Synergistic antibacterial effect of co-administering adipose-derived mesenchymal stromal cells and Ophiophagus hannah L-amino acid oxidase in a mouse model of methicillin-resistant Staphylococcus aureus-infected wounds

Mesenchymal stromal cells (MSCs) and Ophiophagus hannah L-amino acid oxidase (Oh-LAAO) have been reported to exhibit antimicrobial activity against methicillin-resistant Staphylococcus aureus (MRSA). Published data have indicated that synergistic antibacterial effects could be achieved by co-administration of two or more antimicrobial agents. However, this hypothesis has not been proven in a cell- and protein-based combination. In this study, we investigate if co-administration of adipose-derived MSCs and Oh-LAAO into a mouse model of MRSA-infected wounds would be able to result in a synergistic antibacterial effect.

We demonstrated that co-administration of MSCs and Oh-LAAO into a mouse model of MRSA-infected wounds exhibited a synergistic antibacterial effect which significantly reduced the bacterial count and accelerated the wound healing process.

MSCs and Oh-LAAO were isolated and characterized by standard methodologies. The effects of the experimental therapies were evaluated in C57/BL6 mice. The animal study groups consisted of full-thickness uninfected and MRSA-infected wound models which received Oh-LAAO, MSCs, or both. Oh-LAAO was administered directly on the wound while MSCs were delivered via intradermal injections. The animals were housed individually with wound measurements taken on days 0, 3, and 7. Histological analyses and bacterial enumeration were performed on wound biopsies to determine the efficacy of each treatment.

Immunophenotyping and differentiation assays conducted on isolated MSCs indicated expression of standard cell surface markers and plasticity which corresponds to published data. Characterization of Oh-LAAO by proteomics, enzymatic, and antibacterial assays confirmed the identity, purity, and functionality of the enzyme prior to use in our subsequent studies. Individual treatments with MSCs and Oh-LAAO in the infected model resulted in reduction of MRSA load by one order of magnitude to the approximate range of 6 log10 colony-forming units (CFU) compared to untreated controls (7.3 log10 CFU). Similar wound healing and improvements in histological parameters were observed between the two groups. Co-administration of MSCs and Oh-LAAO reduced bacterial burden by approximately two orders of magnitude to 5.1 log10 CFU. Wound closure measurements and histology analysis of biopsies obtained from the combinational therapy group indicated significant enhancement in the wound healing process compared to all other groups. Conclusions: We demonstrated that co-administration of MSCs and Oh-LAAO into a mouse model of MRSA-infected wounds exhibited a synergistic antibacterial effect which significantly reduced the bacterial count and accelerated the wound healing process.