<p>A novel mechanism of action of ketoconazole: inhibition of the <em>NorA</em> efflux pump system and biofilm formation in multidrug-resistant <em>Staphylococcus aureus</em></p>

Abstract

Background: The rapid emergence of antimicrobial resistance among Gram-positive organisms, especially staphylococci, has become a serious clinical challenge. Efflux machinery and biofilm formation are considered two of the main causes of antimicrobial resistance and therapy failure. Aim: Our study aims to evaluate the antibiofilm and efflux pump inhibitory activity of the antifungal ketoconazole against multidrug-resistant (MDR) Staphylococcus aureus . Methods: Ketoconazole was tested for its effect on the following: minimum inhibitory concentrations (MICs) of ciprofloxacin, norfloxacin, levofloxacin, and ethidium bromide (EtBr) by the broth microdilution method, the efflux of EtBr by NorA -positive MDR S. aureus , and the relative expression of NorA, NorB , and NorC efflux pump genes. Docking studies of ketoconazole were performed using 1PW4 (glycerol-3-phosphate transporter from Escherichia coli which was the representative structure from the major facilitator superfamily). Results: Ketoconazole significantly decreased the MICs of levofloxacin, ciprofloxacin, norfloxacin, and EtBr (a substrate for efflux pump) by 8 to 1024-fold ( P <0.01) and decreased the efflux of EtBr. Furthermore, a time-kill assay revealed that combinations of levofloxacin with ketoconazole or carbonyl cyanide m-chlorophenylhydrazone showed no growth for the tested strains after 24 h in comparison to the effect of levofloxacin alone. Docking studies and the ability of ketoconazole to diminish the relative expression of NorA gene in comparison to control (untreated strains) confirmed its action as an efflux pump inhibitor. Conclusion: The findings showed that the antifungal ketoconazole has no antibacterial activity but can potentiate the activity of the fluroquinolones against MDR S. aureus via inhibiting efflux pump and biofilm formation in vitro.

<p>Prevalence and Some Possible Mechanisms of Colistin Resistance Among Multidrug-Resistant and Extensively Drug-Resistant <em>Pseudomonas aeruginosa</em></p>

“…Recently, multidrug-resistant pathogenic bacterial strains appear where most of the available antibiotics are not effective against them. 6,[32][33][34][35][36] The polymyxins considered the last resort for treatment of multi-drug resistant bacterial infections, so studying the emergence of colistinresistant was a must. Polymyxins showed their activity through their electrostatic interaction between them and the negatively charged moieties on the lipid A of Gramnegative bacteria resulting in the destabilization of the outer membrane and the leakage of the cytoplasmic content and lysis.…”

<p>Methicillin-Resistant <em>Staphylococcus aureus</em> (MRSA): One Health Perspective Approach to the Bacterium Epidemiology, Virulence Factors, Antibiotic-Resistance, and Zoonotic Impact</p>

“…Infected animals with MRSA must be isolated and treated and infected wounds with MRSA should be disinfected and covered. [111][112][113][114]…”

Synthesis and Evaluation of 2‐Aminothiophene Derivatives as Staphylococcus aureus Efflux Pump Inhibitors

“…Efflux pumps are integral transmembrane proteins capable of extruding antimicrobials agents and dyes, among other toxic compounds out of the bacterial cell . The efflux proteins are subdivided into five main families …”