The widespread use of antibiotics in Spain is reflected in the level of resistance of the subgingival microflora of adult patients with periodontitis.

The purpose of this study was to compare the subgingival microbiota of two geographically distinct patient populations using identical clinical and bacteriological methods. Adult patients with a diagnosis of periodontitis were consecutively selected according to pre-defined clinical criteria. Microbiological samples were taken from the deepest four sites with bleeding. The samples were plated on blood agar plates, for the determination of the total anaerobic counts and identification of specific bacterial pathogens, and on TSBV and McConkey for isolation of Actinobacillus actinomycetemcomitans and enteric rods, respectively. Thirty-one patients in Spain and 30 patients in The Netherlands were selected. Both patient groups showed similar clinical characteristics, both in terms of age, gender and periodontal clinical variables. A. actinomycetemcomitans was significantly more prevalent (23.3% vs. 3.2%) in the Dutch group, while Porphyromonas gingivalis was significantly more prevalent (64.5% vs. 36.7%) in the Spanish group. Bacteroides forsythus and most commensal periodontal pathogens showed similar prevalences, except Peptostreptococcus micros that was significantly more frequent in the Dutch group (96.7% vs. 74.2%). In summary, the subgingival microbiota from the Spanish group was characterised by a high prevalence of P. gingivalis and low of A. actinomycetemcomitans, while the flora from the Dutch group was characterised by a high prevalence of A. actinomycetemcomitans and P. micros.

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.

A high prevalence of beta-lactamase producing bacteria has been evaluated in two distinct populations, belonging to two European countries with clear differences in antibiotic usage policy. A higher prevalence and a more complex beta-lactamase producing microflora, were found in the Spanish group, associated with a higher antibiotic consumption. This study shows that a higher use of beta-lactam antibiotics is reflected in the % of beta-lactamase producing bacteria in the subgingival microflora of patients with periodontitis. This information may be important in the treatment of severe periodontitis.

The subgingival area is a microbial habitat for mutans streptococci that may be of importance in the development of root caries in periodontitis patients.