Assessment Of Bacterial Contamination Of Retrieved Musculoskeletal Allograft Tissue

Chowdhury, Nazim (2006). Assessment Of Bacterial Contamination Of Retrieved Musculoskeletal Allograft Tissue. MPhil thesis The Open University.



Tissues retrieved from cadavers are increasingly banked and used for transplantation but few bacteriological standards for the safety of the tissues have been established. This study sets out i) to investigate the sources of contamination of the cadaveric tissues, ii) to determine the optimal method for sampling of tissue for bacteria and iii) to assess the use of ethanol as a general purpose sterilant for contaminated tissues.

The sources of contamination were investigated by attempting to match the DNA fingerprints of bacteria recovered from tissue post retrieval with isolates recovered from donor’s skin, mortuary air and retrieval staff clothes. Isolates were identified to species level and DNA fingerprints were determined by random amplified polymorphic DNA (RAPD) profiling.

Contaminated tissues were found in 18 of 20 retrievals. Staphylococcal species, particularly coagulase negative species were among the most prevalent bacteria recovered from tissues. Staphylococcus epidermidis was present in 70% of the 20 retrievals, followed by Micrococcus spp. (50%), and S. capitis (45%). Other organisms were relatively uncommon, although Escherichia coli was recovered from 5 donors.

RAPD profiles showed that 16/35 (46%) of tissue and donor isolates of the same species from each retrieval were indistinguishable from each other and the corresponding rate of RAPD profiles of isolates from staff and tissue was 31%. There was no significant difference between the number of matches of isolates from donor and staff, and retrieved tissue isolates (P>0.05). Both staff and donor were the most common sources for contamination of cadaveric tissue during retrieval and to a lesser degree, the circulating air in mortuaries (20%).

Experiments showed that culturing of small aliquots of wash solutions was insensitive for the detection of bacteria. Culture of a filtered wash detected both high and low levels of contamination but was not reproducible. Swabbing of the tissue surface with a moist swab also gave variable results but did allow the growth of various bacteria following enrichment in liquid media.

Exposure to 70% ethanol for 60 min proved to be an effective sterilant of contaminated tendons, but it was necessary to remove as much muscle tissue as possible from the tissue before the treatment. Prewashing of tissue in a mild detergent improved the effectiveness of alcohol treatment.

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