Prevalence and persistence of amoxycillin-resistant bacteria in the dental plaques of adults.

The prevalence and persistence of amoxycillin-resistant organisms (ARO) in the dental plaque of adults was determined. Plaque samples from ten adults, who had not taken antibiotics during the previous 6 months, were screened for ARO on three occasions at intervals of 3 months. The ARO were tested for their susceptibility to amoxycillin and to amoxycillin plus clavulanic acid as well as their ability to produce beta-lactamases. The ARO were found in all subjects on at least one sampling occasion and in 87% of the 30 samples examined. Of the 36 ARO isolated, 33% were yeasts, 19% were staphylococci, 19% Actinomycetes spp. and 14% lactobacilli, whilst seventeen of the isolates produced a beta-lactamase and seven of these were sensitive to coamoxiclav. The proportion of ARO in an individual fluctuated widely over the study period. It is suggested that the ARO are frequently, though transiently, present in low numbers in the plaque of individuals who have not recently received antibiotics.