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.
RESUMEN
Purpose: To evaluate the efficacy of voriconazole and amphotericin B in McCarey–Kaufman (MK) media. Methods: MK media vials were supplemented with either voriconazole at 1, 2, 20, 50, 100 ?g/mL or amphotericin B at 0.5, 1, 2, 10, 20 ?g/mL. The standard inoculum of the American Type Culture Collection (ATCC) strain of Candida albicans, Aspergillus flavus, and Fusarium keratinoplasticum was added to the set of vials. The efficacy outcomes were calculated as ‘viable fungal colony counts’ determined from the samples taken on Days 0 and 4. MK media containing fungal inoculum but without antifungal supplements were used as control. Results: In the voriconazole arm, on Day 4, a reduction in the colony count was observed for Candida albicans (1 ?g/mL, 36%; 100 ?g/mL, 100%), Aspergillus flavus (1 ?g/mL, 53.8%; 100 ?g/mL, 80.4%), and Fusarium keratinoplasticum (1 ?g/mL, 39.0%; 100 ?g/mL, 72.2%). Similarly, in the amphotericin B arm, on Day 4, a reduction in the colony count was observed for Candida albicans (0.5 ?g/mL; 99.9%; 20 ?g/mL, 100%), Aspergillus flavus (0.5 ?g/mL, 65.2%; 20 ?g/mL, 84.8%), and Fusarium keratinoplasticum (0.5 ?g/mL, 90.1%; 20 ?g/mL, 100%). Conclusion: Compared to voriconazole, the addition of amphotericin B significantly reduces fungal contamination in MK media.