Development of a bacteriophage model system to investigate virus inactivation methods used in the treatment of bone allografts

Abstract

Bone allografts are commonly used in a variety of surgical procedures, to reconstruct lost bone stock and to provide mechanical support during the healing process. Due to concerns regarding the possibility of disease transmission from donor to recipient, and of contamination of grafts during retrieval and processing procedures, it is common practice to sterilise bone allografts prior to issue for clinical use. It is vital that the sterilisation processes applied to allografts are validated to demonstrate that they achieve the required level of bioburden reduction, and by extension that validated models are used for these studies. Two common sterilisation protocols applied to bone allografts are gamma irradiation and ethylene oxide gas sterilisation, and there are currently no validated models available for measuring the anti-viral efficacy of ethylene oxide treatment with regard to bone allografts or readily useable models for assessing the anti-viral efficiency of gamma irradiation treatment. We have developed and validated models for both these sterilisation processes, using the bacteriophage varphix174, and utilised the models to measure the antiviral activity of the standard ethylene oxide and gamma irradiation sterilisation processes applied to bone allografts by the National Blood Service. For the irradiation model, we also utilised bacterial spores (Bacillus pumilus). Our results show that ethylene oxide sterilisation (which can only be applied to lyophilised grafts) inactivated > 6.1 log(10) of the model virus, and gamma irradiation (at 25 -40 kGy and applied to frozen allografts) inactivated 3.6 - 4.0 log(10) of the model virus and > 4 log(10) of the bacterial spores. Gamma irradiation at this dosage is therefore not in itself a sterilisation process with respect to viruses.

Bone graft in posterior spine fusion for adolescent idiopathic scoliosis: a meta‐analysis

“…The use of allograft in the thoracolumbar spine in the adolescent population has shown similar fusion results to autograft with decreased morbidity, operation time and blood loss . In addition, several studies have documented the safety of freeze‐dried allograft, however, concerns regarding theoretical disease transmission, limited osteoinductive properties and subsequent questions concerning the rate of successful arthrodesis have dampened some enthusiasm. A variety of other bone graft substitutes are also currently used in orthopaedics including bioactive ceramic granules, beta tricalcium phosphate, coralline hydroxyapatite and osteogenic protein‐1, with variable fusion success rates …”

Disinfection of human musculoskeletal allografts in tissue banking: a systematic review

“…However, there were no assays of tissue integrity, viability, or transplantation outcomes that suggest its safety or efficacy in preserving tissue integrity (Hernigou et al 2000; Saegeman et al 2009; Schubert et al 2012). When samples were treated with ethylene oxide, there was a much narrower range of different conditions tested, but tissue integrity was assessed, which could also provide insight into protocol optimization (Bienek et al 2007; Lomas et al 2001; Moore et al 2004). …”

Local Bacteriophage Delivery for Treatment and Prevention of Bacterial Infections

“…A practical limitation of bacteriophage loaded biomaterials is finding compatible sterilization techniques. The thermosensitive phages cannot undergo high temperature or steam sterilization and the few studies that focused on sterilization of phage loaded biomaterials showed that other common approaches such as EtO gas and γ-irradiation also reduced phage viability significantly (Bienek et al, 2007). Alternatively, the phage incorporation with biomaterials could occur under sterile conditions, but this invites other logistical difficulties and might go against clinical practices of re-sterilizing equipment prior to surgery.…”