| Aeromonas veronii as an important aquatic organisms pathogen and zoonotic pathogen not only causes serious economic losses of the aquaculture industry, but also can be passed through water-borne, foodborne dissemination and wound infection, which caused illnesses such as pneumonia, septicemia and food poisoning. Meanwhile, abusing the antimicrobial agents makes the drug resistance of Aeromonas veronii intensified,thus it brings new diffculties to freshwater fish disease prevention and controlling. Aeromonas veronii were isolated from different kinds of freshwater fishes in northeast of China.By pathogen separation identification, drug resistant analysis, integrase detection and drug resistant gene-cassette, identified Aeromonas veronii infection, drug resistant and resistance gene diversity of different freshwater fishes in northeast. Therefore, it provides a theoretical basis for guiding the clinical medicine of aquaculture and further researching of resistance mechanisms. 1 Aeromonas veronii separation and identification from different freshwater fishesSuspicious materials were collected from different freshwater fishes in different regions of the three northeast provinces by epidemiological investigations. 52 Aeromonas veronii strains with pathogenicity were isolated by isolation and culture, smear microscopy, physiological and biochemical identification, pathogenicity test and 16 s rDNA sequence analysis. And there was different pathogenicity and biological characteristics among different strains. 2 Bacterial drug resistance analysis from different freshwater fishesIn order to provide a reference for guiding clinical medication to aquaculture, minimal inhibition concentrations(MIC) of 52 strains were tested by the microdilution method and analyzed drug resistance. The results shows there are serious drug resistance in these 52 strains and the MIC results are different from Aeromonas veronii strains separated from different regions. For gentamicin, amoxicillin, erythromycin were all resistant; Amikacin and azithromycin had high resistance rate; Then followed by ciprofloxacin, doxycycline and enrofloxacin, the resistance rates were 78.85%, 63.46% and 57.69%, respectively; The rates of florfenicol and chloramphenicol were the lowest at15.38% and 11.54%; and these strains occurred multidrug resistance, they were resistant to 6, 7, 8, 9, 10 and all drugs, among them isolates resistance to 8 and 9 drugs were most widely distributed, the resistance rates were 26.92% and 36.54% respectively. 3 Integrase assay and positive integron/gene cassette system analysisIsolated Aeromonas veronii strains were tested for ClassⅠ, ClassⅡ, ClassⅢ intergrase assay, determined and did sequence analysis to 3 ’conserved region and variable region gene cassettes of intergrase-positive bacterial strains. The results indicated that isolated bacterial strains were all carrying ClassⅠintegron, and all strains were not carrying ClassⅡand ClassⅢintegron; the structure of ClassⅠwas Intact, there was 3’conserved region with sulⅠ, qacE and ORF5 genes, and 14 Aeromonas veronii strains with intact Class Ⅰ integron had resistance gene cassette system, the detectioin rate was 26.92%. There were four different resistance gene cassette systems in 14 bacterial strains, they were aadA1-catB, drfA-orfF-aadA1, aac(6′)-Ib-cr-arr3-drfA-aadA1 and drfB-catB-aadA1. Among them, aadA1-catB and drfA-orfF-aadA1 were more in Aeromonas veronii, respectively were 5 strains and 6 strains, in addition, there was a resistance gene cassette system with 4 resistance genes(aac(6′)-Ib-cr-arr3-drfA-aadA1) in AJ-J2 bacteria, it could mediated bacteria to have drug resistance to sulfa antibiotics, quaternary ammonium biocides, trimethoprim and aminoglycoside antibiotics. |
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