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Immunomodulatory effects of immunoactive peptides from the fermented products of chicken egg (EF203) administered orally to rainbow trout, Oncorhynchus mykiss , were investigated. The chemiluminescent responses of kidney phagocytes after treatment with EF203 were significantly increased. Fish administered EF203 showed high phagocytic activities as compared to controls, and immunomodulatory effects were found to be dose dependent. Fish treated with EF203 displayed an increased resistance to both natural and experimental beta-haemolytic streptococcal infection.

The present paper describes a herpes-like virus, tentatively designated as EHVF (Eel Herpesvirus in Formosa), isolated from diseased Japanese eels (Anguilla japonica Temminck & Schlegel) in Taiwan.This virus had DNA as its nucleic acid, sensitive to ether and chloroform, and resistant to freezing and thawing treatments. Enveloped mature viral particle measured 200 nm in diameter with nucleocapsid of 120 nm.The virus successfully replicated in CCF, CCT, TO-2, BGK, DK-1 and EO-2 cell lines at temperatures from 15°C to 33°C (optimal temperature 24°C). When these cells were infected with EHVF, syncytium formations were observed in CCF, CCT, TO-2, BGK, EK-1 and EO-2 cell lines. However, HeLa, Vero, L, AF, AK, BF-2, CCG, CCO, CF, CHH-1, CHSE-214, EPC, FHM, FS, JF, LF, MH and RTG-2 cell lines were refractory to the multiplication of this virus.No mortalities were observed among eels injected with EHVF, but the virus was reisolated from the kidneys and livers of infected eels 60 days after injection. On the other hand, carp injected with EHVF showed 37% mortality during 60 days and the virus was reisolated from all the dead fish and 84% of the survivors.

In vitro antimicrobial activity of bicozamycin (BCM), a cell wall synthesis inhibitor, was investigated against Pasteurella piscicida. Minimum inhibitory concentrations (MIC) of BCM against 263 clinical isolates of P. piscicida ranged from 1.56 to 6.25μg/ml. High incidence of drug-resistant strains agains other drugs such as β-lactamam antibiotics and pyridonecarboxylic acids were recognized. No cross resistance between BCM and other antibacterial agents were observed. BCM displayed bactericidal activity at its MIC level.P.piscicida strains showed a slowly increasing and stepwise pattern of artificial developmen of resistance against BCM.From the results obtained, it may be suggested that BCM would be applied as a new type of therapeutic agent among the cell wall synthesis inhibitors for the treatment of pseudotuberculosis.

Effects of various concentrations of specific immune serum on phagocytosis and phagocytosisassociated chemiluminescent (CL) responses were investigated with sheep red blood cells (SRBC) and rainbow trout (Oncorhynchus mykiss) phagocytic cells. When heat-inactivated rainbow trout anti-SRBC serum was used to opsonize SRBC, rates of phagocytic ingestion of SRBC by phagocytes increased with lower dilutions of the antiserum, and CL activities also rose with lower dilutions of the antiserum. The number of phagocytized SRBC per phagocyte increased in response to concentrations of the antiserum. These results indicate that CL response correlates with phagocytosis of which the activity depends on the concentration of specific immune serum used as an opsonin.

The spontaneous rosette formation of peripheral leucocytes of carp with red blood cells of various mammals was investigated. Spontaneous rosette formation was observed with SRBCs, HRBCs and BRBCs with the frequency of rosette formation being higher with SRBCs and HRBCs than with BRBCs. Variations in surface morphology, in cell size of the rosette forming cells and in rosette formations were observed under light and scanning electron microscope. However, by examining Giemsa-stained preparates, the RFCs were identified as lymphocytes. The spontaneous rosette formation occurred gradually depend-ing on the incubation time. The spontaneous rosette formation was not specific to SRBCs and was observed at a temperature range of 0°C to 37°C. In these respects the rosette formation of carp lymphocytes differed from the earlier reported rosette formation of mam-malian lymphocytes.

