β-Lactamase-non-producing ampicillin-resistant Haemophilus influenzae is acquiring multidrug resistance

Abstract

Background: Haemophilus influenzae strains with reduced susceptibilities to antimicrobial agents have emerged in Japan. Here, we aimed to investigate H. influenzae non-susceptibility to β-lactams and non-β-lactams. Methods: A total of 260 H. influenzae isolates from patients in 2013–2016 were analysed. Antimicrobial susceptibilities were assessed by determining the minimum inhibitory concentration. Additionally, isolates with reduced susceptibility were analysed by both genetic and statistical methods. Results: β-Lactamase-non-producing ampicillin-resistant H. influenzae (BLNAR) strains increased significantly and accounted for more than 50% of all isolates from 2014. Additionally, the proportion of quinolone-low-susceptibility isolates increased significantly (P < 0.05). Among these, three quinolone-non-susceptible isolates showed minimum inhibitory concentrations higher than the susceptibility breakpoint of levofloxacin. Moreover, one of the three isolates showing multidrug resistance was resistant to macrolides, β-lactams, and quinolones. Low susceptibilities to non-β-lactams were significantly associated with BLNAR. Conclusions: The present study indicates that BLNAR strains are increasing and tend to show multidrug resistance. Additionally, multidrug-resistant H. influenzae (MDRHI) has emerged. To prevent the further spread of MDRHI, the proportions of BLNAR strains should be evaluated. Keywords: Macrolide, Fluoroquinolone, Antimicrobial susceptibility, Multidrug-resistant Haemophilus influenzae