Finding the Minimum Inhibitory Concentrations of Amphotericin B for various strains of Candida

In the United States of America, corneal tissues from deceased donors are stored in cold storage fluids that do not contain antimycotics, and undergo tissue processing for the new lamellar techniques as soon as possible after tissue procurement; therefore, in case of donor-derived infections in recipients, the only option is the treatment of the transplanted patient.

Whether the increased trend of post-keratoplasty fungal infection during the recent years in the USA might be due to the absence of antimycotic agents in the cold media or to an easier infiltration of infectious organisms in the lamellar interspaces during tissue processing, the possibility of supplementing cold storage media with antimycotic agents is attracting increasing attention as a possible solution to increase recipients’ safety.

A recent in vitro time-kill study conducted by the Alchilife R&D team on a new medium containing Amphotericin B (2.5 µg/ml) and intended for cold storage of explanted corneas demonstrated the antimycotic efficacy of the medium – despite the low temperature – against fungal strains commonly associated with keratitis and endophthalmitis, including C. albicans, C. glabrata, and C. tropicalis.

In parallel with the time-kill study, the Amphotericin B Minimum Inhibitory Concentration (MIC) for these Candida strains was also determined. By using the Etest strips containing a concentration of Amphotericin B varying from 0.002 to 32 µg/ml that was placed over each yeast strains, individually cultured on agar plates, for 24 and 48 hours, the MICs were found to vary between 0.25 and > 1 µg/ml.

These results suggested that the differences in the killing efficacy among strains may correspond to the different susceptibility to Amphotericin B according to the MICs; not less importantly, they also confirmed the good antifungal efficacy of Amphotericin B in the new product for cold storage, since the 2.5 µg/ml concentration is well above the so-determined MIC values.

References:

• Aldave AJ et al. Report of the Eye Bank Association of America medical advisory board subcommittee on fungal infection after corneal transplantation. Cornea 2013; 32:149–154
• Giurgola L. et al. Antimycotic efficacy and safety of a new cold corneal storage medium by time-kill and toxicity studies. Cornea 2019; 38(19):1413-1321.
• Fontana L. et al. Interface infectious keratitis after anterior and posterior lamellar keratoplasty. Clinical features and treatment strategies. A review. Br J Ophthalmol 2018; 0:1–8