Two hundred fifty nine strains of Vibrio anguillarum were isolated from cultured ayu of various districts in Japan from 1974 to 1977. These strains were tested for their susceptibility to 6 chemotherapeutic agents : sulfamonomethoxine, chloramphenicol, tetracycline, nalidixic acid, nitrofurazone and trimethoprim. Nine of the 259 strains were sensitive to all drugs tested. The remaing 250 strains were resistant to various combinations of the six drugs tested. Transferable R plasmids were detected in 165 out of the 250 resistant strains, and strains from all districts turned out to have some transferable R plasmids. This high incidence of drug resistant strains of V. anguillarum was assumed to be due to the selective pressure exerted by chemotherapeutic agents used during culturing the fish. These strains fall into at least three different O sero-groups.The efficacy of hyperosmotic infiltration technique (HI) in controlling vibriosis of ayu was tested. Experimental fish were first placed in a solution containing 5.32% NaCl for 2 min. and then placed in a vaccine solution of V. anguillarum (5.0 × 108/ml) bacterin for 3 min. A month after immunization, the immunized fish were found to be resistant to V. anguillarum to intraperitoneally injected.In the second experiment, formalin-added culture of V. anguillarum was centrifuged and the precipitated bacterial cells were resuspended in saline solution of the same volume as the original culture. As in the first experiment, the fish were held in a solution of 5.32% NaCl for 2 min, and then placed either in the above suspension or the medium supernatetant for 3 min. Immersion of fish in the suspension provided adequate protection but immersion of fish in the supernatant was not effective to protect against intraperitoneally injected V. anguillarum a month after vaccination. Treatment with the supernatant caused high mortality to ayu presumably due to the exotoxin from bacteria but immersion in the Vibrio cell suspension did not cause higher mortality than a control group immersed only in 5.32% NaCl solution during are one month.In the third experiment, the fish were immersed in 5.32% NaCl solution containing lyophilized whole cells of V. anguillarum for 3 min. The vaccinated fish turned out to be well protected against V. anguillarum intraperitoneally injected a month after treatment. The HI method could be used most effectively to immunize ayu against vibriosis.

Infection with multiple drug-resistant strains of Vibrio anguillarum was observed in ayu (Plecoglossus altivelis) farms from 1981 to 1983. The strains collected from various areas of Japan showed resistance to various combinations of nine drugs : chloramphenicol (CP), tetracycline (TC), streptomycin (SM), ampicillin (ABPC), colistin, nalidixic acid, furazolidone, sulfamonomethoxine (SA), and trimethoprim (TMP). The detected R plasmids showed resistance to CP, TC, SM, ABPC, SA, and/or TMP. The digestion patterns of the R plasmids were identical. These R plasmids also showed high homology with the R plasmids detected in 1980 as determined by the Southern blot hybridization method. In other words, drug resistant strains of V. anguillarum carrying R plasmids with the same DNA structure have been distributed in ayu farms since 1980 in Japan.

養殖ニジマスのβ-溶血性 Streptococcus sp.に起因する連鎖球菌症の自然流行例についてEMによる治療効果を検討し,次のとおりの結果を得た。1.本症の流行例から分離したβ-溶血性 Streptococcus sp.菌株のEMに対するMICは0.05 μg/mlであった。2. 水産用ピマリン(大日本製薬)を50 mg(力価)/kg/日の割合で5日間投薬したところ,顕著な治療効果が認められ,観察期間中に再発はなかった。

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.

