Background: Antibiotics are more and more frequently prescribed in dentistry for prevention and treatment of oral diseases. Bacterial resistance to these agents is clearly increasing, including even previously susceptible microorganisms and true pathogens. The aim of the present investigation was to examine resistant bacterial strains with respect to possible multiple antibiotic resistance.
Methods: In a previous investigation, implant-associated bacteria were tested first as mixed cultures and again as pure isolates (n = 138) for resistance to one of five antibiotics (ampicillin/AM, ampicillin + sulbactam/AB, azithromycin/AZ, penicillin/PG, moxifloxacin/MX) using the Etest®. The resistance of most of the pure isolates was lower than in mixed culture, but 31.2% had retained their original resistance. Subsequently, all 138 isolates were tested for resistance or susceptibility to the other four antibiotics, again using the Etest®.
Results: 27.6% (38/138) of the isolates retained their original antibiotic resistance and were resistant to at least one other antibiotic (MIC ≥ 128 μg/mL for AB, AM or AZ, ≥ 32 μg/mL PG, ≥ 24 μg/mL MX). 2.2% (3/138) strains had lost their original antibiotic resistance, but were resistant to at least one other antibiotic (MIC ≥ 128 μg/mL for AB, AM, or AZ, ≥ 32 μg/mL PG, ≥ 24 μg/mL MX).
Conclusions: Some of the isolates belonging to the implant-associated microflora were multi-resistant, even though the patients had not received any antibiotics six weeks prior to the sampling. The exact mechanisms that lead to multiple resistance need to be examined in further studies.