Antibiotic susceptibility testing of subgingival plaque samples

Area of Science:

• Microbiology
• Periodontology
• Pharmacology

Background:

• Periodontal disease involves bacterial infection requiring effective antimicrobial therapy.
• Antibiotic selection for adjunctive periodontal therapy is crucial for treatment success.
• Understanding in vitro antimicrobial susceptibility patterns can guide clinical choices.

Purpose of the Study:

• To determine the in vitro inhibitory effects of various antimicrobial agents on dental plaque bacteria from periodontally diseased sites.
• To aid in selecting appropriate antibiotics for adjunctive use in periodontal therapy.
• To assess the impact of prior antibiotic treatment on bacterial susceptibility.

Main Methods:

• Dental plaque samples were collected from two groups of patients with varying severity of periodontal disease.
• Bacterial isolates were tested in vitro against a battery of antibiotics incorporated into agar media.
• Antibiotic concentrations mimicked those achieved in gingival fluid or blood after standard oral dosages.
• Inhibitory effect was quantified by comparing bacterial recovery on antibiotic-containing media versus basal media.

Main Results:

• Penicillins (except cloxacillin) were most effective; benzylpenicillin inhibited 90%, ampicillin and amoxicillin inhibited over 99% of isolates.
• Tetracycline showed good inhibition (≥90%) in untreated patients, but resistance was common in previously treated individuals.
• Clindamycin was effective against ≥90% of organisms in most samples, including tetracycline-resistant ones.
• Erythromycin was largely ineffective in severe cases, while metronidazole showed minimal efficacy at tested concentrations.

Conclusions:

• Penicillins are highly effective in vitro against subgingival plaque bacteria relevant to periodontal disease.
• Prior antibiotic exposure significantly influences bacterial susceptibility, particularly to tetracycline.
• No single agent consistently inhibited all tested bacteria, highlighting the need for tailored antimicrobial strategies.