title: Prevalence of macrolide-non-susceptible isolates among β-lactamase-negative ampicillin-resistant Haemophilus influenzae in a tertiary care hospital in Japan.
abstract: β-Lactamase-negative ampicillin-resistant (BLNAR) Haemophilus influenzae account for a large portion of H. influenzae clinical isolates in Japan. The aim of this study was to clarify the antimicrobial susceptibility of BLNAR H. influenzae clinical isolates as well as the annual changes in susceptibility. BLNAR H. influenzae isolates were collected from a tertiary care hospital from 2007 to 2012. Antimicrobial susceptibility testing was performed and resistance mechanisms were analysed. All of the isolates (n=304) had amino acid substitutions in penicillin-binding protein 3 (PBP3) and isolates were classified by these amino acid substitutions: R517H or N526K (class I); S385T and R517H (class II); and S385T and N526K (class III). Classes I, II and III represented 8.2% (n=25), 9.5% (n=29) and 81.6% (n=248) of the isolates, respectively; 2 isolates could not be classified because they had a PBP3 with a substantially mutated FtsI transpeptidase domain. All of the isolates were highly susceptible to fluoroquinolones and carbapenems. The number of clarithromycin (CAM)-non-susceptible [minimum inhibitory concentration (MIC) ≥16μg/mL] H. influenzae isolates increased significantly between 2010 and 2012. Moreover, CAM-non-susceptible H. influenzae isolates were prevalent among class II and class III BLNAR H. influenzae. Multilocus sequence typing (MLST) of the CAM-resistant (MIC ≥32μg/mL) H. influenzae isolates showed that they were not specific sequence types, suggesting that CAM resistance may occur in any isolates. These results raise concern regarding the occurrence of multidrug-resistant BLNAR H. influenzae.
authors.affiliation: Department of Microbiology, School of Pharmacy, Tokyo University of Pharmacy and Life Sciences, 1432-1 Horinouchi, Hachioji, Tokyo 192-0392, Japan.
authors.forename: Takeaki
authors.initials: T
authors.lastname: Wajima
authors.affiliation: Department of Microbiology, School of Pharmacy, Tokyo University of Pharmacy and Life Sciences, 1432-1 Horinouchi, Hachioji, Tokyo 192-0392, Japan.
authors.forename: Shoji
authors.initials: S
authors.lastname: Seyama
authors.affiliation: Department of Microbiology, School of Pharmacy, Tokyo University of Pharmacy and Life Sciences, 1432-1 Horinouchi, Hachioji, Tokyo 192-0392, Japan.
authors.forename: Yuka
authors.initials: Y
authors.lastname: Nakamura
authors.affiliation: Department of Microbiology, School of Pharmacy, Tokyo University of Pharmacy and Life Sciences, 1432-1 Horinouchi, Hachioji, Tokyo 192-0392, Japan.
authors.forename: Chihiro
authors.initials: C
authors.lastname: Kashima
authors.affiliation: Department of Microbiology, School of Pharmacy, Tokyo University of Pharmacy and Life Sciences, 1432-1 Horinouchi, Hachioji, Tokyo 192-0392, Japan.
authors.forename: Hidemasa
authors.initials: H
authors.lastname: Nakaminami
authors.affiliation: Department of Pediatrics, Hachioji Medical Center, Tokyo Medical University, Tokyo, Japan.
authors.forename: Masanobu
authors.initials: M
authors.lastname: Ushio
authors.affiliation: Department of Infectious Diseases, Hachioji Medical Center, Tokyo Medical University, Tokyo, Japan.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Fujii
authors.affiliation: Department of Microbiology, School of Pharmacy, Tokyo University of Pharmacy and Life Sciences, 1432-1 Horinouchi, Hachioji, Tokyo 192-0392, Japan. Electronic address: noguchin@toyaku.ac.jp.
authors.forename: Norihisa
authors.initials: N
authors.lastname: Noguchi
mesh_terms: D019943:Amino Acid Substitution; D000667:Ampicillin; D015373:Bacterial Typing Techniques; D024901:Drug Resistance, Multiple, Bacterial; D006192:Haemophilus Infections / Q000453:epidemiology / Q000382:microbiology*; D006193:Haemophilus influenzae / Q000145:classification / Q000187:drug effects* / Q000302:isolation & purification; D006801:Humans; D007564:Japan / Q000453:epidemiology; D018942:Macrolides / Q000494:pharmacology*; D008826:Microbial Sensitivity Tests; D058885:Multilocus Sequence Typing; D015995:Prevalence; D062606:Tertiary Care Centers; D001618:beta-Lactamases
chemical_list: D018942:Macrolides; D000667:Ampicillin; D001618:beta-Lactamases
keywords: BLNAR Haemophilus influenzae; Macrolide resistance; PBP3