The aim of this study was to determine the
antibiotic susceptibility patterns of 57 Aggregatibacter actinomycetemcomitans and 56 Porphyromonas gingivalis 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 (cfxA, ermF, and tetQ). Overall, there was no significant increase in MIC values over the 37‑year period. Two of the most recent P. gingivalis isolates yielded the highest MIC values. The first isolate was ermF-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 gyrA gene. Although there was no significant increase in the antibiotic resistance among the oral bacterial isolates tested, the detection of resistant P. gingivalis isolates underlines the need to optimize the
antibiotic therapeutic protocols in dentistry.