Hydrophila Complex Research Articles

Bacterial Diseases and Mortality of Angler-Caught Largemouth Bass Released after Tournaments on Walter F. George Reservoir, Alabama–Georgia

Abstract Largemouth bass Micropterus salmoides caught in each of eight tournaments during May-September, then released into cages and held for 4 d afterward, had postrelease mortalities averaging 25.4 ± 4.4% (±SE; N = 660), compared with 2.9 ± 1.8% postrelease mortality for largemouth bass collected by electrofishing (N = 70). On average, 8.2 ± 1.5% of fish died before the weigh-in at the tournament (initial mortality); thus, the total mortality (initial plus postrelease mortalities) of fish caught in tournaments was 33.1 ± 4.3%. In total, 242 tournament fish and 33 control fish were examined for external lesions after the 4-d holding periods. Pathogenic bacteria isolated from caged fish (tournament-caught and control) with external lesions were Aeromonas hydrophila complex, Pseudomonas spp., and Edwardsiella tarda. In addition, Flexibacter (Cytophaga) columnaris was identified in wet mounts ofgills and skin lesions. A bacterial pathogen was found in 42 of 76 tournament fish with skin lesions, but only 4 ...

Histopathology of Gill, Liver, and Pancreas, and Serum Enzyme Levels of Channel Catfish Infected withAeromonas hydrophilaComplex

Channel catfish Ictalurus punctatus infected with Aeromonas hydrophila complex were examined 2–21 d after they were moved from earthen ponds to tanks. These infections by A. hydrophila complex were categorized into three groups: (1) motile aeromonad septicemia (MAS; systemic infection and signs of disease), (2) cutaneous (infection limited to skin and the underlying muscle), and (3) latent (systemic infection but no external signs of disease). Hepatic necrosis was associated with all types of infections but was most consistently present and sometimes more severe in fish with MAS. Hepatic steatosis was also associated with MAS. Systemically infected fish, including fish with latent infections, tended to have pancreatic atrophy and necrosis. There was a lack of infiltrating leukocytes in necrotic areas of the liver and intrahepatic exocrine pancreas of infected fish, and there was no consistent relationship between infection by A. hydrophila complex and hepatic hemorrhage or hemosiderosis. Spongiosis of gill epithelium was present in fish with any of the three infection types, but fish with MAS had a more severe branchitis, as indicated by leukocytic infiltration and dilation of the central venous sinus. Fish with MAS or latent infections had enlarged nuclei in the branchial epithelium. There was a significant relationship between these gill lesions and the occurrence or severity of hepatic and pancreatic lesions. The mean activities of aspartate aminotransferase and lactate dehydrogenase were significantly increased in fish with MAS but not in fish with one of the other types of infections.

Bacterioplankton community structure and dynamics after large-scale release of nonindigenous bacteria as revealed by low-molecular-weight-RNA analysis.

A set of freshwater mesocosms (1.7 m3 each) was inoculated with large amounts of Escherichia coli, Pseudomonas putida, and their culture medium to substantially disturb the natural microbial community. To monitor microbial community dynamics, low-molecular-weight RNA (5S rRNA and tRNA) obtained directly from bacterioplankton was analyzed by using high-resolution electrophoresis. The introduced bacteria showed no significant effect on the community structure of the natural bacterial assemblage and its dynamics for 16 days. In contrast, the addition of culture medium resulted within 2 days in a reduction of community diversity due to dominance of a single 5S rRNA band from an indigenous bacterium. Partial sequencing of several 5S rRNAs demonstrated the molecular homogeneity of most of the abundant bands and enabled the identification of corresponding bacterial isolates and/or species. The dominating bacterium (around 54% of the total 5S rRNA) in the nutrient-amended mesocosms could be identified by partial sequencing as a member of the Aeromonas hydrophila complex. Another bloom of heterotrophic bacteria belonging to the Cytophaga johnsonae complex was detected in the nutrient-amended mesocosms after 13 days. The dominance of this C. johnsonae-like bacterium could even be seen in the environmental tRNAs of the bacterioplankton, where its specific tRNAs prevailed from day 13 onward. This event was also independent of the introduced nonindigenous bacteria because it occurred at the same time in all nutrient-amended mesocosms. By contrast, in the unamended experiments, a different small 5S rRNA could by observed from day 10 onward with less pronounced dominance.(ABSTRACT TRUNCATED AT 250 WORDS)

