Abstract: Gram negative bacilli was isolated from lung of sick pig in Large-scale pig farm, the bacilli was identified as Haemophilus parasuis by physiological and biochemical identification, PCR identification and 16S rRNA gene nucleotide BLAST. Antibiotics sensitivity test showed that the isolation strain was high sensitive to erythrocin, chloromycetin, cephalothin, etc. Low sensitive to gentamycin, ofloxacin, noroxin, and resistant to sulfamethoxazole. The analysis of 16S rRNA showed that the 16S rRNA sequence homology between the isolated strain and reference strain Haemophilus parasuis AB078973(GenBank accession number) was 100%. Phylogenetic tree of 16S rRNA showed that the isolated strain was situated on the same branch with 3 serotype 5 reference strains AB078972,AB078973 and AB078974, and the nucleotide homology between the isolated strain and the 3 reference train was 99.0% to 99.4%. Therefore,the isolated strain was identified as Haemophilus parasuis serotype 5. Pathogenicity test showed that the isolated strain was highly pathogenic to laboratory mice. The isolated Haemophilus parasuis strain was named YN-1 strain.

Key words: Haemophilus parasuis; isolation; identification; 16S rRNA; sequence analysis