The rise and fall of bacterial clones: Streptococcus pneumoniae

Globally spreading bacterial strains belong to clonal types that have the capacity to colonize, spread and cause disease in the community. Recent comparative genomic analyses of well-defined clinical isolates have led to the identification of bacterial properties that are required for the successful spread of bacterial clones. In this Review, we discuss the evolution of bacterial clones, the importance of recombination versus mutations for evolution of clones, common methods used to study clonal relationships among bacteria, factors that may contribute to the clonal spread of bacteria and the potential relevance of bacterial clones to clinical disease. We focus on the common pathogen Streptococcus pneumoniae, although other bacteria are also briefly discussed, such as Helicobacter pylori, Staphylococcus aureus and Mycobacterium tuberculosis.