Abstract: In order to understand the pathogenic characteristics of a Gram-negative strain isolated from cows bedding litters.In this study, the isolates bacterium were identified by morphological observation, biochemical test, staining microscopy, 16S rDNA homology analysis. Drug sensitivity test was used to determine drug sensitivity, mice attack test was used to determine the virulence of the isolates. The results showed that the isolates were Gram-negative bacteria. The nucleotide sequence of 16S rDNA was 1 283 bp, the nucleotide homology with Acinetobacter johnsonii is greater than 99%. The isolated bacterium had strong pathagenicity to mice, the mortality was 80% in test group. The isolates were sensitive to 6 drugs including streptomycin, compound sulfamethoxazole, moderately sensitive to cefotaxime and cefuroxime, resistant to 4 drugs including penicillin and erythromycin. In this study, a strain of Acinetobacter johnsonii was isolated from dairy cow bedding litters, which provides a reference for the prevention and treatment of Acinetobacter johnsonii.

Key words: Acinetobacter johnsonii, diary cows, 16S rDNA, drug sensitivity test