False negative results in microbiological analyses of corneal tissues

Abstract: The use of antibiotic cocktails during corneal processing can lead to an antibiotic carry-over effect, which in turn can generate false negative results in microbiological analysis. The aim of the study was to investigate the impact of antibiotic residues on microbiological analyses of organ cultured donor corneas.
The study performed by two Italian Eye Banks and AL.CHI.MI.A.’s R&D Dept. on sixty-one corneal tissues unsuitable for transplantation.
The corneal tissues retrieved by the personnel of the eye banks were transported to the bank in Eusol-C (AL.CHI.MI.A. Srl, Italy), transferred to Tissue-C (AL.CHI.MI.A. Srl, Italy) and stored for 12-14 days at 31°C.
Microbiological analyses were performed post-processing on Tissue-C by the eye banks, according to bank standard procedures using BACTEC plus aerobic/anaerobic system (BD); in parallel, microbiological analyses were performed by AL.CHI.MI.A. with sterility test according to the European Pharmacopeia after removing potential interfering antibiotics with RESEP (AL.CHI.MI.A Srl, Italy).
Sterility test after removal of interfering antibiotics with RESEP showed 59% of positive (contaminated) samples on average at the end of the process; the percentage of positive results varied depending on the bank. None of these contaminations was detected by BACTEC.
Removal of antibiotic residues from corneal storage media with RESEP resulted in a significant number of false negative results in the microbiological analyses.
The presence of contaminants in the media at the end of the storage process indicates that standard corneal storage media does not guarantee efficient corneal decontamination.