Ource usage. Recent publications suggest carbon source usage may be an important Rosiglitazone virulence trait for streptococci [40], which implies the more versatile S. suis isolates could benefit in pathogenesis. Since the core genome includes genes that are shared by all isolates included in our study, representing virulent as well as avirulent isolates, it is not very likely the core genome alone is sufficient for virulence. This is confirmed by the finding of several genes putatively involved in virulence in the RD regions of P1/7 that probably attribute to virulence or survival in the host of P1/7. However, since all isolates, including avirulent ones like T15, 12 and 16 [13,21], can colonize porcine tonsils, the core genome might be sufficient for colonization.Conclusions In conclusion, we show that CGH is a valuable method. Not only can it be used for genotyping of S. suis isolates, but CGH also gives information on phylogeny of isolates, and can be used to look for specific gene content, like virulence genes, or sequence variation among isolates. At present a disadvantage of CGH using the current microarray is the one way character of the technology; only distribution of genes present in P1/7 can be studied using the current microarray. Recently, several S. suis isolates have been sequenced adding new information to the S. suis pangenome. The Chinese human isolates were shown to contain an additional putative pathogenicity island (PI) of 89 kb compared to P1/7 [41], whereas the Vietnamese strain BM407 contained another additional PI compared to P1/7 [7]. Both PI's were shown to contain integrative and conjugative elements (ICE) not present in P1/7. The current microarray will have to be extended with genome sequences of other S. suis isolates to be PubMed ID:https://www.ncbi.nlm.nih.gov/pubmed/6833145 a better representation of the S. suis pangenome.Acknowledgements We thank Albert de Boer for his assistance in visualizing data in dendrograms using BioNumerics. This project was financially supported by the Dutch Ministry of Agriculture, Nature and Food Quality (KB-08). Author details 1 Infection Biology, Central Veterinary Institute of Wageningen UR (University Research Centre), Edelhertweg 15, Lelystad, 8219 PH, The Netherlands. 2 Centre for Poverty-Related Communicable Diseases, Academic Medical Centre, Meibergdreef 9, Amsterdam, The Netherlands. 3Oxford University Clinical Research Unit, Hospital for Tropical Diseases, 190 Ben Ham Tu, Ho Chi Minh City, Vietnam. 4Institut f Mikrobiologie, Zentrum f Infektionsmedizin, Stiftung Tier tzliche Hochschule Hannover, B teweg 2, Hannover, Germany.de Greeff et al. BMC Microbiology 2011, 11:161 http://www.biomedcentral.com/1471-2180/11/Page 14 ofAuthors' contributions AG carried out the molecular experiments, data analyses and drafted the manuscript. HJW collected the S. suis isolates and participated in the experimental infection. FMB performed statistical analysis of clustering methods. CS collected the Vietnamese isolates and helped to draft the manuscript. CGB collected and analyzed German isolates and helped to draft the manuscript. HNT analyzed the Vietnamese isolates. NSZ performed the experimental infections. HES initiated and coordinated the work described and helped to draft the manuscript. All authors read and approved the final manuscript. Conflicts of interests The authors declare that they have no competing interests. Received: 6 December 2010 Accepted: 7 July 2011 Published: 7 July 2011 References 1. Arends JP, Hartwig N, Rudolphy M,.