High hydrostatic pressure as a means to eliminate bacteria from bone tissue

Bone tumors, severe fractures, infections, or revision arthroplasties require surgical intervention of the musculoskeletal system, that often results in defects exceeding the self-healing capabilities of bone. Allografts, mostly taken from deceased donors, are crucial in the reconstruction of such defect areas. However, allogeneic bone grafts need preoperative processing to reduce the immunogenic burden and to eliminate a potential microbial load.

This study investigates the microbiological aspects of high hydrostatic pressure (HHP) treatment as a processing method for bone tissue. In order to reduce contaminations while preserving its osteoinductive features and structural integrity, HHP treatment parameters were systematically optimized.

Two model organisms, Escherichia coli and Micrococcus luteus, underwent HHP treatment of up to 600 MPa, with variations in pressure level, treatment duration, temperature, and pressurization medium. Colony forming units were determined for the calculation of logarithmic reduction factors. Bovine cancellous bone blocks, artificially contaminated with E. coli and M. luteus, were subjected to a tailored HHP protocol to assess the protective effect of the surrounding tissue.

Results indicate a correlation between bacterial load reduction and applied pressure level. Lowering treatment temperature from 20 °C to 10 °C significantly increased treatment efficiency. Furthermore, the pressurization medium had a significant influence, with 0.9% sodium chloride solution supplemented with low concentrations of surfactants like SDS and EDTA proving most effective in inactivation. Despite being less effective than in bacterial suspensions, a reduction in bioburden was also observed in the artificially contaminated bone blocks.

This study demonstrates the efficiency of HHP treatment in inactivating bacteria in suspension and when associated with bone tissue. Further investigation of HHP treatment protocols that balance microbiological safety, biocompatibility and tissue integrity and analysis of underlying mechanisms may enable improvement of clinical outcome after allogeneic bone grafting.