Mitis-salivarius (MS) agar has been used widely in microbial epidemiological
studies because oral viridans streptococci can be selectively grown on this medium. Even
though the previous findings reported the limited selecting power of MS agar for streptococcus
strains, the identities of non-streptococcal strains from human oral samples which
can grow on this medium are not clear yet. In this study, we identified non-streptococcal
organisms grown on MS agar plates by polymerase chain reaction (PCR) amplification and
sequencing of the 16S ribosomal RNA (rRNA) gene.
Design: Eighty bacterial colonies on MS plates were isolated from plaque samples, and
bacterial identification was achieved with the rapid ID 32 Strep system and mini API reader.
The bacterial colonies identified as non-streptococci by the API system were selected for
further identification. The 16S rRNA gene was amplified by PCR and verified using DNA
sequencing analysis for identification. Sequences were compared with those of reference
organisms in the genome database of the National Center for Biotechnology Information
using the Basic Local Alignment Search Tool (BLAST).
Results: Among the 11 isolated non-streptococcal strains on MS plates, 3 strains were
identified as Actinomyces naeslundii, 7 strains were identified as Actinomyces oris and 1 strain
were identified as Actinomyces sp. using Blastn.
Conclusions: In this study, we showed that some oral Actinomyces species can grow on
Streptococcus-selective MS agar plates.