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The prevalence and populations of Porphyromonas and Prevotella species were determined in three samples of dental plaque from each of 34 healthy dogs. Porphyromonas gingivalis was present in 68 per cent of the dogs and 47 per cent of the plaque samples. The counts of P gingivalis increased with age (P < 0.1), the amount of plaque (P < 0.05) and the degree of gingivitis (P < 0.1). Prevotella intermedia was present in 44 per cent of the dogs and 23 per cent of the plaque samples. The counts of P intermedia were correlated with the amount of plaque (P < 0.05) and the degree of gingivitis (P < 0.1). Porphyromonas canoris, P salivosa, P cangingivalis, P cansulci, P crevioricanis and Prevotella denticola were isolated from only 9, 6, 3, 3, 3 and 3 per cent of the dogs, respectively. Porphyromonas gingivicanis was not isolated from any of the animals sampled. There was a highly significant (P < 0.001) correlation between the amount of plaque, the extent of gingivitis and the age of the dog.

Helicobacter pylori is rarely cultured from sites other than the gastric mucosa. The morphology of H. pylori in the stomach and dental plaque of adult dyspeptic patients was investigated to determine whether a difference in morphology at these sites could explain the inability to culture the organism from the oral cavity. Five adult patients attending for an upper gastrointestinal endoscopy were investigated. Dental plaque and gastric antral biopsy samples were analysed by culture and polymerase chain reaction (PCR) both before and after immunomagnetic separation using polyclonal rabbit anti-H. pylori IgG. Bead:bacteria aggregates were then examined by scanning electron microscopy (SEM). Rod and coccoid forms of H. pylori were seen by SEM in all oral and gastric samples which were H. pylori PCR positive. Although rod and coccoid forms have previously been shown to be associated with the gastric mucosa, this is the first time H. pylori cells have been visualized in dental plaque.

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RI, one of the major extracellular arginine-specific proteases of Porphyromonas gingivalis is a heterodimer composed of catalytic (alpha) and adhesin (beta) chains, encoded by the gene prpR1. The distribution of prpR1 and its variation within 43 isolates of P. gingivalis was determined. Chromosomal DNA was digested with Sma I and probed with a 32P-labeled DNA fragment from within the coding region for the alpha component of P. gingivalis W50. All isolates gave the expected 3.2 kb band, corresponding to the coding region for the alpha and beta components. The presence of a second locus (prR2) homologous to the alpha region of prpR1 was also detected. The 1.7-kb alpha coding region of prpR1 was amplified for subsequent restriction analysis. Following Taq I restriction all isolates gave identical patterns. With Rsa I, the majority of isolates (77%) could be placed into a single group. In conclusion, the prpR1 and prR2 loci are maintained in natural populations of P. gingivalis, and only minor polymorphism is detectable within the catalytic domain.