Expression of the MexXY Aminoglycoside Efflux Pump and Presence of an Aminoglycoside-Modifying Enzyme in Clinical Pseudomonas aeruginosa Isolates Are Highly Correlated

Abstract

The impact of MexXY efflux pump expression on aminoglycoside resistance in clinical Pseudomonas aeruginosa isolates has been debated. In this study, we found that in general, elevated mexXY gene expression levels in clinical P. aeruginosa isolates confer to slight increases in aminoglycoside MIC levels, however those levels rarely lead to clinically relevant resistance phenotypes. The main driver of resistance in the clinical isolates studied here was the acquisition of aminoglycoside modifying enzymes (AMEs). Nevertheless, acquisition of an AME was strongly associated with mexY overexpression. In line with this observation, we demonstrate that the introduction of a gentamicin acetyl-transferase confers to full gentamicin resistance levels in a P. aeruginosa type strain only if the MexXY efflux pump was active. We discuss that increased mexXY activity in clinical AME harboring P. aeruginosa isolates might affect ion fluxes at the bacterial cell membrane and thus might play a role in the establishment of enhanced fitness that extends beyond aminoglycoside resistance.

The many antibiotic resistance and tolerance strategies of Pseudomonas aeruginosa

“…Aminoglycoside resistance through modifying enzymes which inactivate the aminoglycoside has been known to exist since the 1960's and 1970's [ [21] , [22] , [23] ]. These enzymes often phosphorylate or adenylate the antibiotics and multiple modifying enzymes are often harbored in a single genome, allowing for broad-spectrum antibiotic disruption [ [24] , [25] , [26] ]. In addition, modification of membrane permeability can lead to a decrease in the uptake of antibiotics [ 27 , 28 ], and, additionally, the presence of efflux pumps such as the MexXY pump (in aminoglycosides) or the MexCD-OprJ and MexEF-OprN pumps (in fluoroquinolones) serve to further prevent antibiotics from accumulating intracellularly [ 24 , [29] , [30] , [31] , [32] ].…”

“…These enzymes often phosphorylate or adenylate the antibiotics and multiple modifying enzymes are often harbored in a single genome, allowing for broad-spectrum antibiotic disruption [ [24] , [25] , [26] ]. In addition, modification of membrane permeability can lead to a decrease in the uptake of antibiotics [ 27 , 28 ], and, additionally, the presence of efflux pumps such as the MexXY pump (in aminoglycosides) or the MexCD-OprJ and MexEF-OprN pumps (in fluoroquinolones) serve to further prevent antibiotics from accumulating intracellularly [ 24 , [29] , [30] , [31] , [32] ]. Target site modification (ribosomal in the case of aminoglycosides, or DNA gyrase in fluoroquinolones) has also been noted, leading to a lack of binding of the antibiotic to its target [ 27 , 33 ].…”

“…A recent study on 60 P. aeruginosa strains isolated from burn patients found that 90% were resistant to at least one antibiotic and 94% of the isolates were multidrug resistant [ 25 ]. Another study on P. aeruginosa clinical isolates found overexpression of MexXY-OprM in 53% of strains, indicating the importance of efflux pumps as well in a clinical setting [ 24 ].…”

The Impact of an Efflux Pump Inhibitor on the Activity of Free and Liposomal Antibiotics against Pseudomonas aeruginosa

“…Regulates elastase, protease, exotoxin A, biofilm formation and induces PQS and Rhl systems [34,35] Protease Immune invasion and host tissue damage [7,29] MexXY-OprM Aminoglycosides, fluoroquinolones, tetracyclines and macrolides [22][23][24] RhlI/R (C 4 -HSL)…”

“…The main efflux systems with the highest clinical significance in P. aeruginosa are MexAB-OprM, MexCD-OprJ, MexEF-OprN, and MexXY-OprM pumps, which belong to the resistance nodulation cell division family and export metabolites, antibiotics and even quorum sensing (QS) molecules [15,19]. The MexAB-OprM pump transports beta-lactams, 2 of 18 macrolides, tetracyclines [20], and 3-oxo-dodecanoyl homoserine lactone (3OC 12 -HSL, QS signal) [21] among others, while the MexXY-OprM pump exports aminoglycosides, fluoroquinolones, tetracyclines and macrolides [22][23][24].…”