Evaluation of different microbiological testing methods in tissue banking

Abstract: Each tissue bank validates its own method for microbiological analysis of tissues, which is essential to determine whether they can be released for transplantation.
The aim of the study was to compare the results of microbiological analyses of tissues intended for transplantation obtained by using different microbiological testing methods.
Human cardiovascular tissues, skin and corneas were retrieved and processed by five different tissue banks. Tissues were decontaminated at 4°C for 24h/72h (cardiovascular) or at 22°C for 90 min. (skin) either with bank prepared solutions or BASE.128 (AL.CHI.MI.A. Srl., Italy) and then cryopreserved in RPMI 1640 with the addition of 10% DMSO. Corneas were processed and stored under organ culture conditions. Microbiological analysis of tissues and processing liquids were performed by tissue banks according to their standard procedures, using BacT/ALERT, BACTEC and direct inoculation of culture media (Thioglycollate/TSB); samples were tested in parallel at AL.CHI.MI.A. with the sterility test according to European Pharmacopoeia (EP), with the removal of antibiotic residues with RESEP.
All bacteriological analyses of decontaminated cardiovascular tissues performed with direct inoculum method resulted negative. 3% of liquid and tissue samples were found positive with the BACTEC method. The percentages of positive liquid and tissue samples with RESEP were 16% and 25%, respectively.
The bacteriological analysis of decontaminated skin samples were negative with both BACTEC and direct inoculum method. 33% of liquid samples and 50% of tissue samples were found positive using RESEP.
Corneas processing liquids resulted negative with BACTEC and direct inoculum method. Instead, 59% of the samples resulted positive with RESEP and sterility test according to EP.
Different results were obtained depending on the used method to perform microbiological analyses after tissue decontamination. A validation of the microbiological method, including accurate removal of possible antibiotic residues in decontaminated tissue and processing liquid is necessary to ensure the safety of tissue allografts.