RESUMO
In 23 untreated adult periodontitis patients, the occurrence of beta-lactamase producing periodontal bacteria was determined. In addition to non-selective isolation media, selective isolation and growth of beta-lactamase positive subgingival bacterial species was carried out on blood agar plates supplemented with amoxicillin and plates with amoxicillin+clavulanic acid. Porphyromonas gingivalis, Prevotella intermedia, Actinobacillus actinomycetemcomitans, Peptostreptococcus micros, Fusobacterium nucleatum, Bacteroides forsythus and Campylobacter rectus isolates from the non-selective medium were tested for beta-lactamase activity by a nitrocefin disk method (DrySlide) and by a laboratory chromogenic nitrocefin-based test. Isolates from the amoxicillin plates that were absent on the amoxicillin/clavulanic acid plates were identified and tested for beta-lactamase production. Based on the non-selective plates, six of 23 P. intermedia isolates, 2 of 19 B. forsythus isolates and 3 of 23 F. nucleatum isolates were beta-lactamase positive. The beta-lactamase positive species Prevotella loescheii, Prevotella buccae, Prevotella buccalis and Actinomyces spp were recovered from the selective amoxicillin plates. beta-Lactamase positive subgingival species were recovered from 17 of 23 patients (74%) but usually comprised low proportions of the subgingival microbiota (range < 0.01-15%). Comparison of the DrySlide test and the nitrocefin-based laboratory test revealed full agreement of test results. beta-Lactamase activity in whole subgingival plaque was detected in 12 patient samples (52%). It was concluded that beta-lactamase activity in subgingival bacteria in adult periodontitis is a common feature. However, since the majority of the samples showed only low-level enzymatic activity, the clinical relevance of this observation with regard to therapy with unprotected enzyme-susceptible beta-lactams is uncertain, though failure on the other hand, is difficult to rule out when a mechanism of resistance is present. The majority of beta-lactamase positive strains was found among species of the Prevotella genus.