한국인의 교정환자로부터 새로운 생물형의 Streptococcus mutans 분리

Abstract

Isolation of a new biotype of Streptococcus mutans in Korean orthodontic patients

Jeong, Dong Ki, D.D.S., M.S.D. Advisor : Prof. Kim, Kwang-Won, D.D.S., M.S.D., Ph. D. Department of Dentistry, Graduate School of Chosun University

The 8 clinical strains of S. mutans were identified using a polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method based on dextranase gene. The aim of this study was to confirm the identification of the S. mutans strains using a 16S ribosomal RNA coding gene (16S rDNA) cloning and sequencing method, and to characterize the strains using biochemical and antibiotic susceptibility tests. The 16S rDNAs were amplified from the each of the clinical isolates by PCR using the universal primers for the bacteria. The amplicons were directly ligated with the pGEM-T easy vector. The insert DNA was sequenced using the dideoxy chain termination method. The biotype of the clinical isolates of S. mutans was determined by their ability to ferment 4 carbohydrates (mannitol, sorbitol, raffinose, and melibiose) and to deaminate arginine. The minimal inhibitory concentration for seven antibiotics against the clinical isolates of S. mutans was measured by a broth dilution assay. The results showed that the similarity of the nucleotide sequences from all of the clinical isolates was > 99% compared with that from S. mutans ATCC 25175T. Six out of the 8 strains was biotype Ⅳ [Man(+), Sor(+), Raf(-), Mel(-), and Arg(-)] such as S. sobrinus. The remaining 2 strains of S. mutans did not coincide with the general biotype of mutans streptococci. The 2 strains have the ability to ferment mannitol and sorbitol and to deaminate arginine. To our knowledge, this is a new biotype [Man(+), Sor(+), Raf(-), Mel(-), and Arg(+)], in which the two strains were named biotype VII. The susceptibility of these the 8 S. mutans strains to 7 antibiotics varied according to the strain. This indicates that the clinical isolates of S. mutans isolated from Korean subjects are similar to the type strain at the genetic level but there was some difference in the phenotype.