%) of the milks, a figure similar to that obtained in comparing roll‐tube and plate colony counts.