Abstract
Polymyxins are used as a last-resort class of antibiotics against multidrug-resistant (MDR) Gram-negative Pseudomonas aeruginosa. As polymyxin monotherapy is associated with potential development of resistance, combination therapy is highly recommended. This study investigated the mechanism underlying the synergistic killing of polymyxin B and enrofloxacin against extensive drug-resistant (XDR) P. aeruginosa. An XDR isolate P. aeruginosa 12196 was treated with clinically relevant concentrations of polymyxin B (2 mg/L) and enrofloxacin (1 mg/L) alone or in combination. Metabolome profiles were investigated from bacterial samples collected at 1-and 4-h posttreatment using liquid chromatography with tandem mass spectrometry (LC-MS/MS), and data were analyzed using univariate and multivariate statistics. Significantly perturbed metabolites (q < 0.05, fold change ≥ 2) were subjected to pathway analysis. The synergistic killing by polymyxin B–enrofloxacin combination was initially driven by polymyxin B as indicated by the perturbation of lipid metabolites at 1 h in particular. The killing was subsequently driven by enrofloxacin via the inhibition of DNA replication, resulting in the accumulation of nucleotides at 4 h. Furthermore, the combination uniquely altered levels of metabolites in energy metabolism and cell envelope biogenesis. Most importantly, the combination significantly minimized polymyxin resistance via the inhibition of lipid A modification pathway, which was most evident at 4 h. This is the first study to elucidate the synergistic mechanism of polymyxin B–enrofloxacin combination against XDR P. aeruginosa. The metabolomics approach taken in this study highlights its power to elucidate the mechanism of synergistic killing by antibiotic combinations at the systems level.
Highlights
Extensive drug-resistant (XDR) Pseudomonas aeruginosa is a major burden to the global health-care system and has been highlighted by the World Health Organization as a priority pathogen with “Serious” threat to human health (Mcphee et al, 2006; Gales et al, 2011; World Health Organization, 2014)
Metabolomics Profiles of Pseudomonas aeruginosa Treated With Polymyxin B, Enrofloxacin, and the Combination
The intra-experimental variability was assessed based on the median relative standard deviations (RSDs) of the samples, which ranged from 15% to 24% (Figure S1) and were well within the acceptable limits for metabolomics studies (Kirwan et al, 2014)
Summary
Extensive drug-resistant (XDR) Pseudomonas aeruginosa is a major burden to the global health-care system and has been highlighted by the World Health Organization as a priority pathogen with “Serious” threat to human health (Mcphee et al, 2006; Gales et al, 2011; World Health Organization, 2014). Polymyxins remain effective against XDR P. aeruginosa, recent pharmacokinetic/pharmacodynamic (PK/PD) studies suggest that polymyxin monotherapy is potentially associated with increased emergence of resistance (Tam et al, 2005; Cheah et al, 2015; Cheah et al, 2016b). Reports of infections caused by XDR P. aeruginosa, including polymyxin-resistant XDR isolates, are on the rise (Hsueh et al, 1998; Adams et al, 2009; Gales et al, 2012; Goli et al, 2016). In a recent in vitro PK/ PD study, we demonstrated that polymyxin B in combination with enrofloxacin is highly effective against XDR P. aeruginosa, which is resistant to both, and significantly minimizes the emergence of polymyxin resistance (Lin et al, 2018). The underlying mechanism of the synergistic killing by this novel drug combination remains unknown
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