Analysis of the Prevalence of Tetracycline Resistance Genes in Clinical Isolates ofEnterococcus faecalisandEnterococcus faeciumin a Japanese Hospital

Prevalence of seven tetracycline resistance (TCR) genes—tet(L), tet(M), tet(K), tet(O), tet(S), tet(T), and tet(U)— which are known to be distributed to gram-positive cocci was analyzed for 224 Enterococcus faecalis and 46 Enterococcus faecium clinical isolates obtained in a Japanese hospital. Any of the TCR genes was detected in 75.9% of all the enterococcal strains. The tet(M) was detected at highest rates in both E. faecalis (75.0%) and E. faecium (69.6%), followed by tet(L), which was harbored in 6.7% of E. faecalis isolates and 30.4% of E. faecium isolates. The tet(O), tet(S), and tet(T) were detected in E. faecalis at low frequencies mostly associated with tet(M), while tet(K) and tet(U) were not detected. Nucleotide sequences of tet(S) from E. faecalis strains were identical to that reported in Listeria monocytogenes. Sequences of tet(O) from two E. faecalis strains were almost identical to each other and also to those from Streptococcus pneumoniae, Streptococcus pyogenes, Streptococcus mutans, Campylobacter jejuni, and Campylobacter coli, although minor sequence divergence was observed. The tet(T), which had been reported only in Streptococcus pyogenes, was found in five E. faecalis strains. Sequence of the enterococcal tet(T) differed from that of S. pyogenes by only four nucleotides (four amino acids) and showed high sequence identity (99.8%, amino acid level). Enterococcal strains with any one TCR gene or those with two TCR genes showed generally similar MICs of tetracyclines, and no evident difference in resistance level was observed.