Bacteriological Examination of Oral Material by a Differential Counting Technique

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Abstract
When only very small amounts of inoculum are available, conventional bacterial counting methods become impracticable. A differential counting technique has been developed for such situations, in which the organisms present are spread on a non-selective solid medium and subsequently identified by the appearance of their micro-colonies after a short period of incubation. The count is proportional in principle but can be made absolute if an absolute count can be performed on one of the major groups present. The results obtained suggest that the microflora of the oral surfaces is in a state of continuous change, and the proportion of the different genera vary widely not only from one individual to another but also from the same site at different times and from different sites at the same time. Carious lesions appear to show a proportional increase of lactobacilli and streptococci in their deeper layers.