Diversity of penicillin-nonsusceptible Streptococcus pneumoniae circulating in Iceland after the introduction of penicillin-resistant clone Spain(6B)-2.

After the introduction and extensive dissemination of the multidrug-resistant Streptococcus pneumoniae clone Spain(6B)-2 between 1989 and the early to mid-1990s, the prevalence of pneumococcal isolates expressing intermediate resistance to penicillin, mainly of capsular types 6, 19, and 23, also began to increase in Iceland. The purpose of this study was to investigate whether these isolates originated in Iceland or represented strains imported to the country. Isolates were characterized by pulsed-field gel electrophoresis; multilocus sequence typing; determination of pbp1a, pbp2b, and pbp2x gene restriction patterns; and partial sequencing of these pbp genes. The results indicate that, although singular events suggesting horizontal transfer of pbp genes (and capsular genes) were detected, the majority of clones circulating in the country had genetic backgrounds also detected abroad. The major mechanism of dissemination of penicillin resistance in Iceland appears to be the repeated introduction of multiple lineages, followed by clonal spread.