ヒラメのβ溶血性レンサ球菌症に対するファージ治療試験

Abstract

We examined the therapeutic effect of Streptococcus iniae phages isolated from fish culture environments against experimental streptococcicosis of Japanese flounder Paralichthys olivaceus. Phage sensitivity tests with a double agar method revealed that 31 of 35 S. iniae strains from the flounder have a similar sensitivity to six phage isolates. In phage therapy experiments, fish were injected intraperitoneally (IP) with S. iniae PSi402 and 1 h later IP-injected with a mixture of two or four phage isolates, and observed at 25 degrees C for 2 wk. Mortalities of fish receiving phages were significantly lower than those of control fish without phage-treatment in all four trials. The effect of phage treatment was also demonstrated even at 24 h post-infection, when cell numbers of S. iniae were 10(7.4) and 10(4.5) CFU/g in the kidneys and brains of fish, respectively. However, as phage-resistant S. iniae were frequently isolated from dead fish in the phage-treated group, further investigations are required to establish phage therapy of the disease.