Polymyxin B in combination with meropenem against carbapenemase-producing Klebsiella pneumoniae: pharmacodynamics and morphological changes

Abstract

Combination therapy provides a useful therapeutic approach to overcome resistance until new antibiotics become available. In this study, the pharmacodynamics, including the morphological effects, of polymyxin B (PMB) and meropenem alone and in combination against KPC-producing Klebsiella pneumoniae clinical isolates was examined. Ten clinical isolates were obtained from patients undergoing treatment for mediastinitis. KPCs were identified and MICs were measured using microbroth dilution. Time–kill studies were conducted over 24 h with PMB (0.5–16 mg/L) and meropenem (20–120 mg/L) alone or in combination against an initial inoculum of ca. 106 CFU/mL. Scanning electron microscopy (SEM) was employed to analyse changes in bacterial morphology after treatment, and the log change method was used to quantify the pharmacodynamic effect. All isolates harboured the blaKPC-2 gene and were resistant to meropenem (MICs ≥8 mg/L). Clinically relevant PMB concentrations (0.5, 1.0 and 2.0 mg/L) in combination with meropenem were synergistic against all isolates except BRKP28 (polymyxin- and meropenem-resistant, both MICs >128 mg/L). All PMB and meropenem concentrations in combination were bactericidal against polymyxin-susceptible isolates with meropenem MICs ≤16 mg/L. SEM revealed extensive morphological changes following treatment with PMB in combination with meropenem compared with the changes observed with each individual agent. Additionally, morphological changes decreased with increasing resistance profiles of the isolate, i.e. increasing meropenem MIC. These antimicrobial effects may not only be a summation of the effects due to each antibiotic but also a result of differential action that likely inhibits protective mechanisms in bacteria.

Synergistic Antimicrobial Activity of Colistin in Combination with Rifampin and Azithromycin against Escherichia coli Producing MCR-1

“…Next, the antibiotics were added to a logarithmic-phase culture at ϳ10 7 CFU/ml, which was obtained by taking a supplement of fresh medium. At the time points of 0, 1,2,4,6,8,12,24,28,32,36, and 48 h after incubation, 100 l of each sample was withdrawn for colony counting. The lower limit of quantification was 2.0 log 10 CFU/ml.…”

“…The increased in vitro bacterial effect of double-or triple-drug combinations of colistin or polymyxin B and various drugs, such as rifampin (6,7), meropenem (8,9), and amikacin (10,11), has been well demonstrated in many studies. Azithromycin is the most commonly prescribed antibiotic, other than for the clinical treatment of serious Gram-negative infections because of poor diffusion across the outer membrane of most Gram-negative bacteria (12).…”

Comparison of methods for the detection of in vitro synergy in multidrug-resistant gram-negative bacteria

“…Multidrug-resistant Gram-negative strains such as A. baumannii, P. aeruginosa, and S. marcescens are commonly studied due to their major role as nosocomial pathogens with frequent development of multidrug resistance [7][8][9][10][11][12][13]. The treatment of infections caused by these microorganisms based on identification of resistance mechanisms and drug combinations is usually more effective than empirical treatment [1,4]. Synergy testing can also correlate to a particular resistance mechanism [8,14].…”

Comparison of methods for the detection of in vitro synergy in multidrug-resistant Gram-negative bacteria

“…Combined antimicrobial therapy is a promising strategy for treating infections caused by MDR pathogens and can further extend antimicrobial lifespan and minimize the evolution of resistance [3,4]. However, despite the importance of in vitro testing, methods that are accessible to clinical microbiology laboratories for testing synergism in a clinically actionable period are not available.…”