Objective-To determine whether or not there are any significant differences in the effects of wound dressings on bacterial bioburden.Method-A selection of non-occlusive, non-adhesive dressings was tested for their effect on bacterial bioburden. The dressings selected included two dressings with antimicrobial properties (one containing silver and one containing PHMB), a cotton-based dressing enclosed in a perforated sleeve of poly(ethylene terephthalate), a carboxymethyl cellulose-based dressing, a fibre-free alginate dressing, and a 12-ply 100% cotton gauze. Using the colony-drip flow reactor (DFR) model, a meticillin-resistant Staphylococcus aureus (MRSA) or Pseudomonas aeruginosa biofilm was grown underneath a dressing sample. Biofilm growth was examined via plate counts, fluorescent microscopy and scanning electron microscopy.Results-The dressings containing antimicrobial agents had the greatest effect on bacterial load. In the MRSA experiments, both antimicrobial dressings produced lower bacteria counts than the other dressings (p≤0.001), while in the P. aeruginosa experiments, only the silver-containing sample had fewer bacteria (p≤0.0001). However, neither antimicrobial dressing was able to completely eradicate the bacteria when testing with either microorganism. Conclusion-The results presented herein illustrate that bacteria can grow unchallenged within the dressing environment and that an antimicrobial dressing can limit this bacterial growth. Keywordsantimicrobial dressings; biofilms; plate counts; fluorescent microscopy; scanning electron microscopy Wounds are an ideal environment for bacterial colonisation and biofilm formation. The wound bed provides both a surface on which to grow and an ample supply of nutrients. Recent studies have shown that bacteria inoculated into wounds form biofilms. 1,2 Another study found that as many as 60% of chronic wound specimens contained a biofilm. 3 Current research indicates that biofilms are present in chronic wounds. [3][4][5][6] Furthermore, recent studies suggest that biofilms should be targeted when developing and testing therapies for these wounds. [7][8][9][10][11] A literature review of culture data from 62 published studies dating from 1969 to 1997 revealed that the predominant wound isolate in both chronic and acute wounds was Staphylococcus aureus (reported in 63% of the studies), followed by coliforms (45%), Bacteroides spp. (39%), Peptostreptococcus spp. (36%), Pseudomonas aeruginosa (29%), Enterococcus spp. (26%) and Streptococcus pyogenes (13%).

Aims:  To develop an in vitro model (Colony/drip‐flow reactor – C/DFR) for the growth and analysis of methicillin‐resistant Staphylococcus aureus (MRSA) biofilms. Methods and Results:  Using the C/DFR model, biofilms were grown on the top of polycarbonate filter membranes inoculated with a clinical isolate of MRSA, placed on absorbent pads in the DFR and harvested after 72 h. The biofilms varied from 256 to 308 μm in thickness with a repeatability standard deviation of 0·22. Testing of antimicrobial agents was also performed where C/DFR biofilms were grown in parallel with conventional colony biofilms. A saline solution (control), 1% silver sulfadiazine solution, and 0·25% Dakin’s solution were used to treat the biofilms for 15 min. Microscopic evaluation of biofilm morphology and thickness was conducted. The Dakins solution in both models produced statistically significantly higher log reductions than silver sulfadiazine treatment. Conclusions:  The C/DFR biofilms were thick and repeatable and exhibited higher resistance to Dakins solution than the treated colony biofilms. Significance and Impact of the Study:  The C/DFR can be used as a tool for examining complex biofilm physiology as well as for performing comparative experiments that test wound care products and novel antimicrobials.