Antimicrobial susceptibility of respiratory Haemophilus influenzae strains isolated from pediatric respiratory tract infections

Abstract Background : Haemophilus influenzae (H. influenzae) is the most frequent bacterial pathogen of respiratory tract infections in children. Detection of antimicrobial susceptibility of H. influenzae is necessary for institution of appropriate antibiotic treatments. Methods : A total of 281 strains of H. influenzae isolated from sputum samples of 281 pediatric patients with respiratory tract infections were recruited for study. Antibiotic susceptibility was determined by assessing minimum inhibitory concentrations (MIC) of antimicrobial agents. MIC were measured by utility of Agar dilution susceptibility test. Results : Of the total, 38 (13.5%) strains produced β‐lactamase (BLP), 56 (19.9%) strains were β‐lactamase non‐producing, ampicillin resistant (BLNAR). The overall resistant proportion to ampicillin was 33.4%. The data indicated that sulbactam/ampicillin, cefotaxime, ceftriaxone and cefditoren are effective against BLP strains. In addition, a high prevalence of BLNAR H. influenzae strains was identified, with an overall isolation rate of 19.9%. Those strains mainly demonstrated intermediate level to ampicillin (ampicillin‐MIC ≤ 3.13 µg/mL for most of BLNAR strains). However, antimicrobial activities of cefotaxime, ceftriaxone and cefditoren against those strains were slightly diminished. Recovery rate of BLP strains was varied by years, peaking at 19.5%. In particular, a trend of yearly increase in frequency of BLNAR strains was observed. Conclusion : Frequency of BLNAR strains causing respiratory infections has been dramatically increasing, which can diminish antibiotic activities of not only ampicillin but also of some cephems.