Several Different Clones Present During the Penetration Phase of ResistantStreptococcus pneumoniaein the City of Malmö, Sweden

Abstract

A rapid increase in the prevalence of Streptococcus pneumoniae with reduced sensitivity to penicillin (MIC ≥0.12 μg/mL) was noted among clinical isolates during a 15-month period in 1994–1995 in the city of Malmö, Sweden. All first-time clinical isolates (n = 178) were consecutively collected and investigated for genetic relatedness with BOX-A PCR and arbitrarily primed (AP) PCR. An improved method for chromosomal DNA extraction and the use of three reliable discriminatory primers for AP-PCR of S. pneumoniae are described. Using molecular fingerprinting, 30 different genotypes were discerned among the 178 isolates. The majority (87%) of isolates belonged to serogroups 6,9,15,19, and 23. Resistance patterns and serogrouping indicated the presence of at least three major phenotypic clones. DNA fingerprinting in conjunction with minimum inhibitory concentration (MIC) values, resistance patterns, and epidemiological data confirmed the existence of two clones belonging to serogroups 6 and 9. Of the 178 isolates, 82% were from children of preschool age, most of whom attended day-care centers. We conclude that abundant S. pneumoniae strains with MICs ≥0.12 μg/mL for penicillin were present in the city of Malmö during the study period. At least two genetically discrete clones causing clinical illness were identified, and attendance at day-care centers may be a major factor in the spread of these strains.