The family Streptococcaceae is divided into five genera in Bergey's Manual (1974): Streptococcus, Leuconostoc, Pediococcus, Aerococcus and Gemella. The genus Streptococcus is a relatively large group of organisms. They are spherical microorganisms, characteristically arranged in chains and distributed in nature. Some are members of normal human and animal flora, and others are responsible for a variety of diseases of man, animals and fish, and some are saprophytes found in milk and dairy products. Three general criteria, haemolysis, antigenic structure and biochemical characteristics are useful in identification and classification of streptococci. The API 20 STREP system was applied and evaluated for the identification of streptococci isolated from diseased fish and stoc strains. By this system, stoc strains were identified, but clinical isolates remained unidentified.
Since the first report of occurrence in 1974, streptococcal infection in cultured yellowtail Seriola quinqueradiata have been spread in almost all area in Japan increasing economical loss year by year. To establish principles for prevention and therapeutical treatment it is necessary to have sufficient informations on characteristics of the pathogen. In this paper, growth properties, survivability in seawater, distributions in culturing area and in the fish body and effects of toxins produced by Streptococcus on the infection are described. In cultural conditions, growth occurred at a range (optimum) of 10-45°C (20-37°C), 0-7.0% (0%) of NaCl concentration and pH 3.5-10.0 (7.6). Prolonged survivability was observed in seawater especially in the seawater obtained from pen-culturing area resulting for 42 days at 25°C. Pathogenic Streptococcus was detected in seawater, bottom mud and the intestine of fish such as chub mackerel Scomber japonicus and black scraper Navodon modestus. Isolation could be easily performed from the kidney, the spleen and the intestine of the infected fish. From the reason that a large number of cells were detected in the intestine of moribund fish, this organ was considered to be the principal site for the progress of the infection. Endotoxin produced by Streptococcus showed lethal activity at a level that LD50 was 32 mg/10 g body weight of fish. Though exotoxin also produced by Streptococcus had relatively low lethal activity that LD50 was 79 mg/10 g, it was considered to have a supporting function to progress the disease.
The comparison of the cultural, biochemical and serological properties of 286 strains of Streptococcus sp. isolated from streptococcal disease of cultured yellowtail (Seriola quinqueradiata) at various parts of Japan during the period from 1974 to 1980 were investigated. It was confirmed that these strains have been possessed a very similar characteristics according to the cultural and biochemical tests. Although some cultural characteristics of Str. sp. are most similar to those of Str. faecalis and Str. faecium, Str. sp. are not react with group D streptococcus antiserum. Therefore, it is necessary to establish the idetification method for Str. sp. Str. sp. were presumptively identified by bile-esculin medium (growth in 40% bile and hydrolyze esculin), eosin-methylen blue medium (no ferment lactose), a modified NaCl medium by QADRI (nochange color) and the rapid hippurate hydrolysis test by HWANG (negative reaction), and in addition, accurately identified by the slide agglutination using Str. sp. antiserum prepared with Str. sp. KGtype strain. Besides, Str. sp. could be detected in pur and a high frequency from brain rather than other organs of diseased fish in our own past experience.
The present author has been performed isolation of Streptococcus sp. from the brain of diseased yellowtail (Seriola quinqueradiata) since January in 1979. This method has been useful to readily diagnose Streptococcus infection of fish with some pathological symptoms as exophthalmos, protrusive lesions on the inside surface of the opercle and the caudal peduncle, and epicarditis. Moreover, this method was confirmed to be applicable to infected fish which did not yet exhibit any pathological symptoms because of pure and sure isolation. This paper describes the results of the study on the bacterial isolation with the above mentioned method in 1979 and 1980.
Recently, streptococcal infections have been frequently observed in freshwater fishes, especially in ayu, Plecoglossus altivelis, cultured in Tokushima Prefecture, Japan. The first outbreak was observed in 1977. Since then, the epizootics have occured among ayu in the summer and autumn every year, and caused sereious economic losses. The present paper deals with occurrence, diagnostics and clinical studies of the disease.
The present author histopathologically studied on various Streptococcicoses : 1) infections with a-hemolytic bacteria in sea-cultured yellowtail (Seriola quinqueradiata), striped beakperch (Oplegnathus fasciatus), Japanese horse mackerel (Trachurus japonica) and striped jack (Caranx delicatissimus), 2) infections with β-hemolytic bacteria in sea-cultured Japanese flounder (Paralichthys olivaceus), ayu (Plecoglossus altivelis) and rainbow trout (Salmo gairdneri) which were reared in fresh-water ponds. The bacteria frequently infected eyes of fishes. Histopathologically α-hemolytic bacteria usually caused granulomatous inflammation at infected lesions of yellowtail, striped beakperch, Japanese horse mackerel and striped jack. β-hemolytic bacteria caused systemic infection with septicemia in ayu and rainbow trout, and extensive suppurative inflammation in eyes of Japanese flounder.
