In vitro effect of Chrysosporium indicum and Chrysosporium keratinophylum on Toxocara canis eggs

Abstract

The degree of antagonism exercised by fungi on geohelminth development varies according to the morphological alterations caused by different fungal species. Saprophytic fungi may exert ovicidal or ovistatic effects. The aim of this study was to apply scanning electron microscopy (SEM) to observe the action of two soil saprophytic species of Chrysosporium (C. indicum and C. keratinophylum) on Toxocara canis eggs. The fungal strains to be tested were incubated for 28 days at 28°C in 2% water agar with a suspension of unembryonated T. canis eggs. A suspension of T. canis eggs in 2% water agar was used as control group. The assay was done in triplicate for each fungus and the control group. SEM observations were performed on the 4th, 7th, 14th, 21st, and 28th day after inoculation. The effect of the fungi on eggs was evaluated in accordance with the alterations observed on the surface and the changes in the normal characteristics of the eggs. Hyphae around the eggs, appresoria penetrating the shell and changes in the typical egg membrane were observed in this assay. Type 3 effect (alterations that occur both in the embryo and the shell, and hyphal penetration of the eggs) was the prevalent effect. SEM allowed us to observe clearly the morphological alterations in T. canis eggs due to the effect of C. indicum and C. keratinophylum. Both saprophytic species of Chrysosporium alter the egg structure and alterations increase as exposure increases.

Keywords: Actividad ovicida; Biological control; Control biológico; Geohelminths; Geohelmintos; Hongos nematófagos; Nematophagous fungi; Ovicidal activity.