Open Access Highly Accessed Research article

Lateral gene transfer of streptococcal ICE element RD2 (region of difference 2) encoding secreted proteins

Izabela Sitkiewicz12*, Nicole M Green1, Nina Guo1, Laurent Mereghetti13 and James M Musser1

Author Affiliations

1 Center for Molecular and Translational Human Infectious Diseases Research, The Methodist Hospital Research Institute, and Department of Pathology, The Methodist Hospital, Houston, Texas, 77030, USA

2 Department of Epidemiology and Clinical Microbiology, National Medicines Institute. Warszawa, Poland

3 Université François-Rabelais, Faculté de Médecine, EA 3854 "Bactéries et Risque Materno-Foetal", Tours, France

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BMC Microbiology 2011, 11:65  doi:10.1186/1471-2180-11-65

Published: 1 April 2011



The genome of serotype M28 group A Streptococcus (GAS) strain MGAS6180 contains a novel genetic element named Region of Difference 2 (RD2) that encodes seven putative secreted extracellular proteins. RD2 is present in all serotype M28 strains and strains of several other GAS serotypes associated with female urogenital infections. We show here that the GAS RD2 element is present in strain MGAS6180 both as an integrative chromosomal form and a circular extrachromosomal element. RD2-like regions were identified in publicly available genome sequences of strains representing three of the five major group B streptococcal serotypes causing human disease. Ten RD2-encoded proteins have significant similarity to proteins involved in conjugative transfer of Streptococcus thermophilus integrative chromosomal elements (ICEs).


We transferred RD2 from GAS strain MGAS6180 (serotype M28) to serotype M1 and M4 GAS strains by filter mating. The copy number of the RD2 element was rapidly and significantly increased following treatment of strain MGAS6180 with mitomycin C, a DNA damaging agent. Using a PCR-based method, we also identified RD2-like regions in multiple group C and G strains of Streptococcus dysgalactiae subsp.equisimilis cultured from invasive human infections.


Taken together, the data indicate that the RD2 element has disseminated by lateral gene transfer to genetically diverse strains of human-pathogenic streptococci.