Genotypic survey of recent beta-lactam-resistant pneumococcal nasopharyngeal isolates from asymptomatic children in Chile

To assess pneumococcal strain variability among young asymptomatic carriers in Chile, we used serotyping, antibiotic susceptibility testing, and genot yping to analyze 68 multidrug-resistant pneumococcal isolates recovered fro m 54 asymptomatic children 6 to 48 months of age. The isolates represented capsular serotypes 19F (43 isolates), 14 (14 isolates), 23F (7 isolates), 6 B (3 isolates), and 6A (1 isolate). Genotypic analysis, which included puls ed-field gel electrophoresis (PFGE) of chromosomal digests, penicillin bind ing protein (PBP) gene fingerprinting, and dhf gene fingerprinting, reveale d that the isolates represented six different genetic lineages. Clear circu mstantial evidence of capsular switching was seen within each of four of th e genetically related sets. The majority of the isolates, consisting of the 43 19F isolates and 2 type 6B isolates, appeared to represent a geneticall y highly related set distinct from previously characterized pneumococcal st rains. Each of three other genetically defined lineages was closely related to one of the previously characterized clones Spain(6B)-2, France(9V)-3, o r Spain(23F)-1. A fifth lineage was comprised of four type 23F isolates tha t, by the techniques used for this study, were genetically indistinguishabl e from three recent type 19F sterile-site isolates from the United States. Finally, a sixth lineage was represented by a single type 23F isolate which had a unique PFGE type and unique PBP and dhf gene fingerprints.