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

Abstract

Conclusion. A high prevalence of penicillin-binding protein gene-mutated (PGM) strains of Haemophilus influenzae should be taken into account when treating otitis media in children. Objective. To evaluate the prevalence of β-lactamase-non-producing ampicillin-resistant strains of H. influenzae with mutations in the ftsI gene encoding penicillin-binding protein 3 (PBP3) among children with otitis media. Material and methods. A total of 644 nasopharyngeal isolates of H. influenzae were collected from pediatric acute otitis media patients with or without otitis media with effusion at the clinics of the Department of Otolaryngology—Head and Neck Surgery, Wakayama Medical University Hospital and 6 affiliated hospitals in Wakayama Prefecture between January 1999 and December 2003. MICs to ampicillin (AMP), cefdinir (CFD), cefaclor (CCL), cefpodoxime (CPD) and cefcapene (CFPN) were determined by a microbroth dilution method according to the recommendations of the National Committee for Clinical Laboratory Standards. Types of mutations in the PBP3 gene (ftsI) were evaluated by means of a polymerase chain reaction (PCR)-based genotyping method. The β-lactamase gene (bla) was also identified by means of PCR. Results. β-lactamase-producing (BLP) strains having the bla gene were identified in 16 isolates (2.5%). PGM strains were identified in 279 isolates (43.3%). There were 242 PGM1-non-BLP strains (37.6%) with mutations in the variable mutated locus of ftsI, 35 PGM2-non-BLP strains (5.4%) with mutations in the highly mutated locus of ftsI and 2 BLP-PGM strains (0.3%) with mutations in ftsI that produced β-lactamase. BLP-non-PGM strains producing β-lactamase without mutations in ftsI were identified in 14 isolates (2.2%). MICs of PGM1-non-BLP strains to AMP were 0.5–2.0 µg/ml. The MIC90 of CDN to the PGM1-non-BLP strains was the lowest (0.06 µg/ml). The proportion of PGM1-non-BLP strains increased rapidly during 1999–2002 and then decreased in 2003. In contrast, the proportion of PGM2-non-BLP strains increased in 2003.