Are Antibiotics Effective Against Fusarium and Aspergillus?

Abstract

Purpose: : Given published reports of fungal keratitis which improved with antibiotic treatment alone, we tested the susceptibility of Fusarium and Aspergillus isolated from keratitis to amoxicillin, cefazolin, chloramphenicol, moxifloxacin, tobramycin, and benzalkonium chloride (BAK).

Methods: : 10 isolates of Fusarium and 10 isolates of Aspergillus from cases of fungal keratitis at Aravind Eye Hospital in South India were tested using microbroth dilution for susceptibility to amoxicillin, cefazolin, chloramphenicol, moxifloxacin, tobramycin, and BAK. For each combination of agent and organism, the MIC₅₀ and MIC₉₀ were determined.

Results: : BAK had the lowest MIC for both Fusarium (MIC₅₀ = 32 µg/ml, MIC₉₀ = 64 µg/ml) and Aspergillus (MIC₅₀ and MIC₉₀ = 16 µg/ml). Chloramphenicol had activity against both Fusarium (MIC₅₀ = 1000 µg/ml, MIC₉₀ = 2000 µg/ml) and Aspergillus (MIC₅₀ = 2000 µg/ml, MIC₉₀ = 4000 µg/ml), while moxifloxacin and tobramycin had activity against Fusarium but not Aspergillus. For Fusarium, moxifloxacin had a MIC₅₀ = 1000 µg/ml and MIC₉₀ = 2000 µg/ml, while tobramycin had a MIC₅₀ = 500 µg/ml and MIC₉₀ = 700 µg/ml. For comparison, we found that amphotericin B had a MIC₅₀ of 0.5 µg/ml for both Fusarium and Aspergillus.

Conclusions: : The susceptibility of Fusarium to tobramycin, moxifloxacin, chloramphenicol, and BAK and of Aspergillus to chloramphenicol and BAK may explain anecdotal reports of fungal ulcers which improved with antibiotic treatment alone. In some cases, the antibiotic MICs were lower than the typically prescribed concentrations, especially for tobramycin which can be given in a fortified concentration of 14,000 µg/ml. The low concentration of BAK found in some antibiotic eyedrops may also be beneficial. Regardless, the MICs of antibiotics are not in the range of antifungal agents such as natamycin, amphotericin B, or voriconazole. Antibiotics may, however, have some effect on Fusarium and Aspergillus when used as initial treatment prior to identification of the pathologic organism.

Keywords: antibiotics/antifungals/antiparasitics • fungal disease • keratitis