Yu-Feng Zhang, Nazierbieke Wulumuhan, Feng-Juan Gong and Borrathybay Entomack
To further investigate the role of capsule involved in virulence of Pasteurella multocida P-1059 (A:3), a hexB deleted mutant was constructed by homologous recombination. The DNA replacement was confirmed by PCR, Reverse transcription (RT)-PCR and DNA sequencing. Experiments were conducted to compare the differences of biological characteristics such as capsular structure, capsular polysaccharide content, virulence and serum resistance between the hexB deleted mutant of ΔhexB and wild-type strain P-1059, as well as the complemented strain P-1059C. And the ability of the acapsular mutant ΔhexB to induced protection against wild-type challenge in chickens. Electron microscopy examination of the ΔhexB showed the absence of capsular material compared to the P-1059 and P-1059C. The ΔhexB was sensitive to the bactericidal action of chicken serum, whereas the P-1059 and P-1059C were both resistant. The ΔhexB was highly attenuated in chickens by intravenously injection, and intramuscular administration of ΔhexB to chickens stimulated significant protection against P-1059 and the homologous strain X-73(A:1). These results demonstrated that the capsule is a major virulence factor of Pasteurella multocida serotype A:3 strains.