Antimicrobial susceptibility testing of historical and recent clinical isolates of Bordetella pertussis in the United Kingdom using the Etest method

Reports of the development of antimicrobial resistance by Bordetella pertussis to macrolides in the United States and Taiwan, together with a recent increase in pertussis notifications and laboratory-confirmed cases in England and Wales in 2008, prompted the examination of historical and recent clinical isolates from patients for evidence of such resistance in our collection. Isolates submitted to our laboratory as part of the enhanced surveillance scheme for pertussis, from 2001 to 2009, were tested against three agents, erythromycin, clarithromycin and azithromycin, by the Etest (bioMérieux) method. All isolates (n = 583) were fully susceptible to all three agents tested (minimum inhibitory concentrations [MICs] ≤0.125 µg/ml). All but one strain (582/583) had MICs of ≤0.064 for all three agents. The control strain of B. pertussis A228 (from the Centers for Disease Control and Prevention [CDC], Atlanta, Georgia, USA) with a resistant phenotype had an MIC of >256 µg/ml. Although no evidence of resistance was found in the strains tested from the United Kingdom, screening for antimicrobial resistance of B. pertussis may be warranted in cases that are unresponsive to macrolide treatment and to provide early warning of such emergence in the future.