RESUMEN
Purpose: To curtail the potential of donor corneal tissue disseminating fungi to the recipient抯 eye, we evaluated the addition of amphotericin B to McCarey?Kaufman (M?K)梒orneal storage medium supplemented with colistin. Methods: Amphotericin B was examined for its ability to inhibit the growth of Candida albicans and Aspergillus flavus using a microbroth dilution test and checkerboard assay in combination with only gentamicin and a combination of colistin, gentamicin, and amphotericin B. The safety on epithelium and endothelium was evaluated by 3?(4,5?dimethylthiazol?2?yl)?2, 5?diphenyltetrazolium bromide (MTT) assay. Results: The minimal inhibitory concentration of gentamicin was found to be >256 ?g/ml against both C. albicans and A. flavus, whereas that of amphotericin B was found to be in a range of 0.25�5 and 1�?g/ml for C. albicans and A. flavus, respectively. According to the checkerboard assay, 80% (4/5) of C. albicans isolates and 100% (5/5) of A. flavus isolates responded synergistically to the combination of amphotericin B and gentamicin, but only 20% (1/5) of C. albicans isolates showed an additive effect. None of the tested isolates displayed antagonism. The combined effect of the three drugs also did not display any antagonistic effect. Additionally, the MTT assay reveals no toxic effect of the antimicrobials used on corneal epithelial and endothelial cells. Conclusion: In vitro experiments demonstrate that amphotericin B is not toxic to either epithelium or endothelium and is a promising additive to the M?K medium supplemented with colistin.
RESUMEN
Purpose: To assess the efficacy of the addition of polymyxin E (colistin) in the McCarey-Kaufman (MK) corneal storage solution against multi-drug resistant strains of Enterobacteriaceae, Staphylococcus aureus, and Candida spp. Methods: A standard micro broth dilution test and a checkerboard assay were performed for five multi-drug resistant (MDR) clinical strains of P. aeruginosa and five clinical strains of methicillin-resistant S. aureus (MRSA) and C. albicans against colistin and gentamicin alone and in combination. The minimum inhibitory concentration (MIC) and the fractional inhibitory concentration index (FICI) were calculated to assess the efficacy of each combination. Results: The MIC of colistin was in the range of 1–2 ?g/mL for P. aeruginosa, whereas it was 256–1024 ?g/mL against S. aureus. In comparison, the MIC of gentamicin was found to be 0.5–512 ?g/mL and 0.5–8 ?g/mL against P. aeruginosa and S. aureus, respectively. All five isolates of C. albicans did not exhibit any susceptibility to either colistin or gentamicin even at a concentration of ? 512 ?g/ mL each. The checkerboard assay was performed to evaluate the nature of the interaction of the combination of colistin and gentamicin. Based on the FICI, it was observed that the colistin and gentamicin combination has a maximum synergistic effect (FIC <0.5) in 80% (4/5) for S. aureus isolates, whereas the maximum additive effect (FIC >0.5–4) was 100% (5/5) for P. aeruginosa and the minimum additive effect was 20% (1/5) for S. aureus isolates. Antagonism (FIC ? 4) was not observed in any combination between the strains used in the study. Both colistin and gentamicin alone or in combination were, however, ineffective against Candida spp. Conclusion: The addition of colistin has an inhibitory effect on bacterial contamination that could be possibly caused by MDR strains and could potentially be considered as an additional additive in corneal storage media.