The cell-surface properties of strains of Lactococcus garvieae were examined. Two capsular types were found, one with a highly developed capsule (KG9408) and one with a micro-capsule (MS93003) carrying fimbriae-like components projecting from the cell surface. One strain (NSS9310) had neither cell capsular nor fimbriae-like structures on its cell surface. The strains with the highly developed capsule were more virulent to fish than either the micro-capsular or non-capsular strains. The KG9408, MS93003 and NSS9310 strains could be clearly differentiated by their susceptibility to bacteriophages. Protection against L. garvieae infection was induced in the yellowtail Seriola quinqueradiata by immunization with formalin-killed L. garvieae KG9408 and MS93003 cells. Although protection was also induced by immunization with NSS9310, the level of protection was significantly lower than that with KG9408 and MS93003 vaccines. Passive immunization with yellowtail immune sera raised against KG9408 and MS93003 conferred strong protection on yellowtail with rapid bacterial clearance after challenge with L. garvieae. Immunoblotting analysis of protein antigens extracted from L. garvieae strains using rabbit anti-KG9408 and anti-MS93003 sera and yellowtail anti-KG9408 and anti-MS93003 sera indicated that some bands in KG9408 and MS93003 strains were not detectable in NSS9310.KEY WORDS: Immunogenicity ⋅ Lactococcus garvieae ⋅ Seriola quinqueradiata ⋅ Cell capsule ⋅ Fimbriae Resale or republication not permitted without written consent of the publisherDis Aquat Org 51: [169][170][171][172][173][174][175][176][177] 2002 thought to play roles in the pathogenicity of L. garvieae infection, possibly by increasing resistance to fish phagocytosis (Yoshida et al. 1996(Yoshida et al. , 1997.Control of Lactococcus garvieae infection in yellowtail culture has depended on chemotherapy with macrolides. The identification of multiple drug-resistant strains has indicated future problems in controlling the pathogen (Aoki et al. 1990). Recently, oral and injectable vaccines against L. garvieae infection in Seriola quinqueradiata have been developed and commercialized in Japan. Experimental vaccination against L. garvieae has been described (Iida et al. 1982, Sato et al. 1996 and has been reported to provide immunity and increased opsonic activity in the fish. However, no detailed information on the antigenicity of L. garvieae phenotypes nor the duration of the immunity was given. The protective mechanisms of the L. garvieae vaccine remains unknown.In a previous study, Ooyama et al. (1999) reported that formalin-killed Lactococcus garvieae KG-phenotype (capsulated phenotypes) cells and KG+ phenotype (noncapsulated) cells induced strong immunity in Seriola quinqueradiata against artificial infection and longlasting agglutinating titres against non-capsulated cells (avirulent KG+ phenotype). Furthermore, appendages (fimbriae-like structures) were seen extending from the cell surface of L. garvieae KG-phenotype, with some destruction of...

Yellowtail Seriola quinqueradiata were immunized with 2 different Lactococcus garvieae bacterin, formalin-killed KG-phenotype cells (capsulated phenotype) and formalin-killed KG+ phenotype cells (unencapsulated phenotype). These 2 injected vaccines conferred long-term protection to yellowtail against an artificial infection of an encapsulated Lactococcus garvieae strain with long-lasting agglutinating titres against KG+ phenotype cells. However, no agglutinating titres or low agglutinating titres against KG-phenotype cells were detected in fish given each of these bacterin. These results suggested that a capsule in KG-phenotype cells apparently affects their immunogenicity, but the antlgens which conferred protection to fish against lactococcal infection may be located on the surface of KG+ phenotype cells, and are not cell capsules in KG-phenotype cells. The protection offered by a formalin-killed KG+ phenotype cell vaccine would not appear to be strain specific. Encapsulated L. garvieae cells were well phagocytosed, and fimbrie-like appendages were seen in KG-phenotype cells after treatment with yellowtail immune serum.

ABSTRACT--Experimental transmission of Myxidium fugu and Myxidium sp. TP (formerly de scribed as Myxidium sp. in tiger puffer Takifugu rubripes) among tiger puffer was successful by the following 3 methods; 1) feeding infected gut tissue, 2) cohabitation with infected fish, 3) expo sure to effluent from a tank containing infected fish. Regardless of the transmission methods, prevalences of infection in the intestine with M. fugu reached 100%. However, those with Myxidium sp. TP, which is suspected of an etiological agent of the emaciation disease, varied among experiments conducted in different months, suggesting that development of Myxidium sp. TP was strongly influenced by the ambient temperature.It was evident that trophozoites of Myxidium sp. TP excreted from the infected fish were transmittable directly to other fish. Mortalities and morbidities in fish experimentally infected with Myxidium sp. TP seemed to be asso ciated with the parasite's development which might be promoted by higher temperature. The present study suggests that fish-to-fish transmission of Myxidium spp. occurs in sea cages, induc ing a rapid spread of the emaciation disease among farmed tiger puffer.

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A method for the diagnosis of nocardiosis in yellowtail (Seriola quinqueradiata), using polymerase chain reaction (PCR), was developed in this study. Primers specific for Nocardia seriolae were synthesized based on the alignment of 16SÀ23S rRNA internal transcribed spacer region sequences of N. seriolae. The primers did not amplify specific PCR product from other fish pathogens. However, two and three fishes could be diagnosed as infected with N. seriolae by clinical signs and bacterial isolation. PCR amplification of N. seriolae by specific primers detected six infected fishes. Thus, the primers used in this study are useful in detecting nocardiosis in fish.