Role of Pseudomonas aeruginosa AmpR on β-lactam and non-β-lactam transient cross-resistance upon pre-exposure to subinhibitory concentrations of antibiotics.
Pseudomonas aeruginosa is one of the most dreaded opportunistic pathogens accounting for 10 % of hospital-acquired infections, with a 50 % mortality rate in chronically ill patients. The increased prevalence of drug-resistant isolates is a major cause of concern. Resistance in P. aeruginosa is mediated by various mechanisms, some of which are shared among different classes of antibiotics and which raise the possibility of cross-resistance. The goal of this study was to explore the effect of subinhibitory concentrations (SICs) of clinically relevant antibiotics and the role of a global antibiotic resistance and virulence regulator, AmpR, in developing cross-resistance. We investigated the induction of transient cross-resistance in P. aeruginosa PAO1 upon exposure to SICs of antibiotics. Pre-exposure to carbapenems, specifically imipenem, even at 3 ng ml(-1), adversely affected the efficacy of clinically used penicillins and cephalosporins. The high β-lactam resistance was due to elevated expression of both ampC and ampR, encoding a chromosomal β-lactamase and its regulator, respectively. Differences in the susceptibility of ampR and ampC mutants suggested non-AmpC-mediated regulation of β-lactam resistance by AmpR. The increased susceptibility of P. aeruginosa in the absence of ampR to various antibiotics upon SIC exposure suggests that AmpR plays a major role in the cross-resistance. AmpR was shown previously to be involved in resistance to quinolones by regulating MexEF-OprN efflux pump. The data here further indicate the role of AmpR in cross-resistance between quinolones and aminoglycosides. This was confirmed using quantitative PCR, where expression of the mexEF efflux pump was further induced by ciprofloxacin and tobramycin, its substrate and a non-substrate, respectively, in the absence of ampR. The data presented here highlight the intricate cross-regulation of antibiotic resistance pathways at SICs of antibiotics and the need for careful assessment of the order of antibiotic regimens as this may have dire consequences. Targeting a global regulator such as AmpR that connects diverse pathways is a feasible therapeutic approach to combat P. aeruginosa pathogenesis.
Department of Molecular Genetics, Herbert Wertheim College of Medicine, Florida International University, Miami, FL, USA.
Hansi
H
Kumari
Department of Biological Sciences, College of Arts and Sciences, Florida International University, Miami, FL, USA.|Department of Molecular Genetics, Herbert Wertheim College of Medicine, Florida International University, Miami, FL, USA.
Deepak
D
Balasubramanian
Department of Biological Sciences, College of Arts and Sciences, Florida International University, Miami, FL, USA.|Department of Molecular Genetics, Herbert Wertheim College of Medicine, Florida International University, Miami, FL, USA.
Diansy
D
Zincke
Department of Molecular Genetics, Herbert Wertheim College of Medicine, Florida International University, Miami, FL, USA.
Kalai
K
Mathee
D000617:Aminoglycosides / Q000378:metabolism; D000900:Anti-Bacterial Agents / Q000378:metabolism*; D001426:Bacterial Proteins / Q000378:metabolism*; D011550:Pseudomonas aeruginosa / Q000187:drug effects*; D015363:Quinolones / Q000378:metabolism; D015533:Transcriptional Activation; D018440:beta-Lactam Resistance; D047090:beta-Lactams / Q000378:metabolism*
D000617:Aminoglycosides; D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D015363:Quinolones; D047090:beta-Lactams; C071526:AmpR protein, Bacteria