New pyridonecarboxylic acids (PCAs) were evaluated for in vitro antibacterial activity against Pasteurella piscicida, Vibrio anguillarum, Edwardsiella tarda, and Streptococcus sp., which were pathogens isolated from diseased fish in Japan. The minimal inhibitory concentrations of 11 PCAs, nalidixic acid, oxolinic acid, piromidic acid, pipemidic acid, miloxacin, flumequine, enoxacin, ofloxacin, norfloxacin, ciprofloxacin, and FR77040, were determined with the serial twofold agar dilution method. Newer PCAs, enoxacin, ofloxacin, norfloxacin, ciprofloxacin, and FR77040, showed the strongest antibacterial activity against all the fish pathogens. Oxolinic acid, miloxacin, and flumequine were highly active against the tested fish pathogens except Streptococcus sp. The remaining PCAs, nalidixic, piromidic, and pipemidic acids, were also effective against gram-negative pathogens, but the level of activity was even lower than that of the previous three. The frequency of spontaneous mutation of the pathoge...

ペニシリン系半合成抗生物質アモキシシリン(AMPC)の数種魚病細菌に対する抗菌活性を調べた。AMPCは特にPasteurella piscicidaに対して低濃度で発育を阻止した。AMPCとアンピシリン(ABPC)のP.piscicidaに対する殺菌活性を比較したところ, 同一力価においてAMPCがより強い殺菌効果を示した。また, 試験管内における耐性獲得試験において, P.piscicidaは20回継代後もAMPCに対する耐性獲得は認められず, ブリ類結節症の治療薬として期待できる成績が得られた。

Twenty different fish diets marketed in Japan were examined for the microbial flora.The total counts of aerobic bacteria determined at 30°C ranged from 1.8×103 to 8.0×105 pergram of diet with a mean value of 1.4×105. The microflora of these diets were consisted mainly of Gram-positive bacteria, and the most predominant organisms belong to the genus Bacillus and Staphylococcus. The total fungal plate counts determined at 20°C ranged from 4.0×10 to 9.6×104/g. of the diet with a mean value of 1.1×104/g. Coliform organisms were detected in 16 samples and Escherichia coli was isolated from 10 out of the 16 samples. Streptococcus were found in 4 samples. No Salmonella was detected but Vibrio was detected in 3 out of the samples. Clostridium perfringens producing lecithinase was isolated from 10 out of the 20 samples.

There was no mortality in ayu (Plecoglossus altivelis) which had mean body weight of 4.2 or 9.2 g during the rearing period after direct immersion in underground water containing lyophilized formalin-killed cells or sonicated cells of Vibrio anguillarum. A high level of protection against vibriosis was found in fish immersed directly in 0.94 or 9.4 (wet) g/l lyophilized or sonicated bacterin. The efficacy was no different for fish with a mean body weight of 4.2 g immersed for 1, 3, or 10 min in 1 (wet) g/l lyophilized bacterin. The duration of protective immunity in fish with a mean body weight of 8.0 g lasted 60 days after direct immersion in 0.94 or 9.4 (wet) g/l of lyophilized bacterin.

Ayu Plecoglossus alaivelis were immersed for 3 min in a 5% NaCl solution containing 1% lyophilized formalin-killed Vibrio anguillarurm. Two months after vaccination, each of the four experimental groups vaccinated fish were infected by intraperitoneal (i.p) injection of either 103, 104, or 106 cells of V. anguillarum PT479 streptomycin resistant (Smr)-strain or exposed to 106 cells/ml of PT479 Smr strain. The time period of elimination of the infecting organism depended on the number of cells of V. anguillarum given to the fish. The challenge organisms wera virtually eliminated within 6h after i.p. injection of 103 or 104 PT479 Smr cells in the blood and intestinal tracts. On the other hand, organisms increased 12h after injection of 103 or 104 cells/ml in non-vaccinated fish, reaching 106 cells/ml of blood and 105 cells/g in the intestinal tracts by 72h. The challenge organisms were observed in the blood and intestinal tracts of vaccinated fish Within 24h after i.p. injection of 106 cells. Subscquentry, the organisms decreased to 10 cells or less. The number of organisms increased in non-vaccinated fish after i.p. injection of 106 cells. The number of challenge organisms was 10 cells/ml or g, or less, in the blood and the intestinal tracts of vaccinated fish 72h after exposure to 106 cells. The challenge organisms were also ob-served in the blood of non-vaccinated fish for 72h.

