Development of a mixed-species biofilm model and its virulence implications in device related infections.

It is becoming increasingly accepted that to understand and model the bacterial colonization and infection of abiotic surfaces requires the use of a biofilm model. There are many bacterial colonizations by at least two primary species, however this is difficult to model in vitro. This study reports the development of a simple mixed-species biofilm model using strains of two clinically significant bacteria: Staphylococcus aureus and Pseudomonas aeruginosa grown on nanoporous polycarbonate membranes on nutrient agar support. Scanning electron microscopy revealed the complex biofilm characteristics of two bacteria blending in extensive extracellular matrices. Using a prototype wound dressing which detects cytolytic virulence factors, the virulence secretion of 30 single and 40 mixed-species biofilms was tested. P. aeruginosa was seen to out-compete S. aureus, resulting in a biofilm with P. aeruginosa dominating. In situ growth of mixed-species biofilm under prototype dressings showed a real-time correlation between the viable biofilm population and their associated virulence factors, as seen by dressing fluorescent assay. This paper aims to provide a protocol for scientists working in the field of device related infection to create mixed-species biofilms and demonstrate that such biofilms are persistently more virulent in real infections. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 107B: 129-137, 2019.

Antimicrobial Activity of a Novel Vascular Access Film Dressing Containing Chlorhexidine Gluconate.

BACKGROUND: Covering insertion sites with chlorhexidine impregnated dressings has been proven to be clinically effective in reducing catheter related blood stream infections (CR-BSI). Two chlorhexidine gluconate (CHG)-impregnated dressings are commercially available, a polyurethane foam disk and a film dressing containing a chlorhexidine gluconate-impregnated gel pad. While both have demonstrated efficacy in clinical settings, the major drawback of high cost and impaired IV insertion site visibility limits their usage. A new, simple film dressing containing CHG within its adhesive layer is now available. The objective of this study was to test the in vitro antimicrobial efficacy of the new dressing in comparison to the CHG-impregnated gel dressing. METHODS: Quantitative aliquots of suspensions (concentration of 1.0x106 to 5.0x106 cfu/sample) of clinically relevant challenge organisms (Staphylococcus species, gram-negative bacilli, Candida albicans) were incubated in contact with the new CHG-containing film dressing, a placebo version of the same (negative control) and the commercially available CHG-impregnated gel dressing (positive control). Serial dilutions of the surviving organisms were quantified using the pour plate after 1, 3, 5, and 7 days of incubation in order to calculate an antimicrobial log10 reduction for each organism/dressing combination at each point in time. RESULTS: The new CHG-containing film dressing delivered greater than 5.0 log10 reduction throughout the 7 days on all aerobic gram-negative bacilli and Staphylococcus species tested. As of day 1 the CHG-containing film dressing provided greater than 5.0 log10 reduction on Candida albicans. There were no statistically significant differences in the log10 reduction between the two dressings tested. CONCLUSION: The new CHG-containing film dressing was found to be as effective as the chlorhexidine gluconate-impregnated gel dressing on clinically relevant microbes.

Antimicrobial activity of a novel adhesive containing chlorhexidine gluconate (CHG) against the resident microflora in human volunteers.

OBJECTIVES: To evaluate the antimicrobial activity of a new, transparent composite film dressing, whose adhesive contains chlorhexidine gluconate (CHG), against the native microflora present on human skin. METHODS: CHG-containing adhesive film dressings and non-antimicrobial control film dressings were applied to the skin on the backs of healthy human volunteers without antiseptic preparation. Dressings were removed 1, 4 or 7 days after application. The bacterial populations underneath were measured by quantitative cultures (cylinder-scrub technique) and compared with one another as a function of time. RESULTS: The mean baseline microflora recovery was 3.24 log10 cfu/cm(2). The mean log reductions from baseline measured from underneath the CHG-containing dressings were 0.87, 0.78 and 1.30 log10 cfu/cm(2) on days 1, 4 and 7, respectively, compared with log reductions of 0.67, -0.87 and -1.29 log10 cfu/cm(2) from underneath the control film dressings. There was no significant difference between the log reductions of the two treatments on day 1, but on days 4 and 7 the log reduction associated with the CHG adhesive was significantly higher than that associated with the control adhesive. CONCLUSIONS: The adhesive containing CHG was associated with a sustained antimicrobial effect that was not present in the control. Incorporating the antimicrobial into the adhesive layer confers upon it bactericidal properties in marked contrast to the non-antimicrobial adhesive, which contributed to bacterial proliferation when the wear time was ≥4 days.