36 Cornea microbiology contamination rate depending on post mortem time, retrospective analysis at croatian tissue and cell bank, UHC Zagreb.

Background: Corneas procured post mortem are at risk of microbiology contamination, therefore decontamination procedures before storage, aseptic techniques during processing and antimicrobials used in the storage medium are routinely used. Despite that, corneas are discarded due to microbiology contamination. According to professional guidelines, corneas can be procured preferably within 24 hours after cardiac arrest but up to 48 hours. Our goal was to evaluate the risk of contamination depending on the post mortem time and the spectrum of microbes isolated.
Methods: Corneas were decontaminated before procurement using 0,5% povidone iodine and tobramycin, stored in the organ culture medium and microbiologically tested after four to seven days of storage. Ten millilitres of cornea preservation medium were inoculated in two blood bottles (aerobic, anaerobic/fungi, Biomeriex) and incubated for seven days.Microbiology testing results in the period of four years (2016-2020) were retrospectively analysed. Corneas were divided in four groups depending on the duration of post mortem interval: group A post mortem interval < 8 h, group B post mortem ranging from 8 to 16 h, group C post mortem ranging from 16 to 24 h and group D post mortem > 24 h. Contamination rate and spectrum of isolated microorganisms in all four groups were analysed.
Results: 1426 of 2019 procured corneas were stored in organ culture and microbiologically tested. 65/1426 of tested corneas were contaminated (4,6%). In total, 28 strains of bacteria and fungi were isolated.Contamination rate of post mortem groups are as following: group A 3,1% (14/455), group B 4,1% (23/561), group C 6,7% (27/402) and group D 12,5% (1/8).In the group A bacteria family Staphylococcaceae, Moraxellaceae, Morganellaceae were predominately isolated (64,3%). In the group B fungi Saccharomycetaceae, bacteria Moraxellacea, Staphylococcaceae, Morganellaceae and Enterococcaceae were predominately isolated (78,1%). In the group C, bacteria family Enterococcaceae, Moraxellaceae and fungi Saccharomycetaceae are most often isolated (70,3%). In the group D bacteria family Enterobacteriaceae was isolated (100%).
Conclusion: Organ culture allows detection and discard of microbiology contaminated corneas. Our results show higher microbiology contamination rate for corneas with longer post mortem intervals, suggesting these contaminations can be rather related to donor post mortem changes and contamination than previous infection. In order to keep the best quality and safety of the donor cornea, all efforts should be directed in disinfection of the cornea and keeping post mortem interval shorter.
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