minocycline and phenylalanine-arginine-beta-naphthylamide

Acinetobacter baumannii are non-fermentative, Gram-negative bacilli that cause a large number of nosocomial infections worldwide. They are characterized by frequent multiresistance due to multiple mechanisms. As a consequence, infections caused by strains exhibiting resistance to carbapenems and, sometimes, polymyxins, are regularly observed. Sulbactam, colistin and combinations of different antimicrobials have been reported as new therapeutic approaches for infections caused by resistant A baumannii strains. This review focuses on current and potential new drugs, such as rifampin, tigecycline, antimicrobial peptides, efflux pump resistant and inhibitor drugs, and enzyme inhibitors.

Topics: Acinetobacter baumannii; Acinetobacter Infections; Anti-Bacterial Agents; Antimicrobial Cationic Peptides; Clinical Trials as Topic; Dipeptides; Drug Resistance, Multiple, Bacterial; Enzyme Inhibitors; Humans; Minocycline; Molecular Structure; Rifampin; Tigecycline

Multidrug efflux protein complexes such as AcrAB-TolC from Escherichia coli are paramount in multidrug resistance in Gram-negative bacteria and are also implicated in other processes such as virulence and biofilm formation. Hence efflux pump inhibition, as a means to reverse antimicrobial resistance in clinically relevant pathogens, has gained increased momentum over the past two decades. Significant advances in the structural and functional analysis of AcrB have informed the selection of efflux pump inhibitors (EPIs). However, an accurate method to determine the kinetics of efflux pump inhibition was lacking. In this study we standardised and optimised surface plasmon resonance (SPR) to probe the binding kinetics of substrates and inhibitors to AcrB. The SPR method was also combined with a fluorescence drug binding method by which affinity of two fluorescent AcrB substrates were determined using the same conditions and controls as for SPR. Comparison of the results from the fluorescent assay to those of the SPR assay showed excellent correlation and provided validation for the methods and conditions used for SPR. The kinetic parameters of substrate (doxorubicin, novobiocin and minocycline) binding to AcrB were subsequently determined. Lastly, the kinetics of inhibition of AcrB were probed for two established inhibitors (phenylalanine arginyl β-naphthylamide and 1-1-naphthylmethyl-piperazine) and three novel EPIs: 4-isobutoxy-2-naphthamide (A2), 4-isopentyloxy-2-naphthamide (A3) and 4-benzyloxy-2-naphthamide (A9) have also been probed. The kinetic data obtained could be correlated with inhibitor efficacy and mechanism of action. This study is the first step in the quantitative analysis of the kinetics of inhibition of the clinically important RND-class of multidrug efflux pumps and will allow the design of improved and more potent inhibitors of drug efflux pumps. This article is part of a Special Issue entitled: Beyond the Structure-Function Horizon of Membrane Proteins edited by Ute Hellmich, Rupak Doshi and Benjamin McIlwain.

Topics: Anti-Bacterial Agents; Antibiotics, Antineoplastic; Dipeptides; Doxorubicin; Drug Resistance, Multiple, Bacterial; Escherichia coli; Escherichia coli Proteins; Kinetics; Minocycline; Molecular Structure; Multidrug Resistance-Associated Proteins; Naphthalenes; Novobiocin; Piperazines; Protein Binding; Surface Plasmon Resonance

Gene inactivation and complementation experiments showed that the tripartite AheABC efflux pump of Aeromonas hydrophila extruded at least 13 substrates, including nine antibiotics. The use of phenylalanine-arginine-beta-naphthylamide (PAbetaN) revealed an additional system(s) contributing to intrinsic resistance. This is the first analysis of the role of multidrug efflux systems in Aeromonas spp.

Topics: Aeromonas hydrophila; Anti-Bacterial Agents; Bacterial Proteins; Biological Transport, Active; Dipeptides; Drug Resistance, Multiple, Bacterial; Humans; Microbial Sensitivity Tests; Molecular Sequence Data; Sequence Analysis, DNA; Substrate Specificity

Tigecycline has shown in vitro activity against Acinetobacter baumannii. Yet, published clinical experience with tigecycline use outside clinical trials is lacking. We describe, for the first time, bloodstream infection caused by tigecycline-non-susceptible A. baumannii occurring in patients receiving tigecycline for other indications. The possible mechanisms of resistance and pharmacokinetic limitations of the drug are addressed.. The clinical records of involved patients were systematically reviewed. Tigecycline susceptibility testing was initially performed using the Etest method and confirmed by agar dilution. Involved isolates underwent PFGE and exposure to phenyl-arginine-beta-naphthylamide (PAbetaN), an efflux pump inhibitor.. Two patients developed A. baumannii bloodstream infection while receiving tigecycline. Tigecycline was administered for other indications for 9 and 16 days, respectively, before the onset of A. baumannii infection. Patient 1 died of overwhelming A. baumannii infection and Patient 2 recovered after a change in antibiotic therapy. The MICs of tigecycline were 4 and 16 mg/L, respectively. Both isolates had a multidrug-resistant phenotype and were genotypically unrelated. After exposure to PAbetaN, the MICs reduced to 1 and 4 mg/L, respectively.. To our knowledge, this is the first clinical description of bloodstream infection caused by tigecycline-non-susceptible A. baumannii. Such resistance appears to be at least partly attributable to an efflux pump mechanism. Given the reported low serum tigecycline levels, we urge caution when using this drug for treatment of A. baumannii bloodstream infection.

Topics: Acinetobacter baumannii; Aged; Anti-Bacterial Agents; Bacteremia; Dipeptides; Drug Resistance, Bacterial; Electrophoresis, Gel, Pulsed-Field; Female; Humans; Male; Microbial Sensitivity Tests; Middle Aged; Minocycline; Tigecycline