Antibacterial action of chemotherapeutic agents against non-hemolytic Streptococcus sp. isolated from cultured marine fish, yellowtail Seriola quinqueradiata.

Abstract

The susceptibility of various chemotherapeutic agents against five hundred and sixty one strains of non-hemolytic Streptococcus sp. were tested. These strains were collected from streptococcal infection of marine fish, yellowtail Seriola quinqueradiata, from 1974 to 1981 in various districts of Japan. The fifteen kinds of chemotherapeutics used were ampicillin (ABP), cephalexin (CEX), cephazoline (CEZ), chloramphenicol (CM), tetracycline, streptomycin (SM), kanamycin (KM), erythromycin (EM), leucomycin (LM), josamycin (JM), triacetyloleandomycin (TAO), lincomycin (LIM), nalidixic acid (NA), furazolidone (NF), and sulfamonomethoxine (SA). Four hundred and eleven strains isolated from 1978 to 1981 were additionally tested for sensitivity to doxycycline, trimethoprim (TMP), and ormethoprim (OMP), and one hundred and fifty nine strains isolated in 1981 were also tested for sensitivity to spiramycin (SP). EM was the most effective against the strains among the tested drugs, with all strains inhibited at a concentration of 0.1μg/ml or less. Successively, ABP, tetracycline derivatives, JM, TAO, and LIM had high antibacterial activity, and their MIC values for 90% of the strains were 1.24μg/ml or less. These strains were sensitive to CM, CEZ, KM, and SP, and moderately sensitive to CEX, SM, NF, TMP, and OMP. The strains of Streptococcus sp. were intrinsically resistant to NA and SA. Key words: yellowtail, fish disease, fish-pathogenic bacteria, streptococcal infection, non-hemolytic Streptococcus sp., drug susceptibility.