Potentiation of Aminoglycoside Activity in Pseudomonas aeruginosa by Targeting the AmgRS Envelope Stress-Responsive Two-Component System

Abstract

A screen for agents that potentiated the activity of paromomycin (PAR), a 4,5-linked aminoglycoside (AG), against wild-type Pseudomonas aeruginosa identified the RNA polymerase inhibitor rifampin (RIF). RIF potentiated additional 4,5-linked AGs, such as neomycin and ribostamycin, but not the clinically important 4,6-linked AGs amikacin and gentamicin. Potentiation was absent in a mutant lacking the AmgRS envelope stress response two-component system (TCS), which protects the organism from AG-generated membrane-damaging aberrant polypeptides and, thus, promotes AG resistance, an indication that RIF was acting via this TCS in potentiating 4,5-linked AG activity. Potentiation was also absent in a RIF-resistant RNA polymerase mutant, consistent with its potentiation of AG activity being dependent on RNA polymerase perturbation. PAR-inducible expression of the AmgRS-dependent genes htpX and yccA was reduced by RIF, suggesting that AG activation of this TCS was compromised by this agent. Still, RIF did not compromise the membrane-protective activity of AmgRS, an indication that it impacted some other function of this TCS. RIF potentiated the activities of 4,5-linked AGs against several AG-resistant clinical isolates, in two cases also potentiating the activity of the 4,6-linked AGs. These cases were, in one instance, explained by an observed AmgRS-dependent expression of the MexXY multidrug efflux system, which accommodates a range of AGs, with RIF targeting of AmgRS undermining mexXY expression and its promotion of resistance to 4,5-and 4,6-linked AGs. Given this link between AmgRS, MexXY expression, and pan-AG resistance in P. aeruginosa, RIF might be a useful adjuvant in the AG treatment of P. aeruginosa infections. P seudomonas aeruginosa is a common nosocomial pathogen (1) and a major cause of morbidity and mortality in patients with cystic fibrosis (CF) (2, 3). Treatment of P. aeruginosa infections is complicated by the organism's innate resistance to many antimicrobials, a product of its impressive intrinsic resistome (4) and its access to an array of acquired resistance mechanisms (5, 6), with difficult-to-treat multidrug-resistant (MDR) (7) and extremely drug-resistant (8, 9) P. aeruginosa organisms becoming increasingly common. In the face of this intrinsic and acquired multidrug resistance, the use of agents historically used less commonly owing to issues of toxicity (e.g., the polymyxins) (10, 11) and the use of drug combination therapy (12, 13) are increasingly promoted. Still, despite much in vitro evidence for synergistic drug combinations being effective against MDR P. aeruginosa (14-20), the clinical benefits of drug combinations are less obvious (13,21,22).Aminoglycosides (AGs) have a long history in the management of P. aeruginosa infections, particularly in the case of lung infections in patients with cystic fibrosis (23,24), and are often used in combination with ␤-lactams (25-27) owing to a well-established synergy between these two antimicrobial classes (18,20,(26)(27)(28)(29). ␤-Lactam synergy ...

Multitarget Approaches against Multiresistant Superbugs

“…218 It was later found that the RNA polymerase inhibitor rifampicin was also a potent inhibitor of this stress response system and potentiated the activity of aminoglycosides like tobramycin, amikacin, gentamycin, and neomycin against P. aeruginosa. 219,220 A multitude of stress response systems have been identified that play a role for antibiotic adaptation and resistance, yet little effort has been put into identifying inhibitors of these systems to be used as antibiotic potentiators. In view of the urgent need for novel antibacterial strategies, this possibility deserves more attention.…”

Structure and mechanism of bacterial tripartite efflux pumps

“…Interestingly, in the case of bacitracin resistance in Bacillus subtilis, the bacitracin transporting ABC transporter BceAB acts as a sensor itself by mediating information on its transport activity, though protein-protein interaction, to the histidine kinase BceS [133]. Other examples for two component systems that regulate efflux pump expression include AmgRS in Pseudomonas aeruginosa, CpxAR in Enterobacteriaceae, and AdeSR in Acinetobacter baumannii [134]. In the latter case, AdeR (the response regulator) activates the expression of the adeABC tripartite system genes by binding to a direct-repeat motif in the intercistronic spacer [135].…”

Effect of Prodigiosin on Biofilm Formation in Clinical Isolates of Pseudomonas Aeruginosa

“…The handling of infections of P. aeruginosa keep to be an important challenge. Resistance of P. aeruginosais to antibiotic is multi-factorial, in that it can occur through acquired, innate or adaptive mechanisms (Poole et al, 2016).…”