This study first demonstrated the prevalence and characteristics of P. multocida from rabbits in Fujian Province, southeastern of China. The results showed that infection of P. multocida was common in the 9 rabbitries of Fuzhou, Longyan and Nanping, and that co-infections of P. multocida strains of different serotypes were also detected. The prevalence rates of P. multocida in the lung samples of dead rabbits with respiratory disease ranged from 21.21% to 53.06%, suggesting that P. multocida was probable an important pathogen causing high mortality in the 9 rabbit farms in Fujian Province.
P. multocida strains were classified into 5 capsular types (A, B, D, E and F) and 8 LPS genotypes (L1-L8) [9, 10]. The 205 P. multocida isolates in this study were grouped into 4 serotypes of A:L6, A:L3, D:L6 and D:L3. In consistent with the previous reports, the isolates of capsular type A (76.10%) or LPS genotype L3 (56.10%) were the most predominate strains [6, 7, 11–13]. It was reported that P. multocida isolate of capsular type F was also detected in rabbits [6, 7, 13], and the strain was highly pathogenic for rabbits . Further efforts are needed to confirm the epidemiology and pathogenicity of P. multocida strain of capsular type F in rabbits in Fujian Province.
The 205 P. multocida isolates in this study were only clustered into 3 STs, ST10, ST11 and ST12, and the ST12 was the most prevalent sequence type (56.10, 115/205). In the PubMLST database (https://pubmlst.org/), strains belonged to the 3 STs were also found in rabbits from Spain, strains belonged to ST11 and ST12 were found in rabbits from Portugal, and strains belonged to ST12 were found in rabbits from China. Moreover, P. multocida strains belonged to other STs were also reported in rabbits in Italy and France [6, 7]. The results suggested that the sequence types of P. multocida might different according to different regions.
It was well recognized that the virulence factors contributed to the pathogenicity of P. multocida. In this study, 12 virulence factors were screened in the 205 P. multocida. The results revealed that, with the exception of toxA and tbpA genes, the 10 other virulence genes showed high prevalence rates ranging from 37.07% to 100%. The toxA and tbpA genes were absent in the all 205 isolates. It was first suggested that the toxA and tbpA genes were species-specific, which were detected in P. multocida strains from swine and bovine, respectively [15–17]. However, subsequent reports showed that the toxA and tbpA genes were also detected in P. multocida strains from other hosts, suggesting that the toxA and tbpA genes might not host specific [5, 18]. A previous report showed that the hgbB gene in the P. multocida strains of capsular type D belonged to ST11 was significantly associated with the respiratory disease in rabbits . However, other studies showed that there were not relationships between hgbB gene and pasteurellosis in swine and sheep [18, 19]. The hgbB gene was positive in the all 205 isolates. Further studies are needed to understand the pathogenic mechanisms of hgbB gene in the P. multocida strains isolated from rabbits. Interestingly, an association between pmHAS and capsular type A was observed, since the gene was only detected in P. multocida strains belonged to capsular type A in this study. The pmHAS (hyaluronan synthase) promotes the formation of hyaluronic acid, the major composition of the capsular of capsular type A P. multocida strain .
Antibiotics are still the first choice for prevention and control the infections of P. multocida . However, the imprudent use of antibiotics promoted the development of drug-resistant strains [11, 21, 22]. Although strains resistant to streptomycin, gentamycin, kanamycin and ceftriaxone were detected in the present study, no multidrug-resistant isolate was detected.