Antimicrobial susceptibility of
Streptococcus parauberis against nine drugs were investigated in 64 strains isolated from Japanese flounder
Paralichthys olivaceus at different culture areas of western Japan, and resistance genes were determined by PCR and Southern blot hybridization. Five of the tested strains belonging to
S. parauberis serotype I (44 strains) were resistant to oxytetracycline and erythromycin and were found to possess both
tet(S) and
erm(B) genes. Minimum inhibitory concentrations (MICs) of oxytetracycline and erythromycin were 128 and 512
μg/mL, respectively. Southern blot hybridization analysis showed that the
tet(S) gene was encoded on an 11-kb conjugative plasmid, while the
erm(B) gene resided on the chromosomal DNA. All of the examined
S. parauberis serotype II strains (20 strains) were tetracycline-resistant (MIC = 32
μg/mL) and were found to possess
tet(M) gene. Both
int (integrase) and
xis (excisase) genes were also detected in all of the serotype II strains, suggesting the presence of Tn
916-related element in these strains. These results present a threat of difficulty in treatment of
S. parauberis infection by tetracyclines, especially those caused by serotype II strains.
抄録全体を表示