Oral Biol Res.  2021 Jun;45(2):75-81. 10.21851/obr.45.02.202106.75.

Genetic diversity of the tet(M) gene in tetracycline-resistant oral streptococci

• Jeong D
• Lee SY

• KMID: 2517483
• DOI: http://doi.org/10.21851/obr.45.02.202106.75

Abstract

Tetracycline resistance occurs at a high frequency among clinical isolates of both gram-positive and gram-negative bacteria. The mechanism and genetics of tetracycline resistance have not been extensively studied in streptococci, although the overwhelming majority of clinical isolates are tetracycline resistant. tet(M) is the most common tetracycline-resistance gene in streptococci. The aim of this study was to examine the genetic diversity of tet(M) genes in tetracycline-resistant oral streptococci from dental plaque. Streptococci were isolated from supragingival plaque samples of healthy persons. The isolates were then identified at the species level, and the minimum inhibitory concentration (MIC) of tetracycline was determined. Genomic DNA was extracted from tetracyclineresistant isolates and tet(M) was amplified using polymerase chain reaction with tet(M)-specific primers. The polymerase chain reaction products were cloned, DNA sequencing was performed, and the sequences were compared using an alignment program. The estimated nucleotide divergence between different tet(M) alleles ranged from 0.00% to 6.07% among oral streptococci. The tet(M) genes from oral streptococci consisted of regions similar in sequence, interspersed with regions that differed at some nucleotide sites, revealing a mosaic structure. The percent nucleotide divergence of tet(M) was unrelated to the MIC values of tetracycline for oral streptococci, and bacterial strains in the same streptococcal species showed different heterogeneity in tet(M). The divergences of tet(M) nucleotide sequences among oral streptococci were comparable with those of other bacterial genera. Our findings may provide basic information about the transposition processes associated with tet(M) in oral streptococci.

Keyword

Diversity; Resistance; Sequence; Streptococci; Tetracycline