Comparison of Different Methods of Identification of Streptococcus Mutans Clinical Isolates

Abstract

Streptococcus mutans is a key pathogen in dental caries. This species is also implicated in extra-oral pathologies. The efficient evaluation of identification methods for Streptococcus mutans is therefore clinically relevant to determine the risk of caries and to identify its presence in other extra-oral diseases where it is involved.The objective of this study was to compare the accuracy of different methods for identification of Streptococcus mutans.For this, saliva samples obtained from patients with Parkinson's disease, enrolled in a clinical trial, were plated on Mitis Salivarius Agar medium supplemented with potassium tellurite, bacitracin and kanamycin (MSKB). After incubation, S. mutans colonies were identified on the basis of their differential morphological characteristics and Gram staining was performed. After these steps, strains with characteristic S. mutans morphology were subjected to molecular biology techniques (several PCR methods) and proteomic identification by MALDI-TOF mass spectrometry. Finally, the 49 strains were sequenced to confirm the identifications obtained with the previous methodsThe results showed that culture on MSKB allowed the recovery of various oral streptococcal species. 95.9% of S. mutans were correctly identified after proteomic identification. Among the PCRs tested, two different techniques resulted in correct identification of the strains.It was concluded that for morphological identification of S. mutans, the MSKB culture medium used in this study was not selective to a sufficient extend. On the other hand, some PCR methods seemed to be a good solution while MALDI-TOF mass spectrometry can lead to rare identification errors. Except for sequencing, the main limitation of the tested methods was the lack of detection of contaminating bacteria in clinical isolates.

Note:
Funding declaration: This work was partially supported by France Parkinson

Conflict of Interests: The authors declare no conflict of interest.

Ethical Approval: The research protocol was approved by the institutional Ethics Committee, and all the participants signed a written informed consent form.

Keywords: Streptococcus mutans, identification, MALDI-TOF, PCR