Antimicrobial resistance in Haemophilus influenzae isolated from the nasopharynx among Japanese children with acute otitis media

Conclusion. High prevalence of penicillin-binding protein (PBP) gene mutated (PGM) strains of H. influenzae should be taken into account when treating otitis media in children. Objective. To evaluate prevalence of beta-lactamase nonproducing ampicillin-resistant (BLNAR) strains of Haemophilus influenzae with mutations in ftsI gene encoding penicillin-binding protein 3 (PBP3) among children with otitis media. Methods. A total of 644 nasopharyngeal isolates of H. influenzae was collected from pediatric acute otitis media (AOM) patients with or without otitis media with effusions (OME) at the clinics of Otolaryngology-Head and Neck Surgery, Wakayama Medical University Hospital and six affiliated hospitals in Wakayama prefecture between January 1999 and December 2003. Minimal inhibitory concentrations (MICs) of ampicillin ( AMP), cefditoren (CDN), cefdinir (CFD), cefaclor (CCL), cefpodoxime (CPD), and cefcapene (CFPN) were determined by the microbroth dilution method according to the recommendations of the National Committee for Clinical Laboratory Standards (NCCLS). Types of mutations in PBP3 gene ( ftsI) were evaluated by a polymerase chain reaction (PCR)-based genotyping method. beta-Lactamase gene (bla) was also identified by PCR. Results. beta-Lactamase-producing (BLP) strains with the bla gene were identified in 16 (2.5%) of isolates. PGM strains were identified in 279 (43.3%) isolates. There were 242 (37.6%) PGM1-nonBLP strains with mutations in variable mutated locus of ftsI, 35 (5.4%) PGM2-nonBLP strains with mutations in highly mutated locus of ftsI, 2 (0.3%) BLP-PGM strains with mutations in ftsI and producing beta-lactamase. BLP-nonPGM strains producing beta-lactamase without mutations in ftsI were identified in 14 (2.2%) isolates. MICs of PGM1-nonBLP strains to AMP were 0.5 - 2.0 mu g/ml. The MIC90 of CDN to the PGM1-nonBLP strains was lowest (0.06 mu g/ml). Proportions of PGM1-nonBLP strains rapidly increased during 1999 to 2002 and then decreased in 2003. In contrast, PGM2-nonBLP strains increased in 2003.