Genomic diversity between strains of the same serotype and Multilocus sequence type among pneumococcal clinical isolates

The important human pathogen Streptococcus pneumoniae is known to be a genetically diverse species. We haveused comparative genome hybridization (CGH) microarray analysis to investigate this diversity in a collection ofclinical isolates including several capsule serotype 14 pneumococci, a dominant serotype among disease isolates. Wehave identified three new regions of diversity among pneumococcal isolates and, importantly, clearly demonstrategenetic differences between strains of the same multilocus sequence type (ST) and capsule serotype. CGH maytherefore, under certain circumstances, prove to be a valuable tool to supplement current typing methods. Finally,we show that these clonal strains with the same serotype and ST behave differently in an animal model. Strains ofthe same ST and serotype therefore have important genetic and phenotypic differences