We are reporting the development of two monoclonal antibodies which recognize ten separate isolates of Renibacterium salmoninarum. Both monoclonal antibodies recognize a 57 kDa protein doublet and several lower molecular weight antigens present in bacterial lysates. The 57 kDa antigen appears to correlate with a 57 kDa surface protein named Antigen F by GETCHELL et al. (1985).Antibody capture ELISA analysis indicates that the antibodies recognize different epitopes of the same protein (s). Cross-reactions were not observed with control bacteria or with normal chinook salmon serum proteins.
Survival and infectivity of Flexibacter columnaris was found to decline in the presence of other species of bacteria, such as Aeromonas hydrophila (a fish pathogen) or Citrobacter freundii (nonpathogenic to fish). In the in vitro experiment, among the selected combination ratios of the initial density of F. columnaris to A. hydrophila or C. freundii (1 : 1, 10 : 1, and 1 : 10), the survival of F. columnaris was markedly reduced at 1 : 10. In the in vivo experiment, F. columnaris failed to invade loach when the initial density of A. hydrophila or C.freundii was approximately 100 times as much as F. columnaris. In the presence of the competitive bacteria, the density of F. columnaris found in the mucus of fish's body surface did not change during the period of experiment. On the other hand, in the absence of competitive bacterium, the density of F. columnaris in the mucus increased gradually, reached a peak after 24-48 hours and showed visible signs of infection. In the waters sampled from four different aquaculture facilities F. columnaris did not invade loach when the density of F. columnaris added was 1/100 of the total bacteria found in the test water.
Epizootics and histopathology of BKD (Bacterial kidney disease) due to Renibacterium salmoninarum which occurred in sea-cultured coho salmon (Oncorhynchus kisutch), in northern coastal water of Miyagi Prefecture, were described. The death due to the disease was recorded from Jan. to July, 1987.Fish dying from BKD were collected from the floating net pens in May, 1987. As the external clinical signs of BKD, skin ulcers, necrosis of the trunk muscle and thickness of the epicardium were recognized, but numerous white granulomatous lesions in the kidney could not be seen clearly. Histopathological examination showed that mononuclear cells which phagocyted the bacteria infiltrated into various organs, and inflammatory lession compressed the parenchymall tissue. But granulomatous inflammation could not be seen in organs other than the liver. The bacteria were electro microscopically found in lysosome of macrophage-like cells. However, no bacteria could be found in parenchymalcells. As a result, the infectious mechanism was thought as follows : The bacteria first infected the injured skin to make lesions in muscle and penetrated into the blood vessel with macrophage-like cells, and finally reached the various organs. The cause of death was considered to be the decline of the systemic condition and particularly heart failure due to bacterial infection. But, furthermore, the detailed route of the infection should be studied in a future.
The multiplication and distribution of an atypical Aeromonas salmonicida strain, which was isolated as a causative agent of “head ulcer disease” of cultured eels, in artificially infected Japanese eels (Anguilla japonica) were studied by bacteriological culture technique. When the eels were injected intramuscularly with a lethal dose of the atypical A. salmonicida strain at 20°C, the pathogen was recovered at high concentrations (107-109 CFU/g) from the muscle of the injected site throughout the course of infection. But in the spleen and kidney very small numbers of the pathogen were detected even at the moribund stage, and the blood and brain were almost aseptic.A similar result was obtained in the eels which were artificially injured on the skin and infected with the pathogen. These data indicate that the disease does not attain to distinct septicemic condition but the local proliferation of the pathogen will be the death of the host fish, and this pathological feature is in a striking contrast to other bacterial infections of eels. It was also found that the bacterial growth was significantly inhibited both in vitro and in vivo at 30°C, which uggests that temperature manipulation of pond water will be an effective measure to control the disease.
The effects of sodium nifurstyrenate (NFS-Na) and tetracycline (TC) on the aerobic bacterial flora of rotifers (Brachionus plicatilis) were evaluated both in vivo and in vitro. In vivo, the bacterial numbers on ZoBell's 2216e agar of rotifers exposed to 5μg/ml of NFS-Na decreased slightly, but the numbers on BTB teepol agar rapidly declined from 107 to 105 CFU/g after 5 h exposure. At the same time, a decrease in the incidence of Vibrio accompanied by an increase of Moraxella or Acinetobacter was observed in the NFS-Na medicated rotifers as compared with the controls. The viable counts on the two media and microflora of rotifers exposed to 1 or 5μg/ml of TC exhibited similar pattern to those of the controls throughout the exposure period. In vitro, 60 strains of bacteria isolated from the rotifers were tested for their susceptibility to the two chemotherapeutics. All the Vibrio strains tested were sensitive to NFS-Na, the MIC values ranging from 0.1 to 1.6μg/ml. The strains of Acinetobacter, Moraxella and Pseudomonas were less susceptible or resistant to the drug. With respect to TC, most of the strains of the four genera were resistant.
A new reo-like virus was isolated from landlocked salmon around the Wu-Lin farm in the upper basin of Ta-Chia river, and designated as LSV (landlocked salmon virus). It has shown typical plaque-like syncytial CPE in tissue culture, and replicated very well in AS, BF-2, BB, CCO and CHSE-214 cell lines. But RTG-2 and TO-2 cells produced little virus. The optimal growth temperature of LSV in CHSE-214 is 20°C. The typical double-layered capsid of icosahedral virion with a 78 nm diameter was shown in electron micrography. The buoyant density of LSV in CsCl is 1.365g/ml. Those are typical characteristics of Reoviridae. However, LSV has 11 segmented ds RNA genomes and 5 major virion proteins, has aquatic animal hosts which are characteristics of aquareovirus, but is different from viruses of the defined six genera of Reoviridae. Compared to the electrophoretype of RNA genomes and virion proteins of LSV, CSV, CRV, GSV, and 13P2, the RNA pattern of LSV is closer to that of CSV, but the virion protein pattern is closer to that of 13P2. However, each aquareovirus has its own unique RNA and virion protein pattern. These results indicate that LSV is a newly discovered virus and the first aquareovirus isolated in Taiwan.
Virucidal effect of some disinfectants on baculoviral mid-gut gland necrosis (BMN) virus prepared from frozen naturally infected post-larvae was examined by infectivity experiments using larval and postlarval kuruma shrimp, Penaeus japonicus. BMN virus was inactivated by contact for 10 minutes at 25°C with 5 ppm as active principle-concentration of chlorine, 25 ppm as active principle concentration of iodine, 100 ppm of bezalkonium chloride, 100 ppm of benzethonium chloride, 0.5% of formalin and 30% of ethanol.
A new disease of Anguilla japonica which is characterized by an intense congestion of the gill filaments was histopathologically studied. In all the diseased eels studied the central venous sinuses and all other venous vessels of the gill filaments were observed to be filled with blood and markedly inflated.In part of the gill filaments it was observed that the blood once filled the central venous sinuses and other venous vessels had partly or almost entirely flowed out, leaving a marked dilatation of them. Destructive lesions were not observed in any part of the gill vasculature. No evidence of obstruction was observed in any part of the arterio-arterior vasculature. Arteriovenous anastomoses were observed to maintain the normal structure. The intense congestion of the arterio-venous vasculature in diseased eels is of essentially unknown etiology, but some physiological disturbance in cardiovasculature functions may be involved in the causation.