Abstract: 【Objective】 This study was aimed to clarify the main bacterial pathogens and their biological characteristics that cause respiratory symptoms of piglets in a large-scale pig farm in Luohe, Henan province.【Method】 Oral and nasal swabs of infected piglets and tissues and organs such as pleural effusion, lung, liver and spleen of dead pigs were collected aseptically for PCR detection of pathogens.The biological characteristics of the isolate was analyzed by isolation and culture of bacteria, morphological observation, satellite test, PCR amplification of 16S rDNA gene, construction of genetic evolution tree, multiple PCR identification of serotypes of isolated strains, pathogenicity test of mice and drug sensitivity test.【Result】 Round, smooth, moist, colorless and transparent microcolonies grew on the BHI solidplate containing V factor, but did not grow on the medium without V factor.The isolates were stained with Gram staining, and Gram-negative bacteria were seen under the microscope, mostly in the shape of a single ball club and long rod.Atypical 'satellite colony' was formed around the culture of Staphylococcus aureus.16S rDNA sequence analysis showed that the isolate was in the same branch as Haemophilus parasuis (Hps) with more than 97% similarity.The isolate was identified as Hps serotype 4.When the isolated Hps was injected into mice intraperitoneally, bleeding in various organs of the infected mice was induced, especially in lung.High doses of infection of Hps serotype 4 could cause death in mice.Drug sensitivity test showed that the strain had strong resistance to tetracycline, ciprofloxacin and co-trimoxazole compound sulfamethoxazole.After rational administration, a good therapeutic effect was achieved.【Conclusion】 A strain of Hps serotype 4 was successfully isolated, which could cause bleeding in different degrees in multiple organs of infected mice, and was resistant to tetracycline, ciprofloxacin and co-trimoxazole.This results provided a theoretical basis for the clinical diagnosis and treatment of Hps.

Key words: Haemophilus parasuis(Hps); serotype 4; isolation and identification; drug resistance