Resistance-Nodulation-Cell Division-Type Efflux Pump Involved in Aminoglycoside Resistance in <i>Acinetobacter baumannii</i> Strain BM4454

TLDR

Multidrug‑resistant Acinetobacter baumannii BM4454, isolated from a urinary tract infection, harbors an adeABC efflux cluster whose regulation may involve upstream two‑component system genes. The adeB gene, encoding an RND efflux protein, was identified in BM4454 by PCR using degenerate primers. Inactivation of adeB abolished aminoglycoside resistance and altered susceptibility to several other antibiotics, and ethidium bromide accumulation studies revealed that AdeB decreases intracellular dye levels via a proton‑motive‑force‑dependent mechanism.

Abstract

ABSTRACT Multidrug-resistant strain Acinetobacter baumannii BM4454 was isolated from a patient with a urinary tract infection. The adeB gene, which encodes a resistance-nodulation-cell division (RND) protein, was detected in this strain by PCR with two degenerate oligodeoxynucleotides. Insertional inactivation of adeB in BM4454, which generated BM4454-1, showed that the corresponding protein was responsible for aminoglycoside resistance and was involved in the level of susceptibility to other drugs including fluoroquinolones, tetracyclines, chloramphenicol, erythromycin, trimethoprim, and ethidium bromide. Study of ethidium bromide accumulation in BM4454 and BM4454-1, in the presence or in the absence of carbonyl cyanide m -chlorophenylhydrazone, demonstrated that AdeB was responsible for the decrease in intracellular ethidium 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 homologous to membrane fusion and outer membrane proteins of RND-type three-component efflux systems, respectively. The products of two upstream open reading frames encoding a putative two-component regulatory system might be involved in the regulation of expression of the adeABC gene cluster.