Prevalence of pilus-encoding islets and clonality of pneumococcal isolates from children with acute otitis media.

We characterized the prevalence of pilus islets 1 (PI-1) and 2 (PI-2) and the clonality of Streptococcus pneumoniae isolates taken from children with acute otitis media (AOM) to study the association between pilus existence and AOM disease potential prior to pneumococcal conjugate vaccine and increased antimicrobial resistance. The study material consisted of 75 pneumococcal isolates cultured from the middle ear fluid and/or nasopharyngeal aspirate of 56 children with AOM in Finland during the period 1990-1992. Isolates were studied for antimicrobial susceptibility and were serotyped, genotyped by multilocus sequence typing (MLST), and tested for the presence of pneumococcal PI-1 and PI-2 genes. All isolates were susceptible to penicillin, 14 different serotypes were found, and 20% of the isolates were positive for PI-1 genes. PI-2 genes were not found. MLST showed high heterogeneity: 52 AOM isolates belonged to 18 known clonal complexes (CC). PI-1 was associated with serotypes 6A, 6B, and 9V, and genotype CC490. In the time prior to 7-valent pneumococcal conjugate vaccine (PCV7) and increased antimicrobial resistance, pneumococcal AOM isolates carried PI-1 genes at a rather low prevalence. PI-2 genes were not detected. PI-1 was related to serotype rather than genotype. The importance of PI-1 in AOM infections and its association with the spread of antimicrobial resistance requires further research.