High in vitro antimicrobial activity of synthetic antimicrobial peptidomimetics against staphylococcal biofilms

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ObjectivesThe aim of the study was to investigate the antimicrobial effect of different antibiotics and synthetic antimicrobial peptidomimetics (SAMPs) on staphylococcal biofilms.MethodsBiofilms of six staphylococcal strains (two Staphylococcus haemolyticus, two Staphylococcus epidermidis and two Staphylococcus aureus isolates) were grown for 24 h in microtitre plates. They were washed and treated for 24 h with different concentrations of linezolid, tetracycline, rifampicin and vancomycin and four different SAMPs. After treatment, the redox indicator Alamar Blue was used to quantify metabolic activity of bacteria in biofilms, and confocal laser scanning microscopy with LIVE/DEAD staining was used to further elucidate any effects.ResultsAt MIC levels, rifampicin and tetracycline showed a marked reduction of metabolic activity in the S. epidermidis and S. haemolyticus biofilm. Linezolid had a moderate effect and vancomycin had a poor effect. MIC ×10 and MIC ×100 improved the antimicrobial activity of all antibiotics, especially vancomycin. However, metabolic activity was not completely suppressed in strong biofilm-producing strains. At MIC ×10, the three most effective SAMPs (Ltx5, Ltx9 and Ltx10) were able to completely eliminate metabolic activity in the S. epidermidis and S. haemolyticus biofilms, which was also confirmed by complete cell death using confocal laser scanning microscopy investigations. Although none of the Ltx SAMPs could fully suppress metabolic activity in the S. aureus biofilm, their effect was superior to all tested antibiotics.ConclusionsSAMPs had superior antimicrobial activity in staphylococcal biofilms compared with conventional antibiotics and are potential new therapeutic agents for biofilm-associated infections.

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