Two-hundred eighty-one strains of Pasteurella piscicida were collected from cultured yellowtail (Seriola quinqueradiata) in various districts of Japan between 1981 and 1983. Two-hundred sixty-two strains were resistant to combinations of chloramphenicol (CP), tetracycline (TC), ampicillin (APC), kanamycin (KM), nalidixic acid, furazolidone, and/or sulfamonomethoxine (SA). Transferable R plasmids were detected in 168 out of the 262 strains. The most common types of detected R plasmids were those encoded with resistance to CP, TC, and SA, and also those markers containing KM. Fortyone strains carrying APC-resistance had appeared first in 1982, and a transferable R plasmid was also detected for the first time.The R plasmids encoded with different resistance markers were constructed from common DNA sequences. Identical digestion patterns were observed in R plasmids detected from various areas. There was strong homology with these R-plasmid DNA. Consequently, the multiple drug-resistant strains of P. piscicida, carrying an R plasmid with the same DNA structure, were distributed in yellowtail culture farms in various areas.

The susceptibility of various chemotherapeutic agents against five hundred and sixty one strains of non-hemolytic Streptococcus sp. were tested. These strains were collected from streptococcal infection of marine fish, yellowtail Seriola quinqueradiata, from 1974 to 1981 in various districts of Japan. The fifteen kinds of chemotherapeutics used were ampicillin (ABP), cephalexin (CEX), cephazoline (CEZ), chloramphenicol (CM), tetracycline, streptomycin (SM), kanamycin (KM), erythromycin (EM), leucomycin (LM), josamycin (JM), triacetyloleandomycin (TAO), lincomycin (LIM), nalidixic acid (NA), furazolidone (NF), and sulfamonomethoxine (SA). Four hundred and eleven strains isolated from 1978 to 1981 were additionally tested for sensitivity to doxycycline, trimethoprim (TMP), and ormethoprim (OMP), and one hundred and fifty nine strains isolated in 1981 were also tested for sensitivity to spiramycin (SP). EM was the most effective against the strains among the tested drugs, with all strains inhibited at a concentration of 0.1μg/ml or less. Successively, ABP, tetracycline derivatives, JM, TAO, and LIM had high antibacterial activity, and their MIC values for 90% of the strains were 1.24μg/ml or less. These strains were sensitive to CM, CEZ, KM, and SP, and moderately sensitive to CEX, SM, NF, TMP, and OMP. The strains of Streptococcus sp. were intrinsically resistant to NA and SA. Key words: yellowtail, fish disease, fish-pathogenic bacteria, streptococcal infection, non-hemolytic Streptococcus sp., drug susceptibility.

The therapeutic efficacy of a 1 : 3 combination of ormetoprim-sulfamonomethoxine (OMPSMM), oxolinic acid (OA), and miloxacin (MLX) was evaluated against drug resistant strains of Edwardsiella tarda. These resistant strains carried on R plasmid encoded with resistance to chloramphenicol, tetracycline, and sulfonamide. Fish were injected intraperitoneally with the bacterium and orally dosed with various level of OMP-SMM, OA, and MLX for five days. Appropriate positive and negative controls were incoporated into the study. A dose of at least 25 mg/kg/day of a combination of OMP-SMM, 12.5 mg of OA, and 6.2 mg of MLX provided protection. Our results indicated that OMP-SMM, OA, and MLX were effective against the infection with drug resistant strain of E. tarda.

Summary A 562 base pair fragment of DNA from a serotype A strain of Vibrio anguillarum was cloned into pUC9 and used as a hybridization probe for the rapid identification of Vibrio anguillarum by colony hybridization. The probe was tested on nine different fish pathogens, 15 Vibrio isolates, 2 organisms closely related to Vibrio, and 9 serotypes of V. anguillarum. The probe hybridized only with the DNA of V. anguillarum serotypes A and H. The sequence of the 562 nucleotides have been determined. This probe allows rapid, reliable, and specific detection of V. anguillarum in freshwater ayu, Plecoglossus altivelis.

