Ketoconazole Inhibits the Growth and Development of Ichthyophonus sp (Mesomycetozoa) In Vitro

We determined the in vitro effect of the azol-derivative antifungal ketoconazole (KZ) on the morphology, growth, and development of teleost fish parasite Ichthyophonus sp. The KZ was delivered to culture medium using liposomes (L) or a lipid emulsion (E) at five different doses (i.e. 5, 50, 100, 200, and 400 mg/ml) for both L and E formulations. Controls consisted of Eagle's minimum essential medium (MEM) supplemented with 10% foetal bovine serum (MEM-10) alone (C-MEM) or containing amounts of L or E equivalent to those used in the KZ100 and KZ400 treatments (i.e. 100L, 400L, 100E, and 400E, respectively). Morphological alterations, such as a decrease in the number of dividing spores and nuclei, and condensation or even destruction of the cytoplasm, were observed using light and electron microscopy in the MEM-cultured organisms receiving KZ formulations, especially with KZ400L preparations, at both 7- and 14-d postinoculation. The KZ treatments also demonstrated a statistically significant inhibition of Ichthyophonus growth in MEM. These treatments also had an inhibitory effect on subsequent Ichthyophonus germination in Earle's fish saline agar (EFSA) medium, which was more evident for L formulations when the organism was treated for 7 d and for E formulations at 14 d. Our results endorse the potential use of KZ for the treatment for ichthyophonosis and provide support to proceed to in vivo assays.