Multilocus sequence typing of Streptococcus pneumoniae clones with unusualdrug resistance patterns: Genetic backgrounds and relatedness to other epidemic clones

Six drug-resistant Streptococcus pneumoniae clones were previously identifi ed from day care centers in Portugal, primarily on the basis of common puls ed-field gel electrophoresis (PFGE) patterns. These clones were susceptible to penicillin or had only very low-level resistance to it (most MICs, less than or equal to0.25 mug/mL) and accounted for a large proportion (35%) of all drug-resistant pneumococci colonizing the nasopharynx of healthy child ren attending day care. Five of the 6 clones were identified among pneumoco ccal clinical isolates collected in other countries. In this study, we appl ied multilocus sequence typing (MLST) to describe the genetic background of these clones. MLST confirmed previous findings obtained by PFGE and allowe d for the extension of the international clonal relationships by showing th at each of the 6 clones was internationally disseminated and was able to ca use pneumococcal disease.