Amino acid substitution in the major multi-drug efflux transporter protein AcrB contributes to azithromycin low-susceptibility in Haemophilus influenzae [PublishAheadOfPrint]

Generally, clarithromycin-resistant Haemophilus influenzae with a nonsense mutation in acrR exhibited susceptibility to azithromycin, although one strain was found to be nonsusceptible. We aimed to clarify the differences. This strain had an amino acid substitution, Arg327Ser, in AcrB. Introduction of this substitution into H. influenzae Rd caused an increase in the MIC of azithromycin, suggesting that this substitution contributed to nonsusceptibility. These findings indicate that azithromycin-nonsusceptible isolates could occur by stepwise mutation in acr region.

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