Antibacterial activity of human defensins againstStaphylococcus aureusandEscherichia coli

Abstract

BackgroundThe global problem of antibiotic resistance requires the search for and development of new methods of treatment. One of the promising strategies is the use of low doses of antimicrobial peptides, in particular, human defensins HNP-1, hBD-1, and hBD-3, in combination with antibacterial drugs already used in clinical practice. This approach may be used to increase the effectiveness of conventional antibiotics. However, this requires thorough study of the effectiveness of defensins in combination with antibiotics against a large number of bacterial strains with known phenotypes of antibiotic resistance. The aim of this work was to study the antibacterial effect of HNP-1, hBD-1 and hBD-3 in combination with rifampicin or amikacin against clinical isolates ofStaphylococcus aureus(n= 27) andEscherichia coli(n= 24) collected from hospitalized patients.MethodsThe standard checkerboard assay was used to determine minimum inhibitory concentrations (MICs) of antimicrobials. The combined microbicidal effects of two substances (defensin + conventional antibiotic) were assessed by the fractional inhibitory concentration index (FICI).ResultsThe highest anti-staphylococcal activity (including methicillin-resistant strains) among defensins was demonstrated by hBD-3 that had MIC of 1 (0.5–4) mg/L (hereinafter, MIC values are presented as median and interquartile range). The MIC of HNP-1 againstS. aureuswas 4 (2–8) mg/L; the MIC of hBD-1 was 8 (4–8) mg/L. AgainstE. coli, the most effective was also found to be hBD-3 that had MIC of 4 (4–8) mg/L; the MIC of HNP-1 was 12 (4–32) mg/L. The combinations of HNP-1 + rifampicin and hBD-3 + rifampicin demonstrated synergistic effects againstS.aureus. AgainstE. coli, combinations of HNP-1 + amikacin and hBD-3 + amikacin also showed synergy of action.