Biofilm-forming skin microflora bacteria are resistant to the bactericidal action of disinfectants used during blood donation


  • MT is a recipient of a Graduate Fellowship awarded by Canadian Blood Services and Health Canada. Funding for this research was provided by Canadian Blood Services and Health Canada although the views expressed herein do not necessarily represent those of the Canadian federal government.



A one-step skin disinfection method containing 2% chlorhexidine-gluconate (CHG) and 70% isopropyl alcohol (IPA) is currently used by blood suppliers worldwide. Reports of bacterially contaminated platelet concentrates (PCs) indicate that skin disinfection is not fully effective. Approximately 20% of skin microflora exist as surface-attached aggregates (biofilms), known for displaying increased resistance to disinfectants. This study was aimed at determining whether skin microflora biofilm-positive Staphylococcus epidermidis and Staphylococcus capitis are resistant to CHG and/or IPA.

Study Design and Methods

Free-floating cells and mono or dual (1 : 1 ratio) biofilms of S. epidermidis and S. capitis were exposed to CHG, IPA, or CHG/IPA for 30 seconds, simulating skin disinfection practices. Residual viable cells were quantified by colony counting. Morphology of disinfectant-treated S. epidermidis biofilms was examined by scanning electron microscopy. Treated S. epidermidis and S. capitis biofilms were inoculated into PCs and bacterial concentrations were determined on Days 0 and 5 of storage.


Treatment of staphylococcal biofilm cells with all disinfectants caused cell damage and significant reduction in viability, with CHG/IPA being the most effective. However, biofilms were significantly more resistant to treatment than free-floating cells. Disinfectant-treated S. epidermidis proliferated better in PCs than S. capitis, especially when grown as monospecies biofilms.


Although CHG/IPA is effective in reducing the viability of S. epidermidis and S. capitis biofilms, these organisms are not completely eliminated. Furthermore, disinfectant-treated staphylococcal biofilms multiply well in PCs. These results demonstrate that the biofilm-forming capability of the skin microflora reduces the bactericidal efficiency of blood donor skin disinfectants.