title: Molecular Epidemiology of Ampicillin-resistant Haemophilus influenzae Causing Acute Otitis Media in Japanese Infants and Young Children.
abstract: BACKGROUND
  Nontypeable Haemophilus influenzae is a particularly important cause of acute otitis media (AOM). There is a high prevalence of β-lactamase-nonproducing ampicillin-resistant (BLNAR) strains in Japanese children, which is associated with recurrent AOM and prolonged treatment. The aim of this study was to investigate the antimicrobial susceptibility profile, mechanisms of ampicillin resistance and molecular epidemiology of ampicillin resistance in H. influenzae strains causing AOM in Japanese children.
  
  
  METHODS
  One hundred fifty-seven strains of H. influenzae isolated from the middle ear fluid of pediatric patients (aged 0-3 years) with AOM from various areas of Japan were studied. The antimicrobial susceptibility profile, genes encoding β-lactamase and alterations of penicillin-binding protein 3 were investigated. Genetic relatedness among ampicillin-resistant isolates was examined by multilocus sequence typing and pulsed-field gel electrophoresis.
  
  
  RESULTS
  Of 157 isolates, 108 (68.8%) demonstrated reduced susceptibility to ampicillin, including 95 (60.5%) of β-lactamase-nonproducing isolates and 13 (8.3%) of β-lactamase-producing isolates. All BLNAR (minimum inhibitory concentration of ampicillin ≥ 4 mg/L) isolates had amino acid substitutions related to ampicillin resistance. Multilocus sequence typing and pulsed-field gel electrophoresis demonstrated genetic diversity although there were 2 clusters of highly resistant isolates with identical STs (sequence types; ST161 and 549).
  
  
  CONCLUSIONS
  Alterations of penicillin-binding protein 3 represented the most prevalent mechanism of ampicillin resistance among H. influenzae isolates causing AOM in Japanese children. BLNAR isolates from children with AOM demonstrated genetic diversity. This study identified for the first time ST clones associated with BLNAR H. influenzae causing AOM in Japanese children.
authors.affiliation: From the *Department of Otolaryngology, Head and Neck Surgery, Tohoku University Graduate School of Medicine, Sendai, Miyagi, Japan; †Department of Infection Control and Laboratory Diagnostics, Tohoku University Graduate School of Medicine, Sendai, Miyagi, Japan; ‡Department of Microbiology and Infectious Diseases, Nara Medical University, Kashihara, Nara, Japan; and §Department of Bacteriology, BML Inc., Kawagoe, Saitama, Japan.
authors.forename: Risako
authors.initials: R
authors.lastname: Kakuta
authors.forename: Hisakazu
authors.initials: H
authors.lastname: Yano
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Hidaka
authors.forename: Hajime
authors.initials: H
authors.lastname: Kanamori
authors.forename: Shiro
authors.initials: S
authors.lastname: Endo
authors.forename: Sadahiro
authors.initials: S
authors.lastname: Ichimura
authors.forename: Miho
authors.initials: M
authors.lastname: Ogawa
authors.forename: Masahiro
authors.initials: M
authors.lastname: Shimojima
authors.forename: Daiki
authors.initials: D
authors.lastname: Ozawa
authors.forename: Shinya
authors.initials: S
authors.lastname: Inomata
authors.forename: Ayako
authors.initials: A
authors.lastname: Tanouchi
authors.forename: Mitsuo
authors.initials: M
authors.lastname: Kaku
authors.forename: Yukio
authors.initials: Y
authors.lastname: Katori
mesh_terms: D000667:Ampicillin / Q000494:pharmacology*; D002675:Child, Preschool; D016521:Electrophoresis, Gel, Pulsed-Field; D005260:Female; D014644:Genetic Variation; D005838:Genotype; D006192:Haemophilus Infections / Q000453:epidemiology* / Q000382:microbiology; D006193:Haemophilus influenzae / Q000145:classification / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D007564:Japan / Q000453:epidemiology; D008297:Male; D008826:Microbial Sensitivity Tests; D017720:Molecular Epidemiology; D058885:Multilocus Sequence Typing; D010033:Otitis Media / Q000453:epidemiology* / Q000382:microbiology; D046915:Penicillin-Binding Proteins / Q000235:genetics; D018440:beta-Lactam Resistance; D001618:beta-Lactamases / Q000235:genetics
chemical_list: D046915:Penicillin-Binding Proteins; D000667:Ampicillin; D001618:beta-Lactamases