Using Selective Agar Containing Ciprofloxacin and Tetracycline Reveals Resistant Oral Microbiota in Healthy and...

The oral cavity may act as a reservoir for antibiotic resistance. This study aimed to directly isolate and identify phenotypically resistant bacteria from the oral biofilm of healthy individuals and patients with periodontitis, using tetracycline, and ciprofloxacin containing selective agar. Furthermore, resistance of selected bacteria towards ampicillin was also evaluated. Plaque samples were collected from 12 patients (six healthy, six with periodontitis). Bacteria were cultured on selective agar containg defined antibiotic concentration and non-selective media under aerobic and anaerobic conditions, identified by MALDI-TOF mass spectrometry and 16S rDNA sequencing. The selected bacteria were subsequently tested for susceptibility using disk diffusion, E-test, and β-lactamase assay. 495 strains representing 106 species were isolated, including 54 aerobes/facultative anaerobes and 52 obligate anaerobes. Antibiotic resistance was observed in all subjects: 15.2% of isolates were resistant to tetracycline, 32.9% to ciprofloxacin, and 0.6% to ampicillin, with no significant differences between healthy and periodontitis groups. Tetracycline resistance was most frequent in the Streptococcus mitis group and Eubacterium spp., while ciprofloxacin resistance was dominated by Actinomyces-Schaalia group. Concluding, prevalence of antibiotic-resistance was comparable between healthy and periodontitis patients. Resistance was most prevalent against ciprofloxacin and tetracycline, highlighting the oral cavity as a relevant reservoir for antibiotic resistance.