Abstract:

[Objective] A goat death case caused by respiratory symptoms in a farm was etiologically diagnosed, and the antimicrobial susceptibility and pathogenicity of the isolated bacterial pathogen were characterized. [Method] The dead goat was dissected and the lung and trachea tissues were collected in sterile conditions. The clinical samples were incubated on TSA solid medium and cultured at 37 ℃ for 22-24 h. After purification, the suspected bacterial colonies were subjected to Gram staining, microscopic examination and biochemical identification. The phenotypically identified strain was molecularly comfirmed by 16S rDNA PCR amplification, sequencing, phylogenetic tree construction and homology analysis. The antimicrobial susceptibility test of the isolate was performed with broth micro-dilution method. The pathogenicity of the isolate to goat kid was determined by using an animal challenge test. [Result] A bacterial strain designated as DMQ-Y-Mh was isolated from the clinical samples. The isolate was observed as Gram-negative bacilli under microscope, and was identified as Mannheimia haemolytica following biochemical identification as well as 16S rDNA PCR amplification, sequencing and homology analysis. It was sensitive to ciprofloxacin, azithromycin and gentamicin, moderately sensitive to levofloxacin, oxytetracycline and florfenicol, and resistant to tilmicosin, enrofloxacin and tylosin. Within 72 h of the challenge with the isolate, the goat kid perished, and the trachea and lung bronchi contained viscous secretions. There were dark red lesions in the lung tissue, and the boundary with the normal lung tissues was obvious. Mannheimia haemolytica could be isolated from the lung and trachea tissues of the dead goat kid again. [Conclusion] Mannheimia haemolytica was the pathogenic agent that caused the death of goat in the farm. The results of the antimicrobial susceptibility test served as a guide for clinical medication.

Key words: goat, Mannheimia haemolytica, isolation and identification, antimicrobial susceptibility test, pathogenicity