Relatedness of penicillin-resistant Streptococcus pneumoniae serogroup 9 strains from France and Spain.

Pulsed-field gel electrophoresis of the genomic DNA of penicillin-resistant strains of Streptococcus pneumoniae was carried out. Eleven clinical strains of serogroup 9 from different French towns and Paris hospitals were tested. The restriction enzymes Apal and Smal were used to digest intact chromosomes, and the fragments were resolved by field-inversion gel electrophoresis (FIGE). Five strains were similar using Apal and Smal. Four others were closely related when using Apal, and five others were closely related when using Smal. These results suggest that 10 of these strains are genetically related and have a clonal origin. The profile of the eleventh strain was completely different. Thus, in a given serotype the spreading of penicillin resistance can result from both clonal and independent events. Five strains had similar FIGE profiles to strains first isolated in Spain, suggesting that a resistant strain had spread from Spain to France.