ABSTRACT
Streptococcus suis sequence type (ST) 7 has been spreading throughout China. To determine events associated with its emergence, we tested 114 isolates. In all 106 ST7 strains responsible for human outbreaks and sporadic infections, the tetracycline-resistance gene, tetM, was detected on the conjugative transposon Tn916. Horizontal transmission of tetM is suspected.
Subject(s)
Disease Outbreaks , Streptococcal Infections/transmission , Streptococcus suis/classification , Streptococcus suis/genetics , Animals , Bacterial Proteins/genetics , China/epidemiology , Conjugation, Genetic , DNA Transposable Elements , Gene Transfer, Horizontal , Humans , Phylogeny , Polymerase Chain Reaction , Streptococcal Infections/epidemiology , Streptococcal Infections/microbiology , Streptococcus suis/isolation & purification , Swine , Swine Diseases/epidemiology , Swine Diseases/microbiology , Tetracycline Resistance/geneticsABSTRACT
An outbreak of Streptococcus suis serotype 2 emerged in the summer of 2005 in Sichuan Province, and sporadic infections occurred in 4 additional provinces of China. In total, 99 S. suis strains were isolated and analyzed in this study: 88 isolates from human patients and 11 from diseased pigs. We defined 98 of 99 isolates as pulse type I by using pulsed-field gel electrophoresis analysis of SmaI-digested chromosomal DNA. Furthermore, multilocus sequence typing classified 97 of 98 members of the pulse type I in the same sequence type (ST), ST-7. Isolates of ST-7 were more toxic to peripheral blood mononuclear cells than ST-1 strains. S. suis ST-7, the causative agent, was a single-locus variant of ST-1 with increased virulence. These findings strongly suggest that ST-7 is an emerging, highly virulent S. suis clone that caused the largest S. suis outbreak ever described.
