Isolation and detection of bacterial species on mitis salivarius bacitracin agar from the plaque samples of caries active children

Abstract

Background: In cariology studies, mitis-salivarius-bacitracin (MSB) agar has been commonly considered as the selective medium for Streptococcus mutans growth. The present study was the part of a funded project (a noninferiority randomized controlled trial) which compared the efficacy of a plant extract-based mouth rinse with that of a fluoride mouth rinse on the S. mutans counts of the children. Aim: This study aimed to identify the frequency of detection of S. mutans and nonstreptococcal bacterial species from the dental plaque of caries active children using a combined technique of anaerobic culture and matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry. Settings and Methods: Caries-active children (8–12 years old) were enrolled from a pediatric dental outpatient department at a tertiary care hospital. From each participant, dental plaque samples were collected from carious surfaces under sterilized conditions and then subjected to anaerobic culture. After 48 h of incubation, the bacterial colonies were isolated by sub-culture and identified by the MALDI-TOF. Results: In all, 13 different bacterial species were isolated from the MSB agar medium. Other than S. mutans species, colonies of bacterial species such as Veillonella dispar, Streptococcus anginosus, Veillonella parvula, and Streptococcus gordonii were also frequently observed from the medium. Conclusions: The study concluded that several bacterial strains, both streptococcal and nonstreptococcal, could be isolated from the MSB agar medium; hence, this medium should no longer be considered selective medium for the culture of S. mutans in clinical and epidemiological studies.

Keywords

• anaerobic culture
• matrix-assisted laser desorption ionization-time of flight
• mitis-salivarius agar medium
• nonstreptococcal mutans
• streptococcus mutans