This station has been investigating race of sea-cultured fishes, amount of the production, number of fish-culturist, occurrence of diseases and amount of loss of the fish due to diseases in Mie Prefecture since 1960. And, the author has concentrated on investigation into Streptococcicosis of yellowtail (Seriola quinqueradiata) and other sea-cultured fishes because of causing great amount of loss since 1975. This paper is describing the results of the investigation from 1960 through 1981 and author's opinion on prophylaxis and treatment for Streptococcicosis of yellowtail.
The relation between the streptococcicosis and the food quality was ascertained by our epidemiological reserch. The food species, quality and the way of melting for frozen food were considered to be very important promoting factors of the disease. The methods for the preventions against the disease were proposed based on a few experiments as follows: 1. It was supposed that the cultured fishes were infected oraly through foods which were polluted by the pathogenic bacteria. To prevent the pollution by pathogen and it's growth, 1) washing and melting food fish by clean water, 2) feeding frozen food without melting and 3) feeding processed food (pellet) were proposed. 2. It was also clarified that the deteriolated food and unbalanced nutrition were not good in maintaining the resistancy of fishes against the disease. Inorder to maintain the food quality and nutritional balance, unmelted food and vitamin mixture were used and then it was observed that the resistancy of host was remarkably increased. 3. The resistancy of host was also influenced by organic pollution of water so that the water quality must be maintained in good condition. It is relatively difficult to recover yellowtail from the streptococcicosis by drags, but the preventions above mentioned are effective in early stage of disease in population level, so that the early detection and diagnosis of the disease in the fish farm is especially important. In Kochi Prefecture, the improvement of culture equipment and hygienic education have been tried among the farmer of yellowtail culture.
Mortality caused by the streptococcal disease of cultured yellowtail at fish farms in Kitaura Bay, Miyazaki Prefecture was investigated. The results obtained were as follows : 1) It has been found that a severe damage of the streptococcal disease of cultured yellowtail occurred at central areas in the fish farms. 2) It was demonstrated that a change of damage the streptococcal disease of cultured yellowtail has been closely related to a fluctuation of a haul catch of a sardine which are using as the feed of cultured yellowtail. From above mentioned results, it was concluded that an occurrence of the streptococcal disease of cultured yellowtail has been originally caused on the fish culturing technique.
The results of the basic and application studies with doxycycline (DOTC) were summarized as follows. Doxycycline was stable in both substance and preparation. It also keeps its stability in feed for yellow-tail. The half life of doxycycline was 7 days in sea-water or in sea-water and active sludge. Doxycycline had very low toxicity against experiment animals and yellow-tail: its safety was high. It was quickly absorbed in body of experiment animals and was distributed systemically. Doxycycline was efficacious against Streptococcosis in yellow-tail at the administration of 20-50 mg/kg of body weight. Its withdrawal period was 20 days.
Application of erythromycin (EM) to spontaneous streptococcal infections in cultured yellowtails, Seriola quinqueradiata, were reviewed. In vitro, EM was active against a wide range of bacteria pathogenic for fish. Stock strains and fresh field isolates of Streptococcus sp. were susceptible to EM whose MIC values varied from 0.05 to 0.2μg/ml. There were no resistant streptococcal strains so far tested. The MIC of EM was slightly affected by inoculum size and medium pH. In vivo, orally administered EM was effective against experimental infections with Streptococcus sp. in yellowtails. It was easily absorbed by oral administration and distributed to blood and tissues including brain within 1 h after administration. Peak levels were usually attained 1 to 3 h postadministration. Acute toxicity of EM was low in yellowtails, its LD50 value being more than 2, 000mg/kg. Abnormality possibly caused by EM was not found in yellowtails receiving the repeated doses of the drug at a dose of 100 mg/kg/day for 10 days. In the clinical studies, EM was effective against streptococcal infections in cultured yellowtails at doses of 25-50 mg/kg/day for 4-7 days.
Spiramycin for fishery drugs had the governmental approval for production and was introduced to the market in 1981. This paper deals with general properties and various experimental data of spiramycin embonate concerning physicochemistry, stability, anti-bacterial activities, general pharmacology, absorption, excretion, toxicity, safety, residue and clinical studies.