Antimicrobial effect of cryopreservation on donor ocular tissue

The aim of this study was to assess the antimicrobial effect of cryopreservation on donor globes with a previously positive culture. More specifically, our study aims at determining whether microbial organisms can still be cultured after cryopreservation in previously culture positive donor whole globes.

This is a prospective quality assurance study of microbiological cultures using donor ocular tissues obtained by the Lions Eye Bank of Manitoba and Northwestern Ontario from January 2009 to January 2010. Enucleated globes were soaked in 2.5% povidone iodide for 5 minutes, rinsed with sterile normal saline, and cultured in chocolate and Sabouraud agar and thioglycolate broth. The whole globes were then preserved in Optimyxin Plus and an antibiotic solution before being cryopreserved for 1 month. Culture-positive whole globes were thawed to room temperature and recultured on the same media to determine the effect of the cryopreservation protocol of our eye bank on bacterial counts.

Twenty-seven donor whole globes were included in our study. Upon primary culture, all specimens had positive bacterial growth. The most common isolate on primary culture was coagulase-negative Staphylococcus (62.8%). Upon secondary culture of the thawed cryopreserved whole globes, no bacterial growth was detected on any of the culture media.

Our study demonstrates that harvested donor whole globes with positive microbial cultures became culture negative after secondary culture by the Lions Eye Bank of Manitoba and Northwestern Ontario's cryopreservation protocol. This suggests that ocular tissues treated in this manner may be microbiologically safe and therefore able to be used for transplantation in patients.