Affiliation:
1. Institut Pasteur, Unité des Agents Antibactériens, 75724 Paris Cedex 15, France
Abstract
ABSTRACT
Among
Acinetobacter
spp.,
A. baumannii
is the most frequently implicated in nosocomial infections, in particular in intensive care units. It was initially thought that multidrug resistance (MDR) in this species was due mainly to horizontal acquisition of resistance genes. However, it has recently become obvious that increased expression of chromosomal genes for efflux systems plays a major role in MDR. Among the five superfamilies of pumps, resistance-nodulation-division (RND) systems are the most prevalent in multiply resistant
A. baumannii
. RND pumps typically exhibit a wide substrate range that can include antibiotics, dyes, biocides, detergents, and antiseptics. Overexpression of AdeABC, secondary to mutations in the
adeRS
genes encoding a two-component regulatory system, constitutes a major mechanism of multiresistance in
A. baumannii
. AdeIJK, intrinsic to this species, is responsible for natural resistance, but since overexpression above a certain threshold is toxic for the host, its contribution to acquired resistance is minimal. The recently described AdeFGH, probably regulated by a LysR-type transcriptional regulator, also confers multidrug resistance when overexpressed. Non-RND efflux systems, such as CraA, AmvA, AbeM, and AbeS, have also been characterized for
A. baumannii
, as have AdeXYZ and AdeDE for other
Acinetobacter
spp. Finally, acquired narrow-spectrum efflux pumps, such as the major facilitator superfamily (MFS) members TetA, TetB, CmlA, and FloR and the small multidrug resistance (SMR) member QacE in
Acinetobacter
spp., have been detected and are mainly encoded by mobile genetic elements.
Publisher
American Society for Microbiology
Subject
Infectious Diseases,Pharmacology (medical),Pharmacology