Antibiotic Susceptibility Patterns of and Strains from Different Decades.

The aim of this study was to determine the antibiotic susceptibility patterns of 57 and 56 strains isolated from subgingival biofilm samples of periodontitis patients in Switzerland from 1980 to 2017. The minimal inhibitory concentrations (MIC) of the most commonly used antibiotics in periodontal therapy (amoxicillin, metronidazole, azithromycin, and doxycycline) or in severe body infections (amoxicillin/clavulanic acid, clindamycin, ertapenem, and moxifloxacin) were determined. Furthermore, all the strains were screened for beta-lactamase activity and the presence of selected resistance genes (A, F, and Q). Overall, there was no significant increase in MIC values over the 37‑year period. Two of the most recent isolates yielded the highest MIC values. The first isolate was F-positive with MIC values >8 µg/mL, 2 µg/mL, and 0.25 µg/mL for clindamycin, azithromycin, and moxifloxacin, respectively. The second isolate showed a high MIC value of 4 µg/mL for moxifloxacin, which was associated with a confirmed single-point mutation in the quinolone resistance-determining region (QRDR) of the A gene. Although there was no significant increase in the antibiotic resistance among the oral bacterial isolates tested, the detection of resistant isolates underlines the need to optimize the antibiotic therapeutic protocols in dentistry.