Equine Mesenchymal Stem Cells Possess Antimicrobial Properties

Introduction: Increasing incidence of infections with multi-drug resistant (MDR) organisms and rapid development of antibiotic resistance necessitate the development of novel therapeutics. Stem cell-based therapies have antimicrobial activity and thus are an attractive alternative. Our objectives were to assess antimicrobial activity of eqMSC in vitro against gram-positive and negative bacteria and determine if eqMSC produced antimicrobial peptides. Our hypotheses were that eqMSC exerted a direct antimicrobial effect in vitro against gram-positive and negative bacteria and would produce antimicrobial peptides.

Materials and Methods: Conditioned medium was collected from bone marrow-derived eqMSC and assessed for antibacterial activity in vitro. Log phase bacteria were added to eqMSC conditioned medium and incubated and quantitative cultures were performed. Bacteria utilized included laboratory strains of methicillin-resistant Staphylococcus aureus (MRSA) and Escherichia coli. Results were compared utilizing an ANOVA with Tukey posttest and significance set at p < 0.05. Immunofluorescent antibodies were utilized to determine if eqMSC produced antimicrobial peptides (AMP) in the cathelicidin family.

Results: Equine MSC conditioned medium demonstrated marked inhibition of bacterial growth of S. aureus and E.coli. Equine MSC produced cathelicidin AMPs.

Discussion/Conclusion: This study did not address potential indirect immunomodulatory effect of eqMSCs or effectiveness in vivo. The antimicrobial action of eqMSC may be effective as a therapy where conventional pharmaceutical therapies are ineffective at clearing infection, such as infectious arthritis, orthopaedic implant or musculoskeletal infection with MDR bacteria.

Acknowledgement: There was no proprietary interest or funding provided for this project.