[Multi-drug resistant Pseudomonas aeruginosa: towards a therapeutic dead end?].

Pseudomonas aeruginosa is a major hospital-associated pathogen that can cause severe infections, most notably in patients with cystic fibrosis or those hospitalized in intensive care units. In this context, the current increase in incidence of multi-drug resistant (MDR) isolates of P. aeruginosa (MDRPA) raises serious concerns. MDR in P. aeruginosa is defined as the resistance to 3 or 4 of the following antibiotic classes: penicillins/cephalosporins/monobactams, carbapenems, aminoglycosides, and fluoroquinolones. These strains constantly cumulate several resistance mechanisms as a consequence of multiple genetic events, i.e., chromosomal mutations or horizontal transfers of resistance genes. Involved mechanisms may include active efflux, impermeability resulting from porins loss, plasmid-encoded b-lactamases/carbapenemases or aminoglycosides-modifying enzymes, and enzymatic or mutation-associated changes in antibiotics targets. Antibiotic selection pressure represents the leading risk factor for MDRPA acquisition. Colistin (polymyxin E) remains active on virtually all MDRPA isolates, and increasingly appears as the last available option to treat infections caused by these strains. However, the emergence of colistin resistance has been reported in P. aeruginosa, which may announce the spread of pan-resistant strains in a close future.