Incidence of selected ureolytic bacteria in human dental plaque from sites with differing salivary access

Saliva is the main source of urea in the human mouth and may be responsible for the predilection of ureolytic bacteria for certain tooth sites. As a test of this hypothesis, the ureolytic bacteria, Haemophilus parainfluenzae, Actinomyces naeslundii, Actinomyces viscosus and coagulase-negative oral staphylococci, were enumerated in supragingival plaque from various sites in each of 10 subjects. The sites sampled included the maxillary and mandibular incisors (chosen because the lower incisors are more exposed to the submandibular-sublingual secretion than the upper) and the maxillary and mandibular molars (the upper molars being closer to the source of parotid saliva). After dispersion of the plaque samples in saline, subsamples of each suspension were plated on appropriate selective media and other subsamples were taken for nitrogen analysis to measure the amount of plaque sampled. H. parainfluenzae that used urea was present in the largest numbers, A. viscosus was next and A. naeslundii and coagulase-negative staphylococci were least. The staphylococci and H. parainfluenzae were more numerous from mandibular than from maxillary incisors and from maxillary than mandibular molars, a pattern which suggests that salivary access favours their selection. The numbers of A. viscosus and A. naeslundii were not related to salivary access: A. viscosus was most numerous from the maxillary incisors, possibly because this site is normally the most acidic of the four studied and A. viscosus is strongly acidogenic and aciduric; the incidence of A. naeslundii had no relationship with site.(ABSTRACT TRUNCATED AT 250 WORDS)