Subtyping of common pediatric pneumococcal serotypes from invasive disease and pharyngeal carriage in Finland

Ninety-nine penicillin-sensitive Streptococcus pneumoniae strains of common pediatric sero-groups/types (6, 7, 14, 19, and 23) cultured from the blood of children with invasive disease (n = 49) or asymptomatic oropharyngeal carriage (n = 50) were analyzed by multilocus enzyme electrophoresis and ribotyping; 53 distinctive multilocus enzyme genotypes (ETs) and 53 ribotypes were identified. Multilocus enzyme electrophoresis showed good correlation with ribotyping. ETs and ribotypes among invasive and carriage isolates were similar. Within different S. pneumoniae serogroups/types, both clonal (7 and 14) and heterogenous (6, 19, and 23) ET and rRNA hybridization patterns were observed. Greatest diversity was observed among serotypes 6A, 6B, and 19F. Use of 12 additional restriction enzymes besides PvuII and BgIII did not increase ribotype discrimination within serotype 7 and 14 isolates. Serotype 7 and 14 strains, which appear clonal by subtyping, are rare among carriers but common causes of invasive disease. Characteristics associated with their clonality may represent an advantage for invasiveness.