Abstract: [Objective] To isolate and identify Mannheimia haemolytica from sheep in Kaifeng City, Henan Province, analyze its biological characteristics, and understand its drug resistance and the presence of virulence genes. [Methods] A total of 530 nasopharyngeal swabs were collected from sheep with respiratory diseases in 8 sheep farms in Kaifeng City. Mannheimia haemolytica was isolated using Tryptic Soy Agar （TSA）. The isolated strains were identified through biochemical reactions, morphological observations, and detection of the specific gene LKT. Multiplex PCR was used for serotyping of the isolates. PCR was employed to detect virulence genes in the isolates. The sensitivity of the isolates to 12 antimicrobial agents was tested using the Kirby-Bauer （K-B） disk diffusion method. Pathogenicity tests of isolates were conducted using BALB/c mice. [Results] ①A total of 52 strains of Mannheimia haemolytica were identified from the 530 samples, with a detection rate of 9.81%. ②Serotyping of the isolated Mannheimia haemolytica revealed that 17 strains belonged to serotype 1, accounting for 32.69%; 28 strains belonged to serotype 2, accounting for 53.85%; and 7 strains belonged to other serotypes, accounting for 13.46%. ③Detection of 11 virulence genes in Mannheimia haemolytica showed that all genes were detected. The detection rates of gcp, lktC, and nanH were relatively high, at 73.08%, 67.31%, and 65.38%, respectively, while the detection rates of the remaining virulence genes ranged from 17.31% to 51.92%. ④The isolated strains were highly sensitive to cefotaxime, cephalexin, and ceftriaxone, with sensitivity rates of 86.54%, 78.85%, and 84.62%, respectively. The sensitivity rates to the remaining drugs ranged from 11.54% to 46.15%, among which the sensitivity rates to erythromycin, gentamicin, and ampicillin were lower than 20%. ⑤Pathogenicity tests in mice showed that the lethality rates of Mannheimia haemolytica of serotype 1 and serotype 2 were both 100% within 36 hours. [Conclusion] The Mannheimia haemolytica isolated and identified from sheep nasopharyngeal swabs in the Kaifeng region primarily exhibited two serotypes, carried multiple virulence genes, and demonstrated high pathogenicity. The research results provide data references for the rational use of drugs and scientific prevention and control of Mannheimia haemolytica infections in sheep in Kaifeng City.

Key words: sheep, Mannheimia haemolytica, isolation, identification, virulence genes, drug resistance