Abstract:

To investigate the causes of disease and analyze the characteristics of pathogenic bacteria, providing a theoretical basis for the prevention and control of disease in Crucian carp, bacteria were isolated and purified from the liver and intestine of diseased Crucian carp. The isolated bacteria underwent 16S rRNA sequence analysis, artificial infection test, physiological and biochemical identification, and phylogenetic tree construction and a drug susceptibility test using disk diffusion method to screen for sensitive drugs. Strain A was isolated from the liver and intestines of diseased fish. Based on 16S rRNA gene sequence determination, biochemical identification and phylogenetic tree construction, strain A was identified as Proteus vulgaris. Artificial infection test confirmed that strain A was the pathogenic bacterium, with an LD₅₀ of 9.77×10⁶ CFU/tail. Strain A was susceptible to 6 agents, including cefazolin, cefadroxil, flufenicol, kanamycin, azithromycin and gentamicin. It was resistant to 5 antibiotics, including amoxicillin, erythrocin, neomycin, clindamycin and doxycycline. The results of this experiment indicated that strain A is the Proteus vulgaris, the main culprit of the disease. Based on the drug sensitivity test, highly sensitive antibiotics can be selected for clinical treatment.

Key words: Proteus vulgaris, Crucian carp, carp disease, etiology, antimicrobial susceptibility testing, identification, antimicrobial susceptibility, biological characteristics, antibiotic treatment