Microbiological profile of donor corneas: a retrospective study from an eye bank in north India.

Purpose: To study the microbiological profile and the antibiotic sensitivity of the microorganisms cultured from donor corneas and evaluate with respect to the decontamination protocols during the study period.
Methods: Retrospective review of microbiological culture reports of 2,291 donor eyes sent from January 2000 to December 2003. Donor corneas were treated with 0.4% gentamicin (phase I), 1% povidone-iodine and 0.4% gentamicin (phase II), and 5% povidone-iodine with 0.4% amikacin (phase III). Limbal swabs taken by the eye bank technician after antimicrobial decontamination of donor eyes and sent to the microbiology laboratory for culture were tracked. The positive culture reports with antibiotic sensitivity pattern were studied and results correlated with decontamination protocols.
Results: Staphylococcus epidermidis, Pseudomonas aeruginosa, and Alkaligenes faecalis were the 3 most common isolates overall. The percentage of positive bacterial cultures reduced when we used 5% povidone-iodine and 0.4% amikacin (31.3%) as compared to 1% povidone-iodine and 0.4% gentamicin (61.8%) (P < 0.001). Addition of povidone-iodine decreased positive fungal cultures from 6% in phase I to 2.2% in phase II (P < 0.01) and 1.9% in phase III (P < 0.01). Amongst the total bacterial cultures sent after antimicrobial treatment, Gram-positive bacteria decreased from 38.6% (64/166) in phase I to 27.6% (402/1457) and 10.8% (72/668) in phases II and III, respectively (P < 0.001), and Gram-negative bacteria increased from 10.2% (17/166) to 18.8% (274/1457) and 19.8% (132/668), respectively (P = 0.02). Amongst the positive bacterial cultures, the proportion of Gram-positive bacteria decreased from 79.0% (64/81) in phase I to 59.5% (402/676) and 35.3% (72/204) in phases II and III, respectively (P < 0.001), and that of Gram-negative bacteria increased from 21.0% (17/81) to 40.5% (274/676) and 64.7% (132/204), respectively (P < 0.001).
Conclusions: Different combinations of antimicrobials failed to eliminate all organisms, especially Gram-negative bacteria from the donor corneal surface. The increase in proportion of Gram-negative bacteria despite the use of amikacin combined with povidone-iodine suggests a need to find a better combination for decontamination of donor corneal tissue.