Incidence of Tetracycline Resistance Genes, tet(M) and tet(O), in Streptococci Isolated from Dental Plaques of Koreans

Streptococci are among the normal human microflora thatpopulate the oral cavity. However, oral streptococci are knownas a major causative agent for dental caries and bacterialendocarditis. Tetracycline is a broad-spectrum antibiotic thatis used for oral infections but two mechanisms of tetracyclineresistance in streptococci have been reported. The tet(K) andtet(L) genes in these bacteria are related to the active efflux oftetracycline, whereas tet(M) and tet(O) confer ribosomalprotection from this antibiotic. It has been reported that thetetracycline resistance of streptococci is related mainly to theactivity of tet(M) and tet(O). In our present study, we examinedthe prevalence of tet(M) and tet(O) in oral streptococci isolatedfrom Korean dental plaques using PCR. One hundred and fortyeight of 635 isolates (23.3%) were tetracycline resistant; 68 ofthese strains (46%) harbored tet(M) and 3 strains (2%) werepositive for tet(O). However, tet(M) and tet(O) did not co-existin any of the resistant strains. Seventy seven of the 148tetracycline resistant strains (52%) were negative for both thetet(M) and tet(O) genes.