An enzootic caused by bacteria occurred among cultured giant gourami in two freshwater fish farms in Kagoshima, Japan, in 1982. Typical external characteristics of the diseased fish were sloughed scales, exophthalmia, and opaque eyes. Internally, numerous creamy white nodules were found in the gills, spleen, kidney, and liver and a lesser number in the bladder and stomach. Nocardia sp. was isolated from spleen and kidney tissues of all diseased fish examined. To clarify the taxonomic position of the isolates, 164 tests were performed, and results were compared to reference strains of six species of Nocardia and one species of Rhodococcus. The isolates formed a homogenous group in a single taxon at a similarity of 98.7% based on an average linkage analysis and were clearly separated from the reference strains. The isolated strains were more similar to Nocardia kampachi than to the other representative species. However, 12 distinct differences were found between the isolates and N. kampachi, includ...

Bacterial flora in the gut of wild cultured prawns, Penaeus japonicus Bate, were investigated and the isolated strains were classified to genera. The flora in the water and mud environment which the prawn inhabits were also investigated. In the water of the prawn culture tank, the highest bacterial number was counted in the zoea stages (1.8 × 105 /ml) and the numbers decreased from the end of the mysis stage to the postlarval stage. Few differences in composition were observed between the two populations. In the digestive tract of the zoea, Vibrio spp. were the dominant genera. In the adult stage, Pseudomonas spp. were the most abundant in the flora of the digestive tract of prawns cultured for 126 days. One prawn that grew poorly had large numbers of the Aeromonas and Vibrio groups in the digestive tract. In the digestive tract of wild prawns, the Pseudomonas group was the dominant bacterial population.

The cellular immune response of rainbow trout Salmo gairdneri immunized by immersion or injection with Vidrio anguillarum bacterin was investigated using the passive antibody producing cell assay and passive antidody rosette-forming cell assay. Antibody-producing cels (plaqueforming cell: PFC) were rarely detected in the anterior kidney and spleen of raindow trout immunized by immersion. PFCs were detected in fish immunized by injection and reached the maximum level on the 13th day after immunization. The number of antigen-bingding cells (rosette-forming cells: RFCs) increased rapidly in the anterior kidney and spleen of rainbow trout vaccinated by immersion or injection. The RFC reached the maximum level on the 11th day after immunization. After that the number of RFCs gradually decreased until it reached the same level as that in non-immunized fish on the 28th day. The hemagglutinating antibody of the serum against V. anguillarum of fish vaccinated by immersion tended to be as low as the serum of non-vaccinated fish. However, the hemagglutinating antibody in fish vaccinated by injection was detected first on the 13th day after immunization. The maximum value of the titer was reached on the 28th day after immunization.

In a Vibrio anguillarum strain passaged through ayu (Plecoglossus altivelis), the LD50 value against ayu by the water-borne challenge method did not change from that of the original strain freshly isolated from diseased fish. The ayu were reproducibly infected with the passaged strain by the water-borne method in which the fish were first exposed to 5.32% NaCl solution and then to a suspension of V. anguillarum cells. The symptoms in ayu infected by this challenge method were observed to be very similar to the symptoms of a natural vibriosis infection. The LD50 value against fish exposed first to NaCl solution and then to the cell suspension was lower than that of fish exposed to only the cell suspension. This challenge method, incorporating initial exposure to a 5.32% NaCl solution followed by exposure to a Vibrio cell suspension, provided a clear difference in mortality between vaccinated and non-vaccinated fish.High level protection against vibriosis was observed in fish vaccinated by immersion in V. anguillarum cells which had been formalinized, washed, and pelleted or which had been formalinized, washed, and lyophilized.

