Abstract:
Introduction: Dental caries, primarily caused by Streptococcus mutans, poses a global
oral health challenge. Early detection of antibiotic resistance patterns in Streptococcus
mutans and implementation of effective prophylactic therapy is crucial for the prevention
of systemic complications, including infective endocarditis.
Objective: To isolate Streptococcus mutans from dental caries in patients attending Dental
clinic, Teaching Hospital, Jaffna and to evaluate their antibiotic sensitivity pattern.
Methodology: A study was conducted among 120 patients selected by systematic
sampling method from the Dental clinic, Teaching Hospital, Jaffna during September-
October 2023. Samples were collected and transported in Brain Heart Infusion broth to the
laboratory within 1-2 hours and incubated at 37°C for 24 hours inside the 5-10% CO2
incubator. Samples were plated on Mitis Salivarius agar with bacitracin 0.2U/mL and 20%
sucrose. Streptococcus mutans strains were identified based on their characteristic colony
morphology compared with standard strain (ATCC 700610) grown on the same medium.
Selected colonies were confirmed by Gram staining and biochemical tests. Antibiotic
susceptibility test was performed by using Amoxicillin (25μg), Co-amoxiclavulanic acid
(30 μg), Erythromycin (15 μg) and Clindamycin (2 μg) by using CLSI guidelines.
Results: Among 109 positive cultures, Streptococcus mutans were isolated from 84 (70%)
samples. The highest susceptibility was observed for Amoxicillin with a 33.96 ± 6.5 mm
mean zone of inhibition followed by Co-amoxiclavulanic acid with a 32.32 ± 5.9 mm mean
zone of inhibition. Also in our study, the antibiotic resistance rates for Erythromycin were
21.43% and Clindamycin was 16.67%.
Conclusions: Streptococcus mutans is a common pathogen associated with dental caries,
with an isolation rate of 70% (84/120) in this study. Amoxicillin can be used as an effective
antibacterial drug to treat caries. The findings will provide valuable insights into the
microbiology of dental caries, informing preventive and therapeutic strategies.
