DAO prepress abstract  -  DOI: https://doi.org/10.3354/dao03212

Host range and influence of a cell capsule on the phage efficacy of three Lactococcus garvieae lytic phages

Truong Dinh Hoai, Issei Nishiki*, Terutoyo Yoshida, Toshihiro Nakai

*Email: nishikii@affrc.go.jp

ABSTRACT: Three lytic phages (PLgW-1, PLgY-16 and PLgY-30) were previously used for phage-typing Lactococcus garvieae, a bacterial pathogen of various marine fish species, and were demonstrated to be potential therapeutants for infections caused by L. garvieae. The morphology, host range and efficacy of these phages have not been investigated in detail, however. The current study examined the lysis spectrum of these 3 phages against 16 different genotypes of L. garvieae and the influence of a bacterial capsule on phage efficacy, to aid in developing an effective treatment for lactococcosis in fish. Morphological analysis by transmission electron microcopy revealed that all three phages belonged to the family Siphoviridae and had a minor difference in morphology. These phages lysed a high proportion of their bacterial host (93.7% of the different L. garvieae genotypes). In addition, the efficacy of the plating assays was affected by both the phages and their bacterial host, in which phage efficacy was obviously affected by the bacterial capsule. The results of this study may be useful for developing appropriate strategies to use these phages to control various genotypes of L. garvieae causing disease in marine fish.