Haemagglutination caused by the cells of Aeromonas salmonicida was investigated using 114 strains isolated from natural outbreaks of furunculosis in salmonids from 1967 through 1982. Haemagglutination by autoagglutinating strains was specific for erythrocytes of salmonids, including rainbow trout Salmo gairdneri, sockeye salmon Oncorhynchus nerka, masu salmon O. masou, chum salmon O. keta and coho salmon O. kisutch, but not for the erythrocytes of cyprinids and other fish species, including goldfish Carassius auratus, crucian carps Carassius spp. and tilapia Sarotherodon niloticus, or for mammals (sheep and humans). In a slide haemagglutination assay, these strains were categorized into the following two types: a haemagglutinating type and a non-haemagglutinating type for rainbow trout erythrocytes. Based on the occurrence of the two types as determined in 1978 and 1982, the results showed that the haemagglutination proceeded from a haemagglutinating to a non-haemagglutinating type in each strain. The phenotypic variation in haemagglutination corresponded with the variation in autoagglutination, which progressed from an agglutinating to a non-agglutinating type. This suggests that the haemagglutinative property is closely related to the capacity of autoagglutinating strains to adhere to salmonid erythrocytes.
Phenotypic variation in spontaneous agglutination of Aeromonas salmonicida was investigated using 114 strains isolated from naturally epizootics of furunculosis in salmonid fish in Japan from 1967 through 1982. These strains were categorized into three different types: an agglutinating (AG) type which produced cell flocks resulting in precipitation and loss of turbidity in cell suspensions; a nonagglutinating (NAG) type, representing no loss in turbidity; and an intermediate (IM), weakly autoagglutinating type. Based on the occurrence of the AG, NAG and IM types determined in 1978 and again 1982, it was shown that a transition occurs progressing from the AG to the NAG via the IM type. The strains involved in the AG and NAG types were virulent and avirulent, respectively, based on LD50 determination in rainbow trout (Salmo gairdneri). The NAG type was much less susceptible than the AG to the bactericidal activity of fresh normal rainbow trout serum, to immune bacteriolysis and to phagocytosis by cells from pertioneal exudate. When growth properties of AG and NAG types were compared under mixed culture conditions, the NAG type predominated in the culture broth 2-5 days after inoculation. In contrast, when rainbow trout were inoculated intraperitoneally with cells of both types, the NAG-type cells were selectively eliminated from the kidneys within a period of a few days. The AG-type cells, however, greatly proliferated in the kidneys and brought about clinical furunculosis. These results indicate that the AG type possesses a capacity to escape the defense mechanisms of the host by resisting the bactericidal activity of serum and phagocytosis by leucocytes.
The carbohydrase activity of Aeromonas hydrophila on 25 carbohydrate substrates was examined for: acid production, gas production, hydrolysis, oxidation, and degradation. Quantitative evaluations included zone ratio(R), rate of substrate degradation, and quantity of substrate by-products produced. All 164 A. hydrophila complex strains produced acid from fructose, galactose, maltose, mannitol, trehalose, dextrin, and glycogen; 99.4% of the strains produced acid from glucose, 98.8% from mannose, and 98.2% from glycerol. Acid production from other carbohydrates(arabinose, salicin, cellobiose, sucrose, and lactose)varied. Acid production from cellobiose and lactose was slow and weak, implying a catabolitic repression. Reactions of gas production from carbohydrates were intercorrelated, and correlated positively with gas production from formic acid. Gas production from glucose was observed in 86.6% of the strains. Gas production from other carbohydrates was observed in fewer percent. In polysaccharide utilization tests, starch and chitin were hydrolyzed by 100% and 96.3% of the strains, respectively; No strains utilized algin, pectin, or cellulose; chondrointin sulfate and hyaluronic acid were degraded by 5.5% of the strains, suggesting a chondroitinase similar to that of Proteus or Elavobacteria. Other carbohydrase reactions included esculin hydrolysis, 85.9%; gluconic acid oxidation, 78.0%; and ONPG hydrolysis, 97.5%. Correlation and Chi-square independence analysis indicated relationships among these carbohydrase reactions and showed that carbohydrase reactions were associated with isolate origin.
A simple quantitative plate assay was used to study the proteolytic activity of Aeromonas hydrophila complex. All the A. hydrophila complex strains hydrolyzed albumin, casein, and fibrinogen; most of the strains also digested gelatin (99.9 %), hemoglobin (94.3%), and elastin (73.2 %). None of the strains hydrolyzed collagen. The activity on each substrate varied from isolate to isolate. By using correlation analysis a close relationship was obtained among these proteolytic reactions, especially with albumin, casein, fibrinogen, gelatin, and hemoglobin hydrolysis. The elastin hydrolysis demonstrated a lower correlation with the other 5 proteolytic activities and implied a different enzymatic system. A higher casein and elastin hydrolytic response was found in the strains derived from human, fish, and other animal sources than those from water environments.
Ichthyophonus disease broke out among cultured ayu Plecoglossus altivelis, in the summer through spring of 1979. Diseased fish displayed pale body coloration, small open ulcers on the body surface, swollen abdomen due to accumulation of ascitic fluid and the production of small nodular lesions in visceral organs. Histopathological aspects were dissemination of multinucleate spherical bodies of Ichthyophonus and reactions against the spherical bodies by macrophages, multinucleate giant cells and granulomas in the affected visceral organs of diseased fish.
In a previous paper, the authors reported that the susceptibilities of Japanese eel (Anguilla japonica) to Edwardsiella tarda and Pseudomonas anguilliseptica were increased by exposure to sublethal concentrations of copper (100 or 250 μg-Cu/l) for 24 or 48 hours, and this was interpreted as a tertiary response to stress. In the present study, primary and secondary responses to stress caused by copper exposure were investigated. The apparent increase of corticosteroids was observed in eels exposed to copper for 12 hours. The numbers of lymphocytes and granulocytes in the 24 hour-exposed eels decreased to one third of those of control fish. It was also demonstrated by an in vitro test that phagocytic rate of leucocytes in the blood of the stressed eels lowered against E. tarda but not against Vibrio anguillarum. From these results, the increased susceptibility to the pathogens is interpreted as due to lowered phagocytosis.
In the autumn of 1978, motile aeromonad disease (Aeromonas hydrophila) occurred among ayu, Plecoglossus altivelis being cultured in ponds in Tokushima Prefecture. Symptoms of the infected fish were exophthalmia with hemorrhage and cutaneous hemorrhage in the tail and anus. Histopathological observation of exophthalmic eyes indicated extensive bacterial invasions with hemorrhage and necrosis in the conjanctiva and orbital adipose tissue, congestive choroid and separated retina. Liver showed focal hemorrhage. Spleen showed hemorrhage of pulp. Kidney showed nephrosis and hemorrhage of the hematopoietic tissue.
White spot disease by Cryptocaryon irritans broke out among cultured Japanese flounder (Paralichehys olvivaceus) in october 1983, in Mie Prefecture. About 1000 2-years old fish died of this disease within three days. Multiple white spots with a pin point size were observed in the gills. The histopathological examination revealed that many parasites penetrated under the epithelia of gill filament and lamellae causing hyperplasia of epithelial cells and mucous cells at the parasitic areas.