Genetic diversity of Streptococcus suis isolates as determined by comparative genome hybridization

Astrid De Greeff,Norbert Stockhofe-Zurwieden,Freddy M De Bree,Hoa Thi,Hilde E Smith,Constance Schultsz,Henk J Wisselink,Christoph G Baums

doi:10.1186/1471-2180-11-161

Abstract

BackgroundStreptococcus suis is a zoonotic pathogen that causes infections in young piglets. S. suis is a heterogeneous species. Thirty-three different capsular serotypes have been described, that differ in virulence between as well as within serotypes.ResultsIn this study, the correlation between gene content, serotype, phenotype and virulence among 55 S. suis strains was studied using Comparative Genome Hybridization (CGH). Clustering of CGH data divided S. suis isolates into two clusters, A and B. Cluster A isolates could be discriminated from cluster B isolates based on the protein expression of extracellular factor (EF). Cluster A contained serotype 1 and 2 isolates that were correlated with virulence. Cluster B mainly contained serotype 7 and 9 isolates. Genetic similarity was observed between serotype 7 and serotype 2 isolates that do not express muramidase released protein (MRP) and EF (MRP-EF-), suggesting these isolates originated from a common founder. Profiles of 25 putative virulence-associated genes of S. suis were determined among the 55 isolates. Presence of all 25 genes was shown for cluster A isolates, whereas cluster B isolates lacked one or more putative virulence genes. Divergence of S. suis isolates was further studied based on the presence of 39 regions of difference. Conservation of genes was evaluated by the definition of a core genome that contained 78% of all ORFs in P1/7.ConclusionsIn conclusion, we show that CGH is a valuable method to study distribution of genes or gene clusters among isolates in detail, yielding information on genetic similarity, and virulence traits of S. suis isolates.

Highlights

Streptococcus suis is a zoonotic pathogen that causes infections in young piglets
Different phenotypes of serotype 2 were described that differ in their virulence; strains can be differentiated by protein expression of virulence markers muramidase released protein (MRP), extracellular factor (EF) and suilysin (SLY) [13,14]
The dendrogram depicting the comparative genome hybridization (CGH) data (Figure 1) shows that isolates were divided into 2 clusters, A and B, whereas the negative control E. coli strain was assigned to cluster C

Summary

Introduction

Streptococcus suis is a zoonotic pathogen that causes infections in young piglets. S. suis is a heterogeneous species. The S. suis population is very heterogeneous as different serotypes, phenotypes, and genotypes are found. To date 33 capsular serotypes have been described for S. suis [2,8] of which serotypes 1, 2, 7, 9, and 14 are most frequently isolated from diseased pigs in Europe [9]. Besides variation in protein expression observed among S. suis strains, large de Greeff et al BMC Microbiology 2011, 11:161 http://www.biomedcentral.com/1471-2180/11/161 heterogeneity exists in gene composition [10,15,16,17]. Fifty-five well characterized S. suis strains of various serotypes were analyzed in this CGH study. We showed that groups of S. suis isolates can be identified by their own unique profile of putative virulence genes and regions of difference.

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Results

Discussion

Conclusion