Growth of Micro-organisms from Supragingival Dental Plaque on Saliva Agar

The role of saliva in supporting the growth of dental plaque has scarcely been investigated. We have studied the growth and recovery of micro-organisms from dental plaque samples on saliva-agar plates, prepared from filter-sterilized wax-stimulated whole saliva. Under optimal conditions, the mean recovery of plaque samples on saliva agar was about 50% (range, 22-77) of the recovery on blood agar. Addition of 2.5 mmol/L dithiothreitol (DTT) strongly facilitated filter-sterilization of saliva, but DTT concentrations higher than 1 mmol/L reduced the recovery of plaque micro-organisms on saliva agar. Catalase (100 U/ml) offered protection against the inhibitory effect of DTT. Addition of glucose (1-5 mmol/L) increased only slightly the recovery of plaque micro-organisms on saliva agar. When supragingival plaque was plated on saliva- and blood-agar plates, the composition of the microflora isolated from saliva agar strongly resembled that isolated from blood agar. The predominant species — i.e., Streptococcus and Actinomyces — all grew on saliva agar though usually in numbers somewhat lower than those on blood agar. In addition, most species normally found only in low proportions in supragingival dental plaque were also found to grow on saliva agar. Collectively, the results lead to the conclusion that the supragingival microflora can utilize saliva as a complete source of nutrients.