Proteases of theAeromonas hydrophilacomplex: identification, characterization and relation to virulence in channel catfish,Ictalurus punctatus(Rafinesque)

Abstract.Traditional biochemieal techniques and a stain to detect proteases in polyacrylamide gels were used to identify and partially characterize three proteases, P1, P2 and P3, produced byAeromonas hydrophilastrain Ah 22. P1 was found to be a heat‐labile serine protease with an optimum pH of 7·5, while P2 is a heat‐stable metalloprotease with an optimum pH of 8·0, and P3 is a moderately heat‐stable metalloprotease with peak activity beween pH 7 and 11. A comparison of 17 other strains of theA. hydrophilacomplex indicated that four produced P1, P2 and P3. Two strains produced just P1 and P3; one produced only P3; six produced two different serine proteases, P2a and P2b; and two produced a number of uncharacterized proteases. Virulence studies in age‐0 + channel catfish indicated no correlation between either quantitative or qualitative protease production and virulence.

Importance of Aeromonas sobria in Aeromonas bacteremia.

On the basis of DNA-DNA reassociation kinetics [1], core oligosaccharide analysis [2], and the electrophoretic mobility of selected cellular enzymes [3], recent taxonomic studies of motile spp. indicate that the group commonly referred to as the Aeromonas hydrophila complex is actually composed of nine or more distinct species, three of which are currently identifiable by using simple biochemical tests [4, 5]. Several studies have suggested that separating these groups may be of clinical as well as taxonomic interest because most enterotoxin-producing isolates are either A. hydrophila or sobria [6] and because differences in antimicrobial susceptibility between the three species have been noted [7, 8]. In addition to the above-mentioned properties, we have previously found [5] that ^90^0 of all blood isolates of submitted to our laboratory for biotyping belonged to either the A. sobria or A. hydrophila groups, with A. sobria predominating. Furthermore, studies conducted by Daily et al. [9] on the relative virulence of aeromonads in mice found A. sobria to be more pathogenic than A. hydrophila, although caviae was not separated from the latter group. We have subsequently confirmed the studies of Daily et al. [9] and have additionally demonstrated the relative avirulence of A. caviae [10]. To determine whether these biologic properties ascribed to each species in vitro correlate with manifestation of clinical disease, we have analyzed our recent experiences with bacteremia in our institution.

Extracellular proteolytic activity of Aeromonas hydrophila complex.

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.

Action of Aeromonas hydrophila complex on carbohydrate substrates.

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.

Enzymatic characterization of Aeromonas hydrophila complex by the API ZYM system.

Enzymatic characterization of 48 Aeromonas hydrophila complex isolates from various sources was determined with the API ZYM system (Analytab Products, Plainview, N.Y.). All isolates lacked valine and cystine aminopeptidases, chymotrypsin, alpha-mannosidase, alpha-fucosidase, alpha-galactosidase, and beta-glucuronidase but possessed caprylate esterase-lipase, leucine aminopeptidase, acid phosphatase, phosphoamidase, and N-acetyl-beta-glucosidase. Variability was found in the presence of alkaline phosphatase, butyrate esterase, myristate lipase, trypsin, beta-galactosidase, alpha-glucosidase, and beta-glucosidase. No significant differences were evident among the enzymatic profiles of isolates from various sources.

