Genetic and virulence characterization of Streptococcus suis type 2 isolates from swine in the provinces of Zhejiang and Henan, China

Abstract

This study was aimed to examine the genetic characteristics of 44 Streptococcus suis type 2 (SS2) isolates and the virulence attributes of 23 representative isolates. Multilocus sequence typing revealed five sequence types (ST1, ST7, ST28, ST86, and ST162) with 19 isolates assigned to ST7 (43.2%), 14 to ST1 (31.8%), and 9 to ST28 (20.5%). PCR typing of the pilus gene clusters classified the isolates into three types: A (72.7%), B (22.7%), and N (4.5%). All isolates of pilus types A and N were assigned to the ST1 complex containing ST1, ST7, and ST86, while those of type B belonged to the ST27 complex comprising ST28 and ST162. Only two strains had the putative pathogenicity island 89-kb cluster (89K) and were of type N. The type B strains had a significantly lower adhesion, were more readily killed by macrophage, and had lower virulence to mice than those of types A and N. We conclude that SS2 strains of both ST1 and ST27 complexes, parallel to pilus types A and B, were prevalent in the pig populations in Zhejiang Province, and ST7 and ST1 strains were the predominant genotypes in the diseased pigs with pneumonia.