Resistance profiles of Haemophilus influenzae and Haemophilus parainfluenzae isolates in Shanghai / 中华传染病杂志

ABSTRACT

Objective. To understand drug susceptibilities to common antibacterials, resistance mechanism to β-lactams and quinolones and the clonal spread of resistant stains of Haemophilus influenzae (H. influenzae) and Haernophilus parainfluenzae (H. parainfluenzae) isolated from some hospitals in Shanghai. Methods The in vitro antimicrobial susceptibilities to 13 antibacterials, such as ampicillin, of 156 Haemophilus strains collected from 5 hospitals of Shanghai in 2006 were tested by agar dilution method. The β-lactamase production was determined by chromogenic cephalosporin test. TEM and ROB type of β-lactamase genes and quinolone resistance determining regions (QRDR) of ciprofloxacin-resistant strains were detected by polymerase chain reaction (PCR) amplification. The homology of H. influenzae strains were analyzed by enterobacterial repetitive intergenic consensus (ERIC)-PCR. Results The susceptible rate of 109 strains H. influenzae to ampicillin was 74.3%, while those to ampicillin-sulbactam, cephatosporins and fluoroquinolones were all 100.0%. The β-lactamases-producing rates of 109 strains H. influenzae and 47 strains H. parainfluenzae were 25.7% and 19.1% (χ2=0.776,P=0.378), respectively. TEM gene was detected in all β-lactamases-producing strains. Of 109 H. influenzae isolates, only one was resistant to ciprofloxacin, and Ser84Leu mutation was detected in gyrA gene and Gly206Arg mutation in parC gene. The results of ERIC-PCR showed that 106 H. influenzae strains were clustered into 73 groups with similarity level of 85%. Conclusions Clinical isolates of H. influenzae from hospitals in Shanghai remain highly susceptible to common antimicrobial agents except ampicillin. TEM type of β-lactamase production is the main ampicillin-resistant mechanism of the tested stains. The clonal spread of H. influenzae, including ampicillin-resistant strains, is not prevalent.