Emi Tanaka1, Naoki Hara2, Takeaki Wajima3, Shoko Ochiai1, Shoji Seyama1, Atsuko Shirai4, Meiwa Shibata4, Hiroyuki Shiro4, Yoshiaki Natsume4, Norihisa Noguchi1. 1. Department of Microbiology, School of Pharmacy, Tokyo University of Pharmacy and Life Sciences, 1432-1 Horinouchi, Tokyo 192-0392, Japan. 2. Department of Microbiology, School of Pharmacy, Tokyo University of Pharmacy and Life Sciences, 1432-1 Horinouchi, Tokyo 192-0392, Japan; Japan Organization of Occupational Health and Safety, Yokohama Rosai Hospital, 3211 Kozukue, Kohoku, Yokohama, Kanagawa 222-0036, Japan. 3. Department of Microbiology, School of Pharmacy, Tokyo University of Pharmacy and Life Sciences, 1432-1 Horinouchi, Tokyo 192-0392, Japan. Electronic address: twajima@toyaku.ac.jp. 4. Japan Organization of Occupational Health and Safety, Yokohama Rosai Hospital, 3211 Kozukue, Kohoku, Yokohama, Kanagawa 222-0036, Japan.
Abstract
BACKGROUND: The use of non-β-lactam agents has increased in Japan due to the prevalence of β-lactam-resistant pathogens. This study aimed to clarify the recent trend of antimicrobial susceptibility and molecular epidemiological features in Haemophilus influenzae. METHODS: Fifty-seven Haemophilus influenzae isolated from a Japanese teaching hospital in 2017 were characterised, and the data were compared with those of a previous study. The MICs were determined using the broth dilution method. Genetic backgrounds were compared by multilocus sequence typing. The bactericidal activity of tosufloxacin at, or near, the therapeutic Cmax was determined in vitro, with susceptible isolates and quinolone low-susceptible isolates by time-kill assay. RESULTS: The results of the susceptibility tests showed that >90% of isolates were susceptible to cephalosporins and carbapenems, whereas ampicillin-susceptible and clarithromycin-susceptible isolates decreased. Regarding quinolones, low-susceptible isolates were noted in 2017, although all isolates were judged as susceptible. All low-susceptible isolates had an amino acid substitution in GyrA, and two isolates had an additional substitution in ParC. These isolates had different genetic backgrounds. Furthermore, the time-kill kinetic assay using the Cmax of tosufloxacin indicated that the low-susceptible isolates could persist for at least 8hours. CONCLUSIONS: This study revealed that Haemophilus influenzae has demonstrated multidrug low-susceptibility in recent years. The low-susceptible isolates had genetic diversity, meaning that resistance occurred independently.
BACKGROUND: The use of non-β-lactam agents has increased in Japan due to the prevalence of β-lactam-resistant pathogens. This study aimed to clarify the recent trend of antimicrobial susceptibility and molecular epidemiological features in Haemophilus influenzae. METHODS: Fifty-seven Haemophilus influenzae isolated from a Japanese teaching hospital in 2017 were characterised, and the data were compared with those of a previous study. The MICs were determined using the broth dilution method. Genetic backgrounds were compared by multilocus sequence typing. The bactericidal activity of tosufloxacin at, or near, the therapeutic Cmax was determined in vitro, with susceptible isolates and quinolone low-susceptible isolates by time-kill assay. RESULTS: The results of the susceptibility tests showed that >90% of isolates were susceptible to cephalosporins and carbapenems, whereas ampicillin-susceptible and clarithromycin-susceptible isolates decreased. Regarding quinolones, low-susceptible isolates were noted in 2017, although all isolates were judged as susceptible. All low-susceptible isolates had an amino acid substitution in GyrA, and two isolates had an additional substitution in ParC. These isolates had different genetic backgrounds. Furthermore, the time-kill kinetic assay using the Cmax of tosufloxacin indicated that the low-susceptible isolates could persist for at least 8hours. CONCLUSIONS: This study revealed that Haemophilus influenzae has demonstrated multidrug low-susceptibility in recent years. The low-susceptible isolates had genetic diversity, meaning that resistance occurred independently.