REPLICATE PLATING - DOES IT INCREASE RELIABILITY

As a part of a clinical study to evaluate the antibacterial effect of a topically applied erythromycin gel, microbiological specimens were t aken from two groups of patients: one group using 2% erythromycin gel and the other group using a placebo gel. These specimens were plated i n triplicate using a common source on bacteriological media using stan dard procedures. After the appropriate incubation times, the numbers o f aerobic and anaerobic organisms were counted separately from each of three plates. A comparison of the bacterial colony counts from the re plicate plates showed a high degree of similarity for each type of org anism. Tests for treatment differences in organism counts were perform ed based on single, double and triplicate plating. The results obtaine d were almost identical, suggesting that replicate plating from a comm on source is no more accurate than single plating. The only apparent a dvantage of this type of replicate plating is heightened confidence in the reliability of bacterial counts from single plates.