¹Department of Veterinary Medicine, Rongchang Campus of Southwest University, Chongqing, 402460 CHINA
²Chongqing Engineering Research Center of Veterinary Science, Chongqing, 402460 CHINA DOI : 10.9775/kvfd.2017.18405 Pasteurella multocida (P. multocida) causes fowl cholera in birds and the pathogenesis and virulence factors involved are still poorly understood. TonB protein is a periplasmic protein prevalent in a large number of Gram-negative bacteria, as in Pasteurella, which is believed to be responsible for the import of ferric iron complexes across the outer membrane and plays a role as an important virulence factor to help bacteria to obtain nutrients. In this study, a total of 23 isolates of P. multocida were obtained from 172 cases of clinical respiratory disease in duck and geese, giving an isolation rate of 13.4%. P. multocida Serogroup A was isolated from 22 cases (95.7%), whereas serogroup F was from 1 case (4.3%). All isolates were analyzed for their susceptibility to 15 antibiotics and the presence of 18 genes for virulence factors. The susceptibility profiles suggested that Tetracycline, Cephalosporin, Enrofloxacin, and Aminoglycosides were the drugs most likely to be active against P. multocida. However, 78.3% and 52.2% of poultry strains were resistant to Penicillin and Sulfisoxazole, respectively. PCR results showed that ptfA, fimA, tonB, fur, hgbA, hgbB, sodA, sodC, pmHAS, nanH, nanB, plpB and ompH genes occur in most poultry strains of P. multocida. The virulence genes such as toxA, tadD, hsf-1, pfhA and ompA were each present in <73.9% of strains. The tonB gene was detected in all 23 clinical strains of P. multocida which were recovered from different hosts and harboring different serotypes. Phylogenetic analysis indicated that these tonB genes of P. multocida from different hosts and harboring different serotypes have close genetic relationship with a high similarity. Multiple sequence alignment demonstrated that TonB protein of Gram-negative bacteria exists in multiple conserved sites, such as -xSSGx-, -YP-, -LD- and xA[A/V]Lx motif. These findings provide clinical data into the epidemiological and molecular characteristics of avian P. multocida isolates and provide a reference for the researches of drug target in P. multocida. Keywords : Antimicrobial susceptibility, Capsular antigens, Pasteurella multocida, tonB gene, Virulence gene, cloning, Phylogenetic analysis