Inhibitory effect of aqueous garlic (Allium sativum) extract on multi-drug-resistant Streptococcus mutans species: an in vitro study

Introduction: Garlic (Allium sativum) extract has an inhibitory effect on various pathogenic bacteria, viruses and fungi. The aim of the present study was to evaluate in vitro inhibitory effect of garlic extract on multi-drug-resistant (MDR) strains of Streptococcus mutans isolated from human carious teeth. Filtered sterilized aqueous extract of garlic was used in the present study.Materials and methods: In this in vitro case-control study data was analyzed with Student’s t-test (α = 0.05). From 105 extracted human carious teeth 92 strains of S mutans were isolated. Disk sensitivity tests and broth dilution methods were used to determine antibiotic sensitivity profile and inhibitory activity of garlic extract on S mutans.Results: Among 92 isolates of S mutans, 28 (30.4%) were MDR since they were resistant to four or more antibiotics. The highest and least resistance rates were observed for tetracycline (30.4%) and teichoplanin and vancomycin (0%), respectively; on the other hand, 22.8% and 23.9% of the isolates were resistant to penicillin and amoxicillin, respectively. Chlorhexidine minimum inhibitory concentration (MIC) for MDR and non-MDR S mutans varied from 2 to 16 µg/mL and from 0.25 to 1 µg/mL, respectively (p value < 0.05). All the isolates, MDR and non-MDR, were sensitive to garlic extract with the MIC ranging from 4 to 32 mg/mL. Conclusion: Considering the data obtained from the present study, mouthwashes or toothpastes containing optimum concentrations of garlic extract can be used for the prevention of dental caries.Key words: Dental caries, Garlic extract, Multi-drug-resistant, Streptococcus mutan