Topical release of antibiotics in a polymicrobial biofilm wound model of infection has better biofilm eradication properties that simulated systemic antibiotics

Treatment of diabetic foot infections with systemic antibiotics frequently fails. We aimed to investigate whether sustained release of antibiotics from a calcium sulfate device* at a focal point in a wound model of infection had better efficacy than simulated systemically administered antibiotics.

In order to assess this we were granted ethical approval to collect tissue from subjects on presentation with grade 1B diabetic foot ulcers to harvest the resident microbiota and after a week of treatment a blood sample was taken to assay the concentration of the antibiotic used in treatment. This concentration or where this was unavailable the reported Cmax value was used as the “systemic” condition.

Models were prepared using collagen, extracellular matrix, hyaluronic acid and fibroblasts in a tissue culture insert. A void was created in the surface as components gelled. The combination of bacteria from each subject was inoculated into corresponding sets of models in the void and biofilm developed over 72 hours. Gentamicin and vancomycin loaded calcium sulfate beads were added to the void or the systemic concentration of antibiotics was added to the media for 72 hours.

In total six different sets of polymicrobial biofilms were developed corresponding to each subject. When “systemic” antibiotics were added there were no significant differences in biofilm load. However, bacterial counts were significantly reduced in five of the six biofilms when loaded calcium sulfate was added, biofilm was eradicated in four of these. The biofilm not affected was composed of yeast.

Sustained release of antibiotics at a high concentration close to the biofilm is effective in reducing or eradicating bacteria. Simulated systemic antibiotics in this model do not reach sufficient concentrations to inhibit biofilm.

Trademarked Items (if applicable): *Stimulan Rapid Cure

References (if applicable): Carlson, M. W., Alt-Holland, A., Egles, C., & Garlick, J. A. (2008). Three-dimensional tissue models of normal and diseased skin. Current Protocols in Cell Biology / Editorial Board, Juan S. Bonifacino ... [Et Al.], Chapter 19, Unit 19.9–19.9.17. https://doi.org/10.1002/0471143030.cb1909s41
Dowd, S. E., Wolcott, R. D., Sun, Y., McKeehan, T., Smith, E., & Rhoads, D. (2008). Polymicrobial nature of chronic diabetic foot ulcer biofilm infections determined using bacterial tag encoded FLX amplicon pyrosequencing (bTEFAP). PloS One, 3(10), e3326. https://doi.org/10.1371/journal.pone.0003326
Malone, M., Bjarnsholt, T., McBain, A. J., James, G. A., Stoodley, P., Leaper, D., et al. (2017). The prevalence of biofilms in chronic wounds: a systematic review and meta-analysis of published data. Journal of Wound Care, 26(1), 20–25. https://doi.org/10.12968/jowc.2017.26.1.20
Morley, R., Lopez, F., & Webb, F. (2015). Calcium sulphate as a drug delivery system in a deep diabetic foot infection. Foot (Edinburgh, Scotland), 0(0). https://doi.org/10.1016/j.foot.2015.07.002
Price, B. L., Lovering, A. M., Bowling, F. L., & Dobson, C. B. (2016). Development of a novel collagen wound model to simulate the activity and distribution of antimicrobials in soft tissue during diabetic foot infection. Antimicrobial Agents and Chemotherapy, 60(11), AAC.01064–16–6889. https://doi.org/10.1128/AAC.01064-16
Price, B. L., Morley, R., Bowling, F. L., Lovering, A. M., & Dobson, C. B. (2020). Susceptibility of monomicrobial or polymicrobial biofilms derived from infected diabetic foot ulcers to topical or systemic antibiotics in vitro. PloS One, 15(2), e0228704. https://doi.org/10.1371/journal.pone.0228704