Resistance-nodulation-cell division-type efflux pump involved in aminoglycoside resistance in Acinetobacter baumannii strain BM4454

Multidrug-resistant strain Acinetobacter baumannii BM4454 was isolated from a patient with a urinary tract infection. The adeB gene, which encodes a r esistance-nodulation-cell division (RND) protein, was detected in this stra in by PCR with two degenerate oligodeoxynucleotides. Insertional inactivati on of adeB in BM4454, which generated BM4454-1, showed that the correspondi ng protein was responsible for aminoglycoside resistance and was involved i n the level of susceptibility to other drugs including fluoroquinolones, te tracyclines, chloramphenicol, erythromycin, trimethoprim, and ethidium brom ide. Study of ethidium bromide accumulation in BM4454 and BM4454-1, in the presence or in the absence of carbonyl cyanide m-chlorophenylhydrazone, dem onstrated that AdeB was responsible for the decrease in intracellular ethid ium bromide levels in a proton motive force-dependent manner. The adeB gene was part of a cluster that included adeA and adeC which encodes proteins h omologous to membrane fusion and outer membrane proteins of RND-type three- component efflux systems, respectively. The products of two upstream open r eading frames encoding a putative two-component regulatory system might be involved in the regulation of expression of the adeABC gene cluster.