Streptococcal infections have been frequently observed in cultured freshwater fish, tilapia (Tilapia nilotica), rainbow trout (Salmo gairdneri) and ayu (Plecoglossus altivelis) at farms in various districts of Japan. The causative agents isolated from diseased tilapia, rainbow trout and ayu had the same morphological as well as biochemical characteristics. All the strains were also serological homogeneous. These strains were found to be pathogenic to freshwater fish after intraperitoneal injection. The autoclaved and hot-HCl treated cells did not react with any of the group specific sera used: Lancefield A, B, C, D, E, F, G, H, K, L, M, N, O and MG. This organism was not identical to any strains of Streptcoccus previously reported.

One hundred sixty eight strains of Edwardsiella tarda collected from cultured eel (Anguilla japonica), tilapia (Tilapia nilotica) and channel catfish (Ictalurus punctatus), and from water and plankton of culture ponds were studied for their sensitivities to 10 chemotherapeutic agents: chloramphenicol (CM), tetracycline (TC), streptomycin (SM), kanamycin (KM), aminobenzyl penicillin (ABP), cefazolin (CEZ), nalidixic acid (NA), furazolidone (NF), sulfamonomethoxine (SA) and trimethoprim (TMP). All strains were highly sensitive to CEZ and TMP. Only 32 of 168 strains were sensitive to all the drugs tested. The remaining 136 strains were resistance to various combinations of the 8 drugs (CM, TC, SM, KM, ABP, NA, NF and/or SA). The most common types of drugs resistance were to combinations of CM, TC, NF and/or SA.Transferable R plasmids were detected in 38 out of 136 resistant strains. The most common type of resistance markers of R plasmid was CM, TC and SA. Other R plasmids had markers for resistance to TC, SA, TC SA and CM TC SM KM SA.Cryptic plasmids were also detected in all strains E.. tarda tested by agarose gel electrophoresis.

A comparison of the biochemical and serological characteristics of atypical Aeromonas salmonicida strains isolated from eel (Anguilla japonica), goldfish (Carrassius auratus), and reference strains of A. salmonicida were reinvestigated.The biochemical and serological properties of causative agents of ulcer disease in eel at Tokushima and Shizuoka prefecture, and Hiroshima University in Japan were similar with isolates previously described. Several biochemical characteristics distinguished the isolates reported here from atypical A. salmonicida strains from goldfish, eel, and typical A. salmonicida.The DNA base composition (mol% guanine plus cytosine) of the isolate was similar with those of some atypical and typical A. salmonicida previously described.The thermostable antigenic structure of atypical and typical A. salmonicida were similar to the isolate reported here. The thermolabile antigenic structures showed some differences among the strains.The structure of lipopolysaccharide (LPS) from all strains demonstrated identical pattern by electrophoretic analysis.

One hundred and seventy-five strains of Aeromons salmonicida isolated in cultured salmonid fish and wild salmonid fish from rivers in Japan from 1979 to 1981 were tested for theri susceptibility to 12 chemotherapeutics. Five of 129 (3.9%) strains isolated in the cultured fish were sensitive to all the drugs tested. The remaining 124 strains were resistant to from one to six drugs; in particular, nalidixic acid derivatives and/or nitrofuran derivatives. Transferable R plasmids were detected in only 2 out of the 124 resistant strains. The resistant marker of the detected R plasmids determined as a combination of chloramphenicol (CM), streptomycin and sulfonamides (SA). The molecular weight of the R plasmids was 29M daltons. Non-transferable R plasmids resistant to TC were detected in two A. salmonicida strains habouring transferable R plasmid and had a molecular weight of 7.6M daltons. On the other hand, 32 strains (69.6%) isolated in wild salmonid fish were sensitive to all the drugs tested. The remaining strains were resistant to SA, and to a combination of CM, colistin and SA. These resistant strains had no transferable R plasmids.

The purpose of the present study was to explore the potential usefulness of the fluorescent antibody technique for rapid diagnosis of pseudotuberculosis in yellowtail (Seriola quinqueradiata). The causative bacteria of pseudotuberculosis have been successfully identified 100% by means of the direct fluorescent antibody technique. These appear as specific fluorescing particles in impression smears prepared from organs of infected fish with the white granules which were regarded as characteristic lesions of the disease.Moreover, diagnosis was made in all specimens within two to three hours after the specimens were received at the laboratory. It was revealed that the direct fluorescent antibody technique could be employed as a rapid diagnostic procedure of pseudotuberculosis in yellowtail instead of the conventional culture method.

For the past several years “bacterial tuberculoioidosis” has caused severe losses among young fishes of Seriola quinqueradiata and S. purpurascens cultured in various parts of Japan. The name “bacterial tuberculoidosis” was proposed by KUBOTA et al (1970) on th basis of the symptomatology and histopathology of the disease, though the causative agent responsible for it was not isolated.The present authors succeeded repeatedly in isolating the causative bacterium in pure culture from lesions of spleen and kidney of affected fish which were obtained on the occasions of outbreaks of the disease in Miyazaki, Oita and Ehime Prefectures during the period from 1969 to 1970. The bacterium when inolulated into Seriola caused the same pathological features as seen in naturally affected fish and killed them. The bacterium grew well on Brain heart infusion agar containing fresh human or rabbit blood and Brain heart infusion broth containing rabbit serum, both with 3% NaCl, but very poorly on ordinary nutrient agar or broth with 3% NaCl.In 2-day old cultures, grown on blood agar, cells were straight or slightly curved rods of 0.6 by 1.6 microns in the average size and arranged singly, in pairs or in chains. They were Gram-positive in young cultures but changed into Gram-negative after about 18 hours generally. Cells exhibited pleomorphism and had metachromatic granulus at the both ends of the cells. They did not form spores and were non-motile in semisolid agar madia. Capsules were absent.The bacerium was a facultative anaerobe. Nitrates were not reduced and neither indole (Kovac's method) nor hydrogen sulfide was produced. The oxydase test, methyl red test and catalass test were all positive, and the Voges-Proskauer test was negative. Gelatin was not liquefied. Agar Plates containing rabbit erythrocytes showed alpha-hemolysis. Acid was produced from glucose, mannose, levurose and galactose, but other sugars tested were not fermented. The bacterium was definitely sensitive to penicillin.On the basis of these observations, it is assumed that this organism is more closely related to the genus Corynebacterium than to any other known genera.

Protection and serum antibody production against Aeromonas hydrophila was examined in nile tilapia, Tilapia nilotica (L.). Intraperitoneally injected formalin-killed and Freunds complete adjuvant vaccines were compared using different doses (2.9 × 10 7 and 2.9 × 10 9 cfu/ml). Upon challenge, the protective ability and antibody titers resulting were significantly different between vaccinated and unvaccinated groups. A relative level of protection of 100% was obtained within two-weeks, and a maximum level of 53 – 61% protection was found one-week post-vaccination.

Two hundred twenty-six strains of Vibrio anguillarum collected from cultured ayu (Plecoglossus altivelis) between 1978 and 1980 were studied for their sensitivities to 10 chemotherapeutics. In order to determine whether the drug-resistant strains possessed transferable R plasmids, they were conjugated with Escherichia coli. Almost all the strains isolated during the 3 years showed resistance to nalidixic acid (NA) and/or furazolidone (NF). NA and NF resistance were not transferred to Escherichia coli from any of the strains. Chloramphenicol-resistant strains were isolated in every year and almost all of them carried transferable R plasmids. Only one strain with tetracycline resistance was found among the strains tested. Strains resistant to sulfonamides, streptomycin, ampicillin (ABP), and trimethoprim (TMP) increased rapidly in 1980, and a large number of them carried transferable R plasmids. Transferable R plasmids encoded with resistance to ABP and TMP were detected for the first time in V. anguillarum strains. The R plasmids detected in the strains isolated in 1980 were classified into incompatibility groups E, A, and an untypable group. The R plasmid DNAs were cleaved by EcoRI to yield 11 to 13 fragments. The estimated molecular weights of the R plasmids from the five strains ranged from 97 to 104 M daltons.