Isolation and identification of bovine-derived Mannheimia haemolytica and Pasteurella multocida

Abstract:

[Background] Bovine respiratory disease complex (BRDC), a bovine respiratory disease characterized by bronchopneumonia, is caused by interactions of multiple pathogens and factors. The main bacterial pathogens causing BRDC include Mannheimia haemolytica (Mh), Pasteurella multocida (Pm), and Histophilus somni (Hs). [Objective] To understand the distribution and serotypes of Mh and Pm associated with BRDC in China. [Methods] We employed PCR to detect Mh and Pm in 698 samples (359 nasal swabs, 321 tracheal swabs, and 18 lung tissue samples) collected from 698 cattle across 54 farms in 16 provincial-level administrative regions including Henan, Hunan, Hubei, Zhejiang, Anhui, Shandong, Ningxia, Gansu, Guizhou, Heilongjiang, and Inner Mongolia from July 2022 to January 2024. Bacterial isolation and serotyping were performed on the positive samples. [Results] The positive detection rates of Mh and Pm in the samples were 2.15% (15/698, 95% CI: 1.2%–3.5%) and 10.32% (72/698, 95% CI: 8.2%–12.8%), respectively. Co-infection was detected in 5 (0.72%, 95% CI: 0.2%–1.7%) samples. From the positive samples, 8 strains (1 of serotype A1, 3 of serotype A2, and 4 of serotype A6) of Mh and 21 strains (17 of serotype A:L3 and 4 of serotype A:L6) of Pm were isolated. The multi-locus sequence typing (MLST) results for Mh showed that 5 out of 8 strains were of sequence type (ST) 1 (serotypes A1 and A6), and 3 strains were of ST2 (serotype A2). The 21 strains of Pm included 17 strains of ST1 (serotype A:L3) and 4 strains of ST7 (serotype A:L6). [Conclusion] This study isolated and identified the main bacterial pathogens causing BRDC in cattle with respiratory symptoms in specific regions and revealed the prevalent serotypes, virulence genes, and resistance genes. These findings lay a foundation for the development of related vaccines and offer theoretical support for the prevention and control of BRDC.

Key words:bovine respiratory disease complex;Mannheimia haemolytica;Pasteurella multocida;bacterial isolation;PCR identification