Multidrug efflux pump that functions probably as a Na(+)/drug antiporter. Belongs to the multi antimicrobial extrusion (MATE) (TC 2.A.66.1) family. MdtK subfamily. PubMed:12384590 (AE005674) sequence differs from that shown due to the presence of an insertion sequence. In strain 301, this gene is probably a pseudogene.