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 b-lactamase production tests were conducted and minimal inhibitory concentrations(MIC) were measured. Pulsed-field gel electrophoresis(PFGE) was introduced as an effective finger printing 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 b-lactamase-producing ampicillin-resistance (BLPAR) (TEM-1 type)strains, 11 (29.8%) were low-b-lactamase-nonproducing ampicillin-resistant H. influenzae (Low-BLNAR) strains,and the rest were b-lactamase-negative ampicillin-susceptible(BLNAS) strains. Minimum inhibitory concentrations(MIC90; lg/ml) were 2 for ampicillin/sulbactam, 0.05 force fotaxime, 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.