*4.3.2. Efflux systems*

Resistance to aminoglycosides in *P. aeruginosa* can occur independently of aminoglycosidemodifying enzymes in cystic fibrosis patients. This type of resistance has been reported in several studies [99,118-120] and is attributable to over-expression of the MexXY-OprM efflux pump.

## *4.3.3. 16S rRNA methylases*

Methylation of the 16S rRNA of the A site of the 30S ribosomal subunit interferes with aminoglycoside binding and consequently promotes high-level resistance to all aminoglyco‐ sides [24]. Different 16S rRNA methylases have been described for *P. aeruginosa*: RmtA [112,121], RmtB [122], ArmA [122,123] and RmtD which is commonly found together with the MBL SPM-1 in Brazil [124,125].
