Beta-lactamase producing bacteria in the human oral cavity.

Twenty-six individuals who had no history of long-term antibiotic therapy were examined for the prevalence of beta-lactamase producing bacteria in the oral cavity. Samples from a total of 159 normal and diseased periodontal sites, 44 cheek mucosae, 22 tongue dorsa and 22 salivas were studied. Penicillin resistant organisms were recovered from Trypticase soy blood agar plates containing 1.3 microgram/ml or 2 microgram/ml Benzylpenicillin. Beta-lactamase formation by these isolates was determined using a micro-iodometric assay. Low levels of penicillin resistant organisms were found in all samples. Approximately 10% of the samples yielded Beta-lactamase producing strains. Except for a few Veillonella parvula strains, all Beta-lactamase forming isolates were members of the Bacteroides melaninogenicus subspecies melaninogenicus - Bacteroides oralis group of organisms. These species can produce severe infections and, therefore, the present findings may be important in the clinical management of oral and nonoral infection.

In vitro antimicrobial susceptibility of Actinobacillus actinomycetemcomitans.

The agar dilution technique was used for determination of the antibiotic susceptibilities of 57 oral isolates and 2 nonoral isolates of Actinobacillus actinomycetemcomitans. Tetracycline, minocycline, and chloramphenicol inhibited more than 96% of the strains tested at a concentration of less than or equal to 2 micrograms/ml; 89% of the strains were inhibited by 2 micrograms of carbenicillin per ml. The other antimicrobial agents tested were less active. Approximately 10% of the A. actinomycetemcomitans strains were resistant to ampicillin, erythromycin, and penicillin G at concentrations of 32 to 64 micrograms/ml. These data suggest that tetracycline and minocycline may be valuable drugs in the treatment of A. actinomycetemcomitans infections.