Microbiological examination of donated human cardiac tissue in heart valve banking
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Objective: Microbiological examination of donated human cardiac tissue is a necessary procedure for Heart Valve Banks to determine the biological safety of preserved allografts. Test protocols must be validated to prevent false-negative outcomes that pose a risk of infection to recipients of the tissue. The Heart Valve Bank in Rotterdam evaluated a validated, alternative entry test for donated tissues to compare the performance of its standard microbiological examinations. Methods: Samples of explanted heart transport medium from 275 donors were examined for the presence of microorganisms using blood culture flasks (standard test) and fluid thioglycolate medium (alternative test). Results were compared with the outcome of microbiological assessment of subvalvular myocardial fragments and the cryoprotective medium that were collected before and after treatment of the grafts with antibiotics, respectively. Results: Microorganisms, mainly skin flora, were detected in transport medium of 177 hearts (64%). The alternative validated culture method detected a growth in 80 transport medium samples that was not identified by the standard method. Microorganisms were only identified in the cultivated cardiac tissue fragments from 56 donors (20%). After antibiotic treatment of the tissue, microorganisms could still be encountered in cryoprotective medium samples from 55 donors (20%). Most of the contaminants in these final samples were identified as Propionibacterium species and Corynebacterium species and had already been detected in the transport medium by the alternative validated culture method. Conclusions: The use of blood culture flasks for microbiological assessment of non-blood liquid media and the cultivation of myocardial tissue fragments may hamper detection of certain microorganisms and therefore provide less complete information about microbiological safety. Heart Valve Banks may want to review their microbiological examination and decontamination procedures regarding the ability to detect and eliminate anaerobic skin flora, respectively.