Abstract
BackgroundOur previous studies revealed that a new disease form of streptococcal toxic shock syndrome (STSS) is associated with specific Streptococcus suis serotype 2 (SS2) strains. To achieve a better understanding of the pathogenicity and evolution of SS2 at the whole-genome level, comparative genomic analysis of 18 SS2 strains, selected on the basis of virulence and geographic origin, was performed using NimbleGen tiling arrays.ResultsOur results demonstrate that SS2 isolates have highly divergent genomes. The 89K pathogenicity island (PAI), which has been previously recognized as unique to the Chinese epidemic strains causing STSS, was partially included in some other virulent and avirulent strains. The ABC-type transport systems, encoded by 89K, were hypothesized to greatly contribute to the catastrophic features of STSS. Moreover, we identified many polymorphisms in genes encoding candidate or known virulence factors, such as PlcR, lipase, sortases, the pilus-associated proteins, and the response regulator RevS and CtsR. On the basis of analysis of regions of differences (RDs) across the entire genome for the 18 selected SS2 strains, a model of microevolution for these strains is proposed, which provides clues into Streptococcus pathogenicity and evolution.ConclusionsOur deep comparative genomic analysis of the 89K PAI present in the genome of SS2 strains revealed details into how some virulent strains acquired genes that may contribute to STSS, which may lead to better environmental monitoring of epidemic SS2 strains.
Highlights
Our previous studies revealed that a new disease form of streptococcal toxic shock syndrome (STSS) is associated with specific Streptococcus suis serotype 2 (SS2) strains
We identified a number of novel genetic polymorphisms in SS2 strains and several candidate virulence factors that may contribute to STSS
We used NimbleGen tiling arrays to analyze the genomic variability of 18 SS2 isolates (Table 1), including five strains (ZYH214, ZYH215, ZYH354-1, Habb, and 98T003) isolated from STSS patients during the two Chinese SS2 outbreaks, two strains (JR and JZD-1) isolated from dead pigs during the 2005 outbreak in China, eight virulent strains isolated from China before the 1998 outbreak or from other countries, and three avirulent strains (05HAS68, ZF, and T15)
Summary
Our previous studies revealed that a new disease form of streptococcal toxic shock syndrome (STSS) is associated with specific Streptococcus suis serotype 2 (SS2) strains. Comparative analysis of the whole-genomic DNA sequence of the European S. suis strain P1/7 (by the Sanger Institute) and two representative highly virulent strains (98HAH12 and 05ZYH33) isolated from STSS patients during the two epidemic outbreaks in China uncovered a candidate pathogenicity island (PAI) named 89K, which has been confirmed to undergo horizontal gene transfer (HGT) by our recent work [5]. Results from a recently published work suggest that S. suis strain BM407, which was isolated from a human meningitis case in Vietnam in 2004, contains two regions with extended similarity to 89K [7] These findings led us to hypothesize that the genome of SS2 would be highly polymorphic among different strains
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