2017 Volume 70 Issue 2 Pages 97-117
We investigated the susceptibility to antibacterial agents of 175 strains of Haemophilus influenzae isolated at medical facilities in Gifu, Aichi, Toyama and Fukui prefectures between 2014 and 2015. Those strains were also examined for the mutations of ftsI coding for penicillin-binding protein 3, presence of bla TEM-1, serotype and β-lactamase producing ability.
Among the 175 strains, 93 strains (53.1%) were isolated from adult patients and 82 strains (46.9%) were isolated from pediatric patients, and 86 strains (49.1%) were derived from sputum, 57 strains (32.6%) were derived from the pharynx and 21 strains (12.0%) were derived from nasal discharge or the nasal cavity. The MIC90s of antibacterial agents against the 175 strains were as follows; 0.0156 µg/mL for tosufloxacin, 0.0313 µg/mL for garenoxacin, levofloxacin and pazufloxacin, 0.0625 µg/mL for moxifloxacin, 0.125 µg/mL for tazobactam/piperacillin, 0.25 µg/mL for ceftriaxone, 0.5 µg/mL for meropenem, minocycline and cefditoren, 1 µg/mL for tebipenem and cefteram, 2 µg/mL for cefotaxime and azithromycin, 4 µg/mL for piperacillin, 8 µg/mL for sulbactam/ampicillin, 16 µg/ mL for amoxicillin, clavulanic acid/amoxicillin (1:2 and 1:14), ampicillin, cefdinir and clarithromycin.
Based on the susceptibility among the 175 strains to antibacterial agents, β-lactamase non- producing ampicillin-susceptible H. influenzae (BLNAS) accounted for 47 strains (26.9%), β-lactamase non-producing ampicillin-intermediately resistant H. influenzae (BLNAI) accounted for 31 strains (17.7%), β-lactamase non-producing ampicillin-resistant H. influenzae (BLNAR) for 72 strains (41.1%), β-lactamase producing ampicillin-resistant H. influenzae (BLPAR) for 17 strains (9.7%) and β-lactamase producing amoxicillin/clavulanic acid-resistant H. influenzae (BLPACR) for 8 strains( 4.6%).
According to PCR-based genotyping, the strains were classified as 29 strains (16.6%) for gBLNAS, 7 strains (4.0%) for gLow-BLNAR, 114 strains (65.1%) for gBLNAR, 13 strains (7.4%) for gBLPAR, 1 strain (0.6%) for gBLPACR-I and 11 strains (6.3%) for gBLPACR-II.
Among the 82 strains isolated from pediatric patients, the most prevalent serotype was non-typeable (79 strains, 96.3%), followed by serotype f (2 strains, 2.4%) and b (1 strain, 1.2%).
In this study, the ratio of H. influenzae type b (Hib) isolated from pediatric patients was decreased compared with the previous study. It was seemed to be affected that Hib was added to routine vaccination from 2013.
Although the susceptibilities to antibacterial agents were not that different to the previous study and the increasing trend of BLNAR was no longer observed, the ratio of BLNAR remains high. We have periodically reported local surveillance of antimicrobial susceptibility of H. influenzae. Moreover, in order to ensure the appropriate antibiotic use, it is important to continue the local surveillance of antimicrobial susceptibility.
