A capsule/lipopolysaccharide/MLST genotype D/L6/ST11 of Pasteurella multocida is likely to be strongly associated with swine respiratory disease in China.

Pasteurella multocida is a leading cause of respiratory disease in pigs worldwide. In this study, we determined the genetic characteristics of 115 P. multocida isolates from the lungs of pigs with respiratory disease in China in 2015 using capsular typing, lipopolysaccharide (LPS) genotyping, and virulence genotyping based on the detection of virulence-associated genes. The results showed that the isolates belonged to three capsular types: A (49.6%), D (46.1%), and nontypable (4.3%); and two LPS genotypes: L3 (22.6%) and L6 (77.4%). When combining the capsular types with the LPS genotypes, a genotype group D: L6 (46.1%) was the most prevalent among the strains. Among the 23 virulence-associated genes detected in this study, a small number of them displayed a certain level of "genotype-preference". We found that pfhA, hgbA, and hgbB had a close association with P. multocida LPS genotypes, while tadD was more associated with P. multocida capsular types. In addition, multilocus sequence typing (MLST) on 40 P. multocida isolates identified four sequence types: ST3, ST10, ST11, and ST16, and the distribution of ST11 was significantly higher than the other MLST genotypes. Interestingly, all of the ST11 isolates detected in this study were genotype D: L6 strains and they were 100% positive for hgbB. Our data suggest that a capsule/LPS/MLST genotype D/L6/ST11 is likely to be strongly associated with respiratory clinical manifestation of the disease in pigs.