Abstract
Acinetobacter baumannii is an important opportunistic nosocomial pathogen often resistant to multiple antibiotics classes. Colistin, an “old” antibiotic, is now considered a last-line treatment option for extremely resistant isolates. In the meantime, resistance to colistin has been reported in clinical A. baumannii strains. Colistin is a cationic peptide that disrupts the outer membrane (OM) of Gram-negative bacteria. Colistin resistance is primarily due to post-translational modification or loss of the lipopolysaccharide (LPS) molecules inserted into the outer leaflet of the OM. LPS modification prevents the binding of polymyxin to the bacterial surface and may lead to alterations in bacterial virulence. Antimicrobial pressure drives the evolution of antimicrobial resistance and resistance is often associated with a reduced bacterial fitness. Therefore, the alterations in LPS may induce changes in the fitness of A. baumannii. However, compensatory mutations in clinical A. baumannii may ameliorate the cost of resistance and may play an important role in the dissemination of colistin-resistant A. baumannii isolates. The focus of this review is to summarize the colistin resistance mechanisms, and understand their impact on the fitness and virulence of bacteria and on the dissemination of colistin-resistant A. baumannii strains.
Highlights
Acinetobacter baumannii is an opportunistic Gram-negative pathogen recognized worldwide as a significant concern
Colistin resistance is primarily due to post-translational modification or loss of the lipopolysaccharide (LPS) molecules inserted into the outer leaflet of the outer membrane (OM)
The purpose of this review is to summarize the resistance mechanisms of A. baumannii to colistin and to focus on the interplay of colistin resistance, virulence, and fitness cost of the bacteria to better understand the consequences of the mutations associated with colistin resistance and the biological response of the pathogen
Summary
Acinetobacter baumannii is an opportunistic Gram-negative pathogen recognized worldwide as a significant concern. The plasmidic colistin-resistance genes mcr-1 to -5 have been reported worldwide in Gram-negative bacteria from human, animal, and environmental samples [7,9,10,11,12,13,14], but not in. The number of cases of of polymyxin-resistant A. baumannii strains has been increasing worldwide [16], leading to a global concern on the treatment of these infections. The purpose of this review is to summarize the resistance mechanisms of A. baumannii to colistin and to focus on the interplay of colistin resistance, virulence, and fitness cost of the bacteria to better understand the consequences of the mutations associated with colistin resistance and the biological response of the pathogen
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