Mutation in crrB encoding a sensor kinase increases expression of the RND-type multidrug efflux pump KexD in Klebsiella pneumoniae

•A point mutation in a two-component regulatory system gene, crrB, was identified in mutants overexpressing KexD, an RND-type multidrug efflux pump, in Klebsiella pneumoniae.•Overexpression of CrrA changed the expression of kexD via crrB mutation.•Colistin resistance was not increased in our KexD-overexpressing mutants.