Recovery Of Acinetobacter Baumannii From Diseased Channel Catfish (Ictalurus Punctatus) In China

Although it is well documented that Acinetobacter baumannii is associated with human clinical infections, there are very few studies to date that report it as a pathogen for fish. In the present study, one bacterial strain was isolated from diseased channel catfish (Ictalurus punctatus) from Bingzi farm, Hefei, AnHui province, China and named as BH028, which was later identified as A. baumannii by both biochemical tests and polymerase chain reaction (PCR)-based methods. Furthermore, it is confirmed as the causative agent by infectivity study. This is the first report on A. baumannii as a virulent pathogen for channel catfish. Exophthalmia, pale liver, and empty stomach were the main clinical signs in the affected fish. The liver might be the major target organ. The minimal inhibitory concentration (MIC) tests showed A. baumannii was multiresistant to 10 antimicrobial agents tested.The main results obtained in the present study are summarized as follows:1. The diseased fish presented exophthalmia, pale liver, and empty stomach. There were no obvious histopathological changes observed in gills, kidney, and spleen of fish in treatment group compared to those in control group. The liver of fish in treatment group had a high number of vacuolar degeneration whereas no lesion was observed in the liver of the fish in control group.2. Pure colonies of Gram negative bacteria were isolated on FWA from internal organs of fish. The pure culture of A. baumannii was confirmed not only by biochemical tests but also by sequencing the bacterial 16S rRNA gene.3. The cumulative mortality of fish in treatment group was 36%. The affected fish in treatment group had the same external appearance with the fish sampled from Anhui province. The bacteria isolated from internal organs of fish in treatment group (including dead fish and surviving fish) were identified as A. baumannii.4. The MIC values of Penicillin G Sodium Salt, Gentamycin Sulfate, Streptomycin Sulfate, Neomycin Sulfate, Tetracycline HCl, Ampicillin Sodium Salt, Erythromycin, Polymyxin B Sulfate, Kanamycin Sulfate and Rifampicin were 0.782μg mL^-1, 0.782μg mL^-1, 3.125μg mL^-1, 1.563μg mL^-1, 6.25μg mL^-1, 0.391μg mL^-1, 6.25μg mL^-1, 0.391μg mL^-1,1.563μg mL^-1 and 3.125μg mL^-1, respectively.To the best of our knowledge, it is the first report that A. baumannii is identified as a pathogen for channel catfish. We should establish a good preventive management to prevent A. baumannii infection.