Guangdong nongye kexue (Jul 2024)
Isolation, Identification, Biological Characterization, and Prevention and Control Drugs Screening of Aeromonas hydrophila from Cirrhinus molitorella
Abstract
【Objective】In recent years, bacterial septicemia of mud carp (Cirrhinus molitorella) occurred in Guangdong Province, China. The clinical signs of the diseased fish show as hemorrhage on the body, ascites, and enteritis. The study aims to identify the pathogen causing explosive death in mud carp, and reveal the biological characteristics of the isolates. Furthermore, the drugs and probiotics that can effectively inhibit the pathogen were screened, which will provide guidance for the scientific control and prevention of Aeromonas septicemia in mud carp.【Method】The bacterial strains were isolated and purified from the liver and kidney of the diseased mud carp, and the isolates were identified based on 16S rRNA and gyrB gene sequencing and physiological and biological characteristics analysis. The pathogenicity of the isolates was evaluated by PCR detection of virulence-related genes and artificial infection test. The antimicrobial sensitivities of the isolates were determined using the disk diffusion method. The antibacterial effects of three Bacillus velezensis strains against the isolates were evaluated by antagonistic inhibition test, and the antibacterial and bactericidal effects of 12 Chinese herbal extracts on the isolated strains were evaluated by micro-double dilution method.【Result】A total of ten isolates were isolated from diseased mud carp of 4 breeding frams, and these isolates were identified as A. hydrophila based on its morphological and biological characteristics, 16S rRNA and gyrB gene sequences analysis. Based on PCR detection results, these isolates harbored 10 virulence related genes, including act, aer, alt, ahyB, eprCAI, fla, gcaT, ast, lip and exu, belonging to the main prevalent virulence genotype (genotype Ⅰ). The results of artificial infection test showed that these isolates had high pathogenicity. The results of drug sensitivity test showed that the isolates were sensitive to aminoglycosides, tetracyclines, quinolones, sulfonamides and chloramphenicols, moreover, they were highly sensitive to the monomer curcumin. Strains B. velezensis WLYS23, CYS06 and LF01 showed strong antibacterial activity against the isolates.【Conclusion】The pathogen causing the bacterial outbreaks of mud carp is A. hydrophila, which contains 10 virulence related genes and has high pathogenicity. It is recommended to use doxycycline, enrofloxacin, or florfenicol for scientific prevention and control of bacterial diseases caused by A. hydrophila. In addition, several B. velezensis strains showed good antibacterial effects against the isolates, which indicate that they had broad application prospects as potential biocontrol probiotics. The Chinese herbal medicine curcumin has a good antibacterial activity against A. hydrophila, and curcumin is recommended as a green candidate drug for the prevention and control of Aeromonas septicemia in mud carp.
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