ブリのStreptococcus iniae感染症に関する研究

佐古, 浩

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ブリのStreptococcus iniae感染症に関する研究

https://fra.repo.nii.ac.jp/records/2003177

Item type

紀要論文 / Departmental Bulletin Paper(1)

公開日

2024-04-25

タイトル

ブリのStreptococcus iniae感染症に関する研究

言語

タイトル

Studies on Streptococcus iniae Infection in Yellowtail, Seriola quinqueradiata

言語

jpn

キーワード

言語

主題Scheme

Other

主題

streptococcicosis; Streptococcus iniae; yellowtail; vertebral deformity; pathogenicity; vaccination; chemotherapy

資源タイプ

資源タイプ識別子

http://purl.org/coar/resource_type/c_6501

資源タイプ

departmental bulletin paper

アクセス権

metadata only access

アクセス権URI

http://purl.org/coar/access_right/c_14cb

著者

佐古, 浩

抄録

内容記述タイプ

Abstract

内容記述

Streptococcicosis caused by ß-hemolytic Streptococcus (BHS) is one of the serious invasive diseases in cultured yellowtail, Seriola quinqueradiata in Japan. BHS is distributed not only in cultured yellowtail but also in many other marine and freshwater fishes. Prevention of this disease is important for the successful culture of yellowtail. The present study was performed on BHS infection in cultured yellowtail to investigate the occurrence, etiology, and taxonomy and pathogenicity of the causative bacterium. For the purpose of establishing control measures against this disease, prophylaxis and treatment of the disease were also studied. A BHS was frequently isolated from the brain of cultured yellowtail juveniles showing vertebral deformity. Morbidities were 10 to 20% in the case examined. A BHS was also isolated from deformed wild yellowtail and common mackerel, Scomber japonicus. Results of these surveys suggested that BHS is related to vertebral deformity of yellowtail and distributed also in other cultured and wild fishes. Comparative taxonomical studies were performed over a total of 14 BHS strains isolated from diseased cultured yellowtail, Japanese flounder, Paralichthys olivaceus, ayu, Plecoglossus altivelis, and wild common mackerel, with strains of Streptococcus iniae ATCC 29178, ATCC 29177 and S. equisimilis IID 681. The phenotypic properties of the fish isolates well agreed with each other, and were identical to those of S. iniae ATCC 29178, which was isolated from Amazon freshwater dolphin, Inia geoffrensis. The surface antigens of the S. iniae isolates from different sources of fish were shown to be serologically homologous, whereas the serotype of the fish isolates was different from that of S. iniae ATCC 29178. Occasional death was observed with S. iniae isolates although it frequently caused vertebral deformity to yellowtail by artificial infection through various challenge routes. Clinical symptoms such as exophthalmos, corneal opacity, epicarditis, and congestion on the inside of the opercula and uper jaw were observed in artificially infected yellowtail. Sensitivity to S. iniae infection decreased with the increase of body weight. All the strains isolated from cultured marine and freshwater fish, and wild fish possessed the same pathogenicity to yellowtail and ayu. These results indicate that the distribution of BHS in marine and freshwater environment is ubiquitous and they are the same strains as S. iniae. Considering the salt tolerance of S. iniae, reported, S. iniae might have originated from terrestrial animals. Viable counts of S. iniae in the brain of yellowtail inoculated with the bacteria increased faster and period required for the occurrence of vertebral deformity after the inoculation of bacteria became shorter as the water temperature increased at 18-30°C. The fate of S. iniae in various organs of yellowtail after experimental infection indicates that the growth of the bacteria and subsequent infection in the brain is the cause of the occurrrence of vertebral deformity. S. iniae isolated from yellowtail have been confirmed to be pathogenic to mice by intraperitoneal injection. Immunity of yellowtail recovered from experimental infection with S. iniae was examined to know the efficacy of vaccination as a possible way of prevention. The agglutinating antibody titers in the sera isolated from recovered fish against the S. iniae were 1:4-1:16. After reinfecting the recovered fish, no clear symptom was observed, furthermore number of viable bacteria in the blood, spleen, and kidney were decreased faster than those of the control fish. Moreover, increase in viable bacterial cell number was not observed in the brain of the recovered fish. Results of this experiment indicate that fish recovered from S. iniae infection acquired resistance to subsequent reinfection. To know the efficacy of vaccination, formalin killed cells (FKC) of S. iniae were administered to yellowtail fingerling by immersion, oral, and intraperitoneal injection methods. Twenty and 35 days after vaccination, each group was challenged by intraperitoneal inoculation of the bacteria. At this time, agglutinating antibody titers were undetectable (< 1:2) in the sera of fishes vaccinated by immersion and oral methods, whereas in those vaccinated by injection the titers were barely detectable (< 1:2-1:8). After the challenge, fishes vaccinated by injection showed neither clinical signs of the disease nor they died. Furthermore, bacterial cell numbers decreased rapidly in the blood, spleen, and kidney whereas the numbers remained static in the brain. On the other hand immersion and oral vaccination were ineffective, showing typical clinical signs of the disease. Results of this experiment indicate that vaccination by injection method is the best among three different administration routes in preventing S. iniae infection in cultured yellowtail. Passive immunization using the sera isolated from the fish recovered from S. iniae infection and the fish immunized with FKC of S. iniae were also effective in preventing to S. iniae infection. The in vitro activities of 36 antimicrobial agents were tested against 15 strains of S. iniae isolated from diseased fishes by the standard agar plate dilution method. Penicillins, cephalosporines, macrolides, tetracyclines, rifampicin, lincomycin, sodium nifurstyrenate, and diaminopyrimidines were highly effective (MIC, 0.00313-0.78 μg/ml) against all the strains tested. Chloramphenicols and bacitracin were also effctive (MIC, 0.78-3.13 μg/ml). Susceptibility of S. iniae to penicillins, cephalosporines, rifampicin, bacitracin, sodium nifurstyrenate, and diaminopyrimidines was higher than that of Enterococcus seriolicida. In vivo therapeutic effects of selected 12 drugs, to which S. iniae is highly susceptible, were also observed in experimentally infected yellowtail. Among the 12 selected drugs, penicillins, macrolides, tetracyclines, rifampicin, lincomycin and sodium nifurstyrenate were found to be effective against S. iniae infection.

言語

書誌情報

ja : 南西海区水産研究所研究報告
en : Bulletin of Nansei National Fisheries Research Instituite

巻 31, p. 63-120, ページ数 58, 発行日 1998-03

出版者

南西海区水産研究所

言語

出版者

Nansei National Fisheries Research Instituite

言語

ISSN

収録物識別子タイプ

PISSN

収録物識別子

0388-841X

書誌レコードID

収録物識別子タイプ

NCID

収録物識別子

AN00181988

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