Klinisk institutt 2

Midtveisevaluering - Rune Skjåstad




Antimicrobial effects on bacterial biofilms


Introduction: Staphylococcus epidermidis is part of normal skin flora. Its main virulence factor is the ability to form biofilm on foreign bodies. Bacteria in biofilms are hard to treat due to stagnant growth, production of slimy matrix and cell-cell communication resulting in a heterogeneous bacterial community tolerant to antibiotics and the immune system. Methods for detecting antibiotic effects on biofilms are scarce and not standardized. We wanted to develop a new method and test antibiotic effects on biofilms.


Methods:  A method for testing of time-lapse antibiotic effects based on the viability marker propidium iodide was developed. Biofilms were grown in microtiter-plates, exposed to antibiotics, and results were measured continuously while antibiotics were working.


Results: The new assay detected effects comparable with traditional regrowth methods. Rifampicin showed a rapid dissolving effect on S. epidermidis biofilms while other antibiotic showed minor effects. In combinations most tested antibiotics worked antagonistic on the rifampicin effect.


Discussion: The new method will further be used to test differences in antibiotic effects, interactions using also clinical strains from orthopaedic implants.