THERMO-TOLERANT ORGANISMS AS A CAUSE OF SO-CALLED PIN-POINT COLONIES

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Abstract
A review of the literature, together with a general discussion of the importance of pin point colonies in numerical estimations of bacteria in dairy products. From dairy products, a large number of cultures were isolated which produced pin point colonies and were shown to withstand 63[degree]C. for several hrs. They were thermo-tolerant and not thermophilic, since they would not grow at pasteurizing temperatures, and were also obligate saccharophilic. The small amount of sugar carried over in the 1-100 dilution in plating on plain agar was sufficient to induce growth. The expected number of pin point colonies failed to appear in the 1-1000 and higher dilutions, due to absence of sugar; however, introduction of the same amount of sugar as in a 1-100 dilution caused the expected number of colonies to appear. Resistance to heat was shown by the fact that, on the average, 99.84% survived the 1st pasteurization, 72% the 2nd, and 46% the 3rd. Organisms of this type were successfully isolated from 47% of the dairy products examined (cream, whole milk, skim milk). Cultural and morphological studies are reported and used as a basis for dividing the strains into various sub-groups, all non-spore-formers.