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M. Hermel, S. Salla, N. Hamsley, A. Steinfeld; Probability of Detecting Contamination in Organ Cultured Donor Corneas With Repeated Testing - Implications for Allocation Routine. Invest. Ophthalmol. Vis. Sci. 2009;50(13):2189.
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© ARVO (1962-2015); The Authors (2016-present)
Corneas harvested post-mortem are at risk of contamination, therefore antibiotic additives are used in cold storage and organ culture systems. In the latter, sterility testing of the medium is part of the standard protocol. Intuitively, testing after longer organ culture periods should be more likely to detect contaminations than early testing, but may delay allocation. This study uses longitudinal test and retest data from our cornea bank to evaluate whether an optimal time for detection of donor cornea contamination can be identified.
The study complies with the Declaration of Helsinki. All procedures were supervised using a certified quality management system (ISO 9001:2000). 675 donor corneas harvested by enucleation or corneoscleral excision over 4.5 consecutive years were processed according to German and EC laws and guidelines. The corneas were stored in a closed organ culture system in 100ml MEM plus antibiotics/antimycotics at 31°C for up to 28 days without media exchange. 10ml samples of medium were obtained between day 3 and 8 of culture and tested for sterility in an automated detection system (BacT/ALERT, bioMérieux). In 359 corneas, a second sterility test was performed from the same medium before release. Contamination detection probabilities were evaluated with regard to the date of the primary test.
Overall, 18 contaminations were found. Contaminations were bilateral in 4 donors. One contamination was apparent in the medium prior to the primary sterility test, 11 were detected upon primary sterility testing. Furthermore, 6 primarily undetected contaminations were observed, 5 in the secondary sterility test, 1 suspected microscopically. In most cases, contamination could also be seen by medium turbidity and acidification, but in 3 cases macroscopic medium changes were significantly delayed or absent. No correlation was found between the time of primary sterility test and both positive and false negative test outcomes.
Detection probability of organ culture media contamination does not increase between days 3 and 8. The recommended follow-up after sterility testing is 7 days. Corneas can thus be allocated after 10 days of organ culture. Nevertheless, the testing it is not 100% sensitive, and should always be combined with macroscopic inspection of the media.
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