Drug resistance in a non-hemolytic Streptococcus sp. isolated from cultured yeltowtail Seriola quinqueradiata

The antibacterial activities of 19 chemotherapeutic agents were tested against 370 strains of a non-hemolytic Streptococcus sp.pathogenic for a marine fish, the yellowtail Seriola quinqueradiata.The strains were isolated from cultured yellowtail in 1986 and 1987.Sixty-two of the tested strains showed resistance to macrolide antibiotics (MLs), lincomycin (LIM), tetracycline (TC), and chloramphenicol (CP).These resistant strains were classified into intermediate-and high-level resistance to MLs, LIM, TC, or CP.Intermediate-level resistance was constitutive and the responsible resistance determinants were not transferred to S, faecalis JH2-2 or to Streptococcus sp.SSS-1, the latter a yellowtail isolate.On the other hand, hgh-level resistance to MLs, LIM, and TC and to MLs, LIM, and CP was inducible and transferable to S. faecalis JH2-2 and to Streptococcus sp.SSS-1.These drugresistant strains of the non-hemolytic Streptococcus sp., capable of transferring their resistance, were first isolated in cultured yellowtail in various areas of Japan.