Assessment of microbial bioburden methodologies for tissue bank specimens

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Musculoskeletal tissues form part of the skeletal and/or muscular system of the body, vital in providing support and mobility. Musculoskeletal tissue transplants outnumber all other organ and tissue transplants. The bioburden assessment of allograft musculoskeletal tissue must be performed as part of the assessment screening of living and cadaveric donors to minimise the potential risk of transmission of infectious diseases via the allograft to the recipient. There are no guidelines or standard method for determining the bioburden assessment of allograft musculoskeletal tissue and microbiology laboratories may use different types of samples, culture media and methods. Determining the suitability of the allograft tissue sample and the sensitivity of the bioburden testing methods required investigation especially with the advent of nucleic-acid testing (NAT). Subsequently, this investigation highlighted the lack of information regarding microbiology laboratories and the tissue banking industry in Australia. A questionnaire was sent to all Australian tissue banks to determine their current status and the types of allograft samples being collected for bioburden assessment. Another questionnaire was designed for Therapeutic Goods Administration (TGA) licensed clinical microbiology laboratories to establish what bioburden assessment methods were being used for allograft samples. The information obtained from these questionnaires guided the evaluations undertaken in this thesis to compare different allograft samples and methods for bioburden assessment. The current practice of collecting a swab and biopsy sample of allograft musculoskeletal tissue appears optimal for bioburden assessment. Retrospective reviews of isolates recovered from allograft musculoskeletal tissue and from the literature found a wide range of aerobic and anaerobic micro-organisms with fungi infrequently isolated. An evaluation of the Amies gel swab and the ESwab systems was performed to determine if bioburden recovery could be improved at the pre-analytical stage. Both swab systems were found to be suitable sampling devices for bioburden testing of allograft musculoskeletal tissue. The most common bioburden assessment methods, agar and broth culture, were compared with a broad-range NAT method. Swab and biopsy samples were inoculated with known quantities of challenge organisms and the percentage recovery of the challenge organisms was compared. In this study, the NAT method was not more sensitive than the culture-based techniques evaluated with broth culture being the most sensitive. Microbiology laboratories must continue to re-evaluate current methods and investigate new ones to improve sensitivity. Future directions must be cost-effective as the value of maintaining a TGA-licence has become uncertain for some laboratories. Ultimately, tissue banks, clinicians and, most importantly, the allograft recipient must have confidence in the pre-analytical sampling techniques and the testing methods used to determine the bioburden of allograft musculoskeletal tissue prior to transplant.
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