Action of selected antibiotics on four common bacteria associated with diseases of fish

Abstract. Four bacteria commonly associated with diseases of fish (Aeromonas hydrophila complex, Aeromonas salmonicida, Flexibacter columnaris‐like organisms and Pseudomonas fluorescens) were evaluated in a serial dilution system for susceptibility to four antibiotics commonly used in the treatment of bacterial fish diseases (chloramphenicol, erythromycin, furpyrinol and oxytetracycline). Findings were expressed as minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC). Furpyrinol was found to have the lowest MIC and MBC against A. hydrophila complex, A. salmonicida and F. columnaris‐like organisms. MIC and MBC's for oxytetracycline were complicated by the presenceof R‐plasmids, but were less than 4.0 mcg/ml for those without plasmids. Pseudomonas fluorescens was susceptible only to oxytetracycline. MIC for all groups of organisms using chloramphenicol was generally less than 16.0 mcg/ml. Susceptibility to erythromycin by these groups of organisms was greater than 16 mcg/ml.

Aetiology of an ulcerative disease in goldfish, Carassius auratus (L.): experimental induction of the disease

Abstract. Infection experiments were conducted to determine the primary aetiology of an ulcerative disease in goldish, Carassius auratus (L.). Goldfish were exposed to atypical Aeromonas salmonicida and A. hydrophila, previousl y isolated from cutaneous ulcers, and to 04 5 μm filtrates of cutaneous ulcers and kidneys from diseased fish. Fish were exposed to each preparation by intraperitoneal, intramuscular or subcutaneous injection and by a method in which a small patch of scales was removed from each side of the fish and the inoculums applied. Most of the fish injected with A. salmonicida died without developing coetaneous ulcers; however, ulcers were induced in five of the ten fish exposed by the scale removal technique. Exposure to ultra filtrates or A. hydrophila did not result in consistent ulcer formation o r death. Additional experiments showed that a 30‐min exposure of goldfish, without prior treatment, to water containing 3 × 105 colony forming units (cfu/ml) of A. salnumicida was sufficient to produce cutaneous lesions in nine often fish exposed. Multiple lesions were produced in most fish and A. salmonicida was consistently recovered. Fish exposed by similar waterborne challenge s to 6·2 × 106 cfu/ml of A. hydrophila or to 7·2 × 106 cfu/ml of another lesion isolate identified as a member of the A. hydrophila complex produced no lesions, eve n when scales were removed. The studies demonstrate that atypical A. salmonicida can initiate cutaneous lesion s characteristic of ulcerative disease, while A. hydrophila and an A. hydrophila complex organism cannot.

Bacterial Flora of Aquarium Fishes and Their Shipping Waters Imported from Southeast Asia

Seventy-three plastic containers of aquarium fish and accompanying water from Taiwan, Singapore, Bangkok, and Hong Kong were studied to determine bacterial flora. It was found that 69% of the bags of fish contained individuals with bacteremias. When tissue suspensions of fish were examined 18 genera of bacteria were noted. Fourteen genera were found associated with the shipping water. In each case the two predominating organisms encountered were Pseudomonas sp. (not aeruginosa) and Aeromonas hydrophila complex. Other organisms found included Citrobacter, Proteus, Escherichia, Micrococcus, Mycobacterium, and Flavobacterium. Mycoplasmas were not recovered.

Occurrence of R Factors Associated with Aeromonas hydrophila Isolates from Aquarium Fish and Waters

Isolates obtained from aquarium fish and aquarium waters identified as belonging to the Aeromonas hydrophila complex were examined for the presence of R factors imparting conjugal transmissibility of antibiotic resistance to tetracycline and/or sulfa drugs. It was found that 25.5% of the isolates from fish which were resistant to one or more of the screening antibiotics and similarily 14.1% of the isolates from aquarium water carried such R factors. These studies suggest that the prophylactic use of tetracycline may be a predisposing factor in the emergence of R factor-carrying strains of bacteria in aquarium water.