Genetic alteration of penicillin non-susceptible Streptococcus pneumoniae observed throughout recurrence of acute otitis media detected by amplified fragment length polymorphism analysis

The prevalence of penicillin non-susceptible Streptococcus pneumoniae (PNSS P) is increasing among isolates from acute otitis media (AOM). Repeated epi sodes of antibiotic exposure are a well-known risk factor for the isolation of PNSSP although otitis-prone or recurrent AOM cases frequently require r epeated courses of antibiotic treatment. In order to evaluate the chronolog ical alteration of S. pneumoniae during recurrences of AOM, strains of S. p neumoniae were isolated from 11 patients, each of whom had experienced 2-4 episodes of AOM, were examined. Every bacterial specimen obtained from a si ngle episode of recurrent AOM was examined by PCR-based penicillin-binding protein (PBP) assay, serotyping, and amplified fragment length polymorphism (AFLP), then compared to other samples from the same case. Two cases (18.2 %) showed strain diversity during repeated antibiotic treatments by serotyp ing or PBP-assay. By AFLP analysis, 6 cases (54.5%) demonstrated heterogene ous strains during recurrent AOM. Clonal survivors of previous episodes of AOM were not always the cause of subsequent episodes of AOM, even in otitis -prone cases.