An internationally spread clone of Streptococcus pneumoniae evolves from low-level to higher-level penicillin resistance by uptake of penicillin-binding protein gene fragments from nonencapsulated pneumococci.

Low-level penicillin resistance in an international Streptococcus pneumoniae serotype 19F clone emerging in Switzerland was characterized by mutations in the penicillin-binding protein PBP2x. Some isolates of this clone had evolved to higher resistance levels (penicillin MICs of 0.094 and 1 microg/ml), probably by acquisition of pbp2x fragments from local nonencapsulated pneumococci.