A preliminary study of mecA gene expression and methicillin resistance in staphylococci isolated from the human oral cavity

Introduction: Staphylococci are common human commensals that acquire methicillin resistance via the mecA gene. Methicillin resistance in staphylococci from various clinical sources has been assessed using cefoxitin disc diffusion test (CDDT) and PCR detection of the mecA gene. However, oral staphylococci have been studied less frequently compared with other clinical sources. There are no previous studies on methicillin resistance in oral staphylococci in Sri Lanka.

Objective: This study aimed to demonstrate methicillin resistance in staphylococci isolated from the human oral cavity using CDDT and PCR detection of mecA gene.

Materials and methods: Twenty-five oral isolates of staphylococci were selected after confirming their identity using colony morphology, Gram stain, catalase test, and the coagulase test. Further authentication of identity was obtained using amplification of the 16S rRNA gene. Methicillin resistance was demonstrated using CDDT and PCR detection of the mecA gene.

Results: There were 7 (28%) isolates of coagulase positive (presumed S. aureus) and 18 (72%) of coagulase negative staphylococci (CoNS). All the coagulase positive isolates were methicillin sensitive. Within the 18 CoNS, 2 (11%) were methicillin resistant and were found to carry the mecA gene using PCR.

Conclusion: Coagulase positive and negative staphylococci with or without methicillin resistance may colonize the human oral cavity. Coagulase negative staphylococci were the majority in this limited study. Further studies are warranted to determine the incidence of staphylococci in the oral cavity and their antimicrobial sensitivity.