Antimicrobial susceptibility and genetic characteristics of Haemophilus influenzae isolated from community-acquired respiratory tract infection patients in Shanghai City, China

Haemophilus influenzae is an important causative pathogen of community-acquired respiratory infection in China. In this study we investigated 37 H. influenzae strains isolated from patients with community-acquired respiratory tract infections (CARTI) in Shanghai city between Dec 2008 and Apr 2009. H. influenzae clinical isolates were identified, and β-lactamase production tests were conducted and minimal inhibitory concentrations (MIC) were measured. Pulsed-field gel electrophoresis (PFGE) was introduced as an effective fingerprinting method. Two isolates (5.4%) were verified as serotype b strains, and 30 strains (81.1%) were nontypeable H. influenzae. Furthermore, 10 (27.0%) were β-lactamase-producing ampicillin-resistance (BLPAR) (TEM-1 type) strains, 11 (29.8%) were low-β-lactamase-nonproducing ampicillin-resistant H. influenzae (Low-BLNAR) strains, and the rest were β-lactamase-negative ampicillin-susceptible (BLNAS) strains. Minimum inhibitory concentrations (MIC90; μg/ml) were 2 for ampicillin/sulbactam, 0.05 for cefotaxime, 16 for cefaclor, 2 for azithromycin, 0.12 for levofloxacin, and 4 for imipenem. Fingerprint typing by PFGE revealed 23 independent patterns for the isolates. Pattern A (defined in this study) was predominant in BLPAR strains, and a variety of other patterns were detected in Low-BLNAR and BLNAS strains. Although the incidence of ampicillin resistant H. influenzae is increasing in CARTI patients in China, current antimicrobial chemotherapy seems to be effective.