False negative results in tissue banking: the 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.
Twenty-four corneal tissues were retrieved by the personnel of the Eye Bank of Monza (Italy) and transported to the bank in Eusol-C (AL.CHI.MI.A. Srl, Italy). Tissues were transferred to Tissue-C (AL.CHI.MI.A. Srl, Italy), stored for 12-14 days at 31°C and then placed in the deswelling/transport medium Carry-C (AL.CHI.MI.A. Srl, Italy) for 24 h at room temperature.
Microbiological analyses were performed pre-processing on Eusol-C and post-processing on Tissue-C and Carry-C by the Eye Bank of Monza, according to bank standard procedures using BACTEC plus aerobic/anaerobic; in parallel, microbiological analysis 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).
Pre-processing microbiological analysis of the media, showed that 75% of the samples were contaminated (Staphylococcus spp.). 25% of such contaminations were not detected by BACTEC, thus yielding false negative results.
45% of the samples remained positive at the end of the process. 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 of the media.
The presence of contaminants in the media at the end of the storage process indicates that standard corneal storage media do not guarantee efficient decontamination of donor corneas.