Novel Polymyxin Combination With Antineoplastic Mitotane Improved the Bacterial Killing Against Polymyxin-Resistant Multidrug-Resistant Gram-Negative Pathogens.

Thien B Tran,Yohei Doi,Tony Velkov,Jiping Wang,Phillip J Bergen,Jian Li

doi:10.3389/fmicb.2018.00721

Abstract

Due to limited new antibiotics, polymyxins are increasingly used to treat multidrug-resistant (MDR) Gram-negative bacteria, in particular carbapenem-resistant Acinetobacter baumannii, Pseudomonas aeruginosa, and Klebsiella pneumoniae. Unfortunately, polymyxin monotherapy has led to the emergence of resistance. Polymyxin combination therapy has been demonstrated to improve bacterial killing and prevent the emergence of resistance. From a preliminary screening of an FDA drug library, we identified antineoplastic mitotane as a potential candidate for combination therapy with polymyxin B against polymyxin-resistant Gram-negative bacteria. Here, we demonstrated that the combination of polymyxin B with mitotane enhances the in vitro antimicrobial activity of polymyxin B against 10 strains of A. baumannii, P. aeruginosa, and K. pneumoniae, including polymyxin-resistant MDR clinical isolates. Time-kill studies showed that the combination of polymyxin B (2 mg/L) and mitotane (4 mg/L) provided superior bacterial killing against all strains during the first 6 h of treatment, compared to monotherapies, and prevented regrowth and emergence of polymyxin resistance in the polymyxin-susceptible isolates. Electron microscopy imaging revealed that the combination potentially affected cell division in A. baumannii. The enhanced antimicrobial activity of the combination was confirmed in a mouse burn infection model against a polymyxin-resistant A. baumannii isolate. As mitotane is hydrophobic, it was very likely that the synergistic killing of the combination resulted from that polymyxin B permeabilized the outer membrane of the Gram-negative bacteria and allowed mitotane to enter bacterial cells and exert its antimicrobial effect. These results have important implications for repositioning non-antibiotic drugs for antimicrobial purposes, which may expedite the discovery of novel therapies to combat the rapid emergence of antibiotic resistance.

Highlights

The emergence of Gram-negative bacteria with resistance to multiple classes of antibiotics is causing serious problems for health care centers worldwide (Boucher et al, 2013)
We evaluated the in vitro antimicrobial activity of the combination of polymyxin B and mitotane against highly resistant clinical isolates of Gram-negative bacteria including carbapenemresistant A. baumannii, carbapenem-resistant P. aeruginosa, and New Delhi metallo-β-lactamase (NDM)-producing Klebsiella pneumoniae
In the control group, polymyxin B minimum inhibitory concentrations (MICs) of all isolates at 24 h were not affected as all values remained within two folds of the baseline MICs (European Committee for Antimicrobial Susceptibility Testing (EUCAST) of the European Society of Clinical Microbiology and Infectious Diseases (ESCMID), 2003)

Summary

Introduction

The emergence of Gram-negative bacteria with resistance to multiple classes of antibiotics is causing serious problems for health care centers worldwide (Boucher et al, 2013). Infections caused by multidrug-resistant (MDR) Gram-negative bacteria have higher mortality rates (Harris et al, 2015) and lead to more economic burden than infections caused by susceptible Gram-negative bacteria (Gandra et al, 2014). Among these MDR Gram-negative bacteria, carbapenem-resistant Acinetobacter baumannii has been identified as one of the most difficult-to-treat pathogens and is becoming increasingly problematic for critically ill patients and war-wounded soldiers (Davis et al, 2005; Gupta et al, 2006; Peleg et al, 2008; Centers for Disease Control and Prevention [CDC], 2013). The two main mechanisms of polymyxin resistance identified in Gram-negative bacteria are lipid A modifications and loss of LPS (Moffatt et al, 2010; Arroyo et al, 2011)

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