In-vitro activity of polyhexanide alone and in combination with antibiotics against Staphylococcus aureus

The resistance of Staphylococcus aureus is increasing, not only to antibiotics but also to antiseptics.

To investigate the activity of the antiseptic polyhexanide and several antibiotics against clinical isolates of meticillin-susceptible and meticillin-resistant Staphylococcus aureus (MSSA and MRSA, respectively). Polyhexanide was tested alone and in combination with oxacillin, penicillin G, ampicillin, cefazolin, cefuroxime, imipenem, gentamicin, erythromycin, doxycycline, levoflocaxin, linezolid and vancomycin.

Fifty MSSA and 50 MRSA strains, including one vancomycin-intermediate (VISA) strain, were tested. All strains were typed by pulsed-field gel electrophoresis (PFGE) to exclude testing of clonal isolates. Minimum inhibitory concentrations (MICs) and minimum bactericidal concentrations (MBCs) were determined using the serial broth microdilution technique according to DIN 58940. Combinations of polyhexanide and different antibiotics were investigated using the checkerboard technique.

Polyhexanide MICs and MBCs in the range of 0.5-2mg/L were found for both MSSA and MRSA, and the VISA strain had MIC and MBC values of 2mg/L. All isolates were regarded as susceptible to polyhexanide, and no antagonism was observed between polyhexanide and the tested antibiotics. Synergism between polyhexanide and some bacteriostatic antibiotics (erythromycin, doxycycline and linezolid) was found for some strains.

Polyhexanide appears to be suitable for the topical treatment of S. aureus alone and in combination with antibiotics.