Utility of a commercially available transwell system for assessment of MSC-mediated mitigation of biofilms

Mesenchymal stromal cells (MSC) reduce and prevent biofilm infections in a paracrine fashion by secretion of antimicrobial proteins. However, studies to-date have used conditioned cell culture medium alone rather than allowing real-time MSC-biofilm interaction. A co-culture method to evaluate MSC efficacy in reducing established biofilms is needed to facilitate MSC-bacterial interactions while enabling biofilm separation for imaging and quantification after co-culture. We describe the development of a novel in vitro method to co-culture established S. aureus and E. coli biofilms with equine bone marrow-derived MSC ± amikacin sulfate using a commercially available transwell plate system. The system was used to co-culture MSC from 6 horses with mature biofilms and perform analysis of biomass by crystal violet assay, bioburden by colony forming unit analysis and biofilm size by quantitative photographic analysis using Image J. Our method allowed downstream quantification of biofilm biomass, live bacterial counts, and photographic analysis of biofilm size and may be used for high-throughput evaluation of MSC as a treatment for biofilm infections.