Molecular identification of Streptococcus mutans and Streptococcus sobrinus from un-stimulated saliva and their association with dental caries and orthodontic appliances

Abstract

Background: Oral streptococci, particularly Streptococcus mutans (S. mutans), have been associated with several diseases affecting multiple anatomical sites. Streptococcus mutans and Streptococcus sobrinus (S. sobrinus), which belong to the Mutans streptococci group, are examples of Gram-positive bacteria that demonstrate facultative anaerobic growth characteristics. These bacteria are frequently seen as members of the native oral microbiota and are largely recognized as the primary causative agents of dental caries. Objective: To molecularly identify S. mutans and S. sobrinus using PCR and investigate their relationship with the caries status and orthodontia appliances. Method: The cross-sectional study, which was conducted in Baghdad from February 2021 to November 2022, involved 359 un-stimulated saliva samples from 340 participants were collected and processed immediately by culturing anaerobically (37°C/72 h) on Mitis Salivarius Bacitracin Agar (MSB-Agar). Morphological characteristics of the colonies, Gram stain were achieved for the bacterial growth. DNA extracted from cultured bacteria. S. mutans and S. sobrinus were identified molecularly by amplifying gtfB and gtfI, respectively, from DNA samples using conventional PCR. Results: From 279/ 336 (83.04%) bacterial DNA samples, 118/279 (42.29%) were positive for S. mutans gtfB and/or S. sobrinus gtfI; S. mutans 84/118 (71.2%), S. sobrinus 6/118 (5.1%) and mixed S. mutans/S. sobrinus 28/118 (23.7%). The results of association between molecular identification of S. mutans with dental caries and missing teeth features of individuals were statically not significant (0.068 and 0.323 > 0.05, respectively), while was significant with filling teeth and orthodontic appliance (0.020, 0.027 < 0.05, respectively). The relationship between molecular identification of S. sobrinus and dental caries, missing, filling teeth and orthodontic were statistically not significant (0.069, 0.975, 0.845 and 0.458 > 0.05), respectively. The relationship between molecular identification of mixed S. mutans/S. sobrinus with dental caries was statically significant (0.042 < 0.05). Conclusion: S. mutans was more prevalence; identification and discrimination for S. mutans/S. sobrinus (depending on gtfB and gtfI) by PCR was more efficacy. Mixed S. mutans/S. sobrinus in a reasonable percentage were related with the hard dental caries status. Identification by colony morphology alone was not achievable in this study. Mitis Salivarius agar with Bacitracin (MSB) is extremely selective for S. mutans and S. sobrinus but cannot distinguish them morphologically.