Gram-positive oral bacteria as reservoirs of transferable antimicrobial resistance genes in dentistry

Background: The oral cavity is a complex microbial ecosystem that acts as a reservoir of antimicrobial resistance genes associated with antibiotics used in dental practice, particularly in Gram-positive bacteria. Aims: This study aimed to analyze antimicrobial resistance genes in oral isolates of Streptococcus, Staphylococcus, and Enterococcus. Materials and Methods: Two hundred and fifty isolates were analyzed. Microbiological identification and antimicrobial susceptibility tests were performed using MicroScan in accordance with the Clinical and Laboratory Standards Institute guidelines. Polymerase chain reaction was used to detect resistance genes; blaZ, erm, mef, msrA, lnu, and aac (6’)-aph (2”). Statistical Analysis: Descriptive statistics were applied to assess phenotypic resistance, co^-resistance and multidrug resistance (MDR). Gene co-occurrence patterns were evaluated using heatmap analysis in Python (Seaborn). Results: Resistance was primarily associated with blaZ (n = 70). Co-resistance occurred in 15 isolates, most commonly blaZ + aac (6’)-aph (2”) (4 cases). MDR occurred in 7 isolates, with mecA + mef + lnu + aac (6’)-aph (2”) as the most frequent pattern (n = 2). The co-occurrence of genes revealed recurrent associations between β-lactam, macrolide–lincosamide–streptogramin and aminoglycoside resistance determinants. Conclusions: The oral cavity acts as a reservoir of transferable antimicrobial resistance genes in Gram-positive bacteria, with co-resistance and MDR patterns relevant to dental practice.