Objective To understand the susceptibility of Bordetella pertussis to antibiotics and variation of drug resistance sites of the isolates in Tianjin and provide evidence for pertussis prevention and treatment.

Methods A total of 18 strains of B. pertussis were isolated in Tianjin from February 2012 to July 2017. The susceptibilities of B. pertussis isolates to erythromycin, azithromycin, clarithromycin, levofloxacin and clindamycin were detected with disk diffusion method, and the susceptibilities of the isolates to erythromycin, azithromycin, clarithromycin, levofloxacin and sulphamethoxazole/trimethoprim were detected with E-test method. A fragment of domain V in the 23S rRNA as binding region to erythromycin was amplified and sequenced.

Results The results of disk diffusion showed that only one of the 18 isolates was sensitive to all the tested antibiotics, the remaining 17 isolates were resistant to erythromycin, azithromycin, clarithromycin and clindamycin, the resistant rate to erythromycin was highest (94.44 %, 17/18), and all the 18 isolates were sensitive to levofloxacin; E-test showed that only one isolate was sensitive to erythromycin, azithromycin and clarithromycin indicated by minimum inhibitory concentration (MIC) test. The MICs of all the tested antibiotics to the remaining 17 isolates were ＞ 256 μg/ml. The MICs of levofloxacin to the 18 isolates were 0.19–0.38 μg/ml and those of sulphamethoxazole/trimethoprim were 0.047–1.500 μg/ml. PCR amplification of the 23S rRNA region found that 17 antibiotic resistant isolates had A2047G mutation.

Conclusion The disk diffusion method and E-test method were used to detect the drug resistance of B. pertussis isolates in Tianjin. The coincidence rate of the two methods for erythromycin, azithromycin, clarithromycin and levofloxacin was 100%. Seventeen isolates were resistant to erythromycin, azithromycin and clarithromycin at the same time. All the antibiotic resistant isolates showed A2047G mutation in the 23S rRNA region.