Macrolide-resistant Streptococcus mutans in dental caries patients in Iraq

Background: Dental caries is a globally prevalent chronic infectious disease primarily caused by Streptococcus mutants, a bacterium with strong acid-producing and acid-tolerant capabilities. The growing antimicrobial resistance of S. mutants, particularly to macrolides such as azithromycin and erythromycin, poses a significant clinical challenge. Objectives: this study aimed to investigate the prevalence of macrolide resistance and associated resistance gen (mefA, ermB) in S.mutans from dental caries patients and to evaluate their biofilm-forming ability. Methods: one hundred dental plaque samples were collected from patients with dental caries. Morphological, biochemical, and molecular methods characterized the isolates. Antimicrobial susceptibility was tested by the disk diffusion method. macrolide resistance gen mefA and ermB wer found by polymerase chain reaction (PCR). Biofilm production, the ability to form biofilm, was determined according to the crystal violet microtiter plate method. Results: Among the 100 sample examined, 50 isolates were identified as S. mutans. Of these,33%were resistant to azithromycin and carried mefA. Furthermore,40% of the five presumptive isolates were positive for the ermB gene. moste of the resistant isolates were strong biofilm producers. Conclusion: The presence of the mefA and ermB genes in macrolide-resistant S.mutans strains indicates the involvement of efflux mechanisms and ribosomal protection in macrolide resistance. Furthermore, these resistant isolates are strong biofilm producer, wich makes the treatment more difficult. These results highlight the importance of routine molecular monitoring and a more judicious use of antibiotics in dental-related health care.