Abstract:

In order to understand the epidemiological characteristics and antibiotic resistance of Pasteurella multocida (Pm) from pigs in China, isolation and culture of bacteria recovered from diseased and dead porcine organs from Heilongjaing, Liaoning, Jilin, Inner Mongolia, Shaanxi, Ningxia and Henan provinces were carried out. The bacteria were identified by 16S rRNA sequencing and kmt gene, and typed using capsular typing, lipopolysaccharide genotype typing, multilocus sequence typing (MLST), and pulsed-field gel electrophoresis (PFGE). The sensitivity of Pm to 8 antibiotics was analyzed by the broth microdilution method. The whole genome sequencing of the bacteria was performed using Illumina PE 150, and the antibiotic resistance genes were analyzed using the ResFinder database. Finally, the virulence of the isolates was determined through the pathogenicity experiment in mice. The results showed that the isolates formed smooth, moist colonies with a slightly convex and surface on blood agar plates, Gram staining revealed that it was red, coccus or short rod-shaped bacteria. A total of 34 isolates of Pm were obtained, including 19 isolates of capsule serotype A (55.88%), 14 isolates of capsule serotype D (41.18%), and 1 isolate of capsule serotype F. There were 8 isolates of LPS genotype L3 and 26 isolates of LPS genotype L6. MLST analysis identified 8 MLST types, with ST11 being the predominant genotype, accounting for 35.29%. Pm can be divided into 21 PFGE profiles, with obvious diversity among isolates. The antibiotic resistance results showed that the resistance rates of the 34 isolates of Pm to polymyxin B, tetracycline, florfenicol, chloramphenicol, ceftiofur, ciprofloxacin, and kanamycin were 38.23%, 35.29%, 23.53%, 14.71%, 11.76%, 8.82%, and 2.94%, respectively, and none was resistant to gentamicin. The antibiotic resistance genes detection showed that 18 isolates of Pm carried 9 types of antibiotic resistance genes, namely tet(B), tet(C), tet(L), floR, aadA14, sul2, aph(6)-Id, aph(3″)-Ib, and aph(3′)-Ia. The capsule serotype A isolates of Pm were more virulent than capsule serotype D isolates. The experimental group of mice exhibited an 100% mortality rate following intraperitoneal injection of the PmA1 strain at a concentration of 31.5 CFU·mL^-1.In conclusion, it was shown that the prevalent serotypes of the 34 porcine-origin Pm isolates were capsule serotype A and capsule serotype D, and the MLST type was ST11. The virulence of Pm capsular serotype A isolates was higher than that of capsular serotype D isolates. Moreover, PFGE revealed that there is diversity among the isolates. The study provided a theoretical basis for the development of vaccines and prevention strategies against Pm infections.

Key words: Pasteurella multocida, capsular serotypes, MLST types, PFGE, antimicrobial resistance