Scanning electron microscopy of Ancylostoma spp. dog infective larvae captured and destroyed by the nematophagous fungus Duddingtonia flagrans
Introduction
Nematophagous fungi have been studied as an alternative for controlling several nematodes (Araújo et al., 1993, Nansen et al., 1996, Chandrawathani et al., 1998, Araújo and Guimarães, 2002, Oliveira et al., 2002, Castro et al., 2003).
The species Duddingtonia flagrans is an important nematode-trapping fungus that has been used as a biological control agent of the free-living stages of gastrointestinal parasites of domestic animals (Baudena et al., 2000, Paraud et al., 2005, Maciel et al., 2006, Rocha et al., 2007).
Since dog parasite helminths of the Ancylostoma genus have been requesting attention for their zoonotic potential (Soulsby, 1982, Schantz, 1991, Bahgat et al., 1999, Robertson et al., 2000, Prociv and Croese, 1996), the destruction of their infective stages by using nematophagous fungi may be an alternative for the control of animal parasitic nematodes under environmental conditions.
Thus, the characterization of the fungus × larvae interaction processes would be very important, once this interaction is beneficial to the nematophagous fungi but not to the nematode larvae. This could influence on the selection of promising fungal isolates which might be used in biological control programs (Mendoza-de-Gives, 1999). Despite the studies that have been carried out, there is little information on the ultrastructural aspects of the interaction between the fungus D. flagrans and the gastrointestinal parasite nematode infective larvae of domestic animals.
The scope of this study was to observe and understand the interaction processes between the nematode-trapping fungus D. flagrans (isolate CG768) against Ancylostoma spp. dog infective larvae (L3).
Section snippets
Acquirement of Ancylostoma spp. infective larvae
The Ancylostoma spp. L3 were obtained from fresh feces of naturally infected urban street dogs by means of vermiculite-coproculture kept for 10 days at 26 °C. At the end of the incubation period, the L3 were extracted by the modified Baermann's method, as described by Ueno and Gonçalves (1998). After 12 h, the sediment containing Ancylostoma spp. L3 was transferred to a centrifuge tube and washed with distilled water five times at 1000 rpm for 5 min. The supernatant was disposed at the end of each
Results
The initial formation of adhesive three-dimensional network traps, more robust than the vegetative hyphae, was observed 6 h after the Ancylostoma spp. L3 were added to the Petri's dishes with cellulose membrane colonized by the fungus D. flagrans (Fig. 1 A and B). The three-dimensional networks, spaced at intervals along the length of the vegetative hyphae, were found in the whole cellulose membrane surface probably due to the fact that the L3 were active and therefore dispersed on it (Fig. 1C).
Discussion
The methodology for the material preparation on cellulose membrane proposed by Nordbring-Hertz (1983) and Campos et al. (2008) for analysis under scanning electron microscopy showed to be applicable and efficient for both material recording and the study of the interaction between the nematode-trapping fungus D. flagrans against Ancylostoma spp. L3. The addition of 2% WA to the borders of the membrane prevented the Ancylostoma spp. L3 from going under the cellulose membrane and maintained it on
Acknowledgements
The authors would like to thank the Conselho Nacional de Desenvolvimento Científico e Tecnológico – CNPq