False negative results in microbiological analyses of corneal tissues EEBA 2014

Introduction: Corneal culture media contain antibiotics that might interfere with microbial growth during microbiological analysis and consequently result in false negatives.

Purpose: The aim of the study was to investigate the effects of antibiotic residues on microbiological analyses of donor corneas after culture in eye bank.

Material and methods: Sixty-one corneal tissues retrieved by the personnel of the eye banks were transported to the bank in EUSOL-C (AL.CHI.MI.A. S.r.l., Italy) and evaluated according to standard eye bank procedures. The tissues were then transferred to TISSUE-C (AL.CHI.MI.A. S.r.l., Italy) for tissue culture at 31°C for 12-14 days.
Microbiological analyses of the culture media were performed by the eye banks at the end of the culture, using BacTEC plus aerobic/anaerobic system (BD, Germany), according to bank standard procedures. The same culture media were sampled and analysed by R&D AL.CHI.MI.A using the RESEP tube device (AL.CHI.MI.A. S.r.l, Italy) that allows to remove the antibiotics from samples undergoing the test.

Results: Microbiological analyses with the RESEP tube showed that 59% of samples were contaminated on average. The percentage of positive results varied depending on the eye bank. None of these contaminations was detected by the BacTEC system.

Conclusions: Removal of antibiotic residues from corneal storage media with the ResEP tube resulted in a significant number of false negatives in the microbiological analyses.
The presence of contaminants in the media at the end of the storage process indicates that standard corneal storage media do not guarantee efficient corneal decontamination.