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J. Clin. Microbiol. doi:10.1128/JCM.01438-07
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Pattern of accessory genes predicts the same relatedness among strains of Streptococcus pneumoniae as sequencing house keeping genes: a novel approach in molecular epidemiology

Swedish Institute for Infectious Disease Control, Solna, Sweden; Dep. of Microbiology, Tumorbiology and Cellbiology, Karolinska Institutet, Solna Sweden

^* To whom correspondence should be addressed. Email: Birgitta.Henriques{at}smi.ki.se.

	Abstract

Relatedness between isolates of Streptococcus pneumoniae can be determined from sequences of multiple genes belonging to the core genome (MLST), that however do not provide information on gene content that may affect potential to cause invasive pneumococcal disease. Gene content data, using microarrays, were gathered for 40 clinical isolates of 12 serotypes belonging to 30 multi locus sequence types. We found that sequence variations in house keeping genes as assessed by MLST correlated well with whole genome microarray analyses identifying presence/absence among accessory genes/regions. However, isolates belonging to the same clonal complex, as determined by MLST, may not have identical gene content potentially affecting virulence. We found fewer intraclonal (same MLST sequence type) differences associated with pneumococcal serotypes of high invasive disease potential i e rarely found among carriers as compared to serotypes frequently found in carriage. Molecular typing of pneumococci based on the presence/absence of 25 genes localized to accessory regions, shows the same relatedness among pneumococcal strains as MLST. We conclude that molecular typing of pneumococci based on variation in nucleotide sequence of part of house keeping genes (MLST), correlate to presence/absence of genes in the accessory part of the genome. This co-variation is likely due to that both sequence variations and gene content variations primarily are created by recombination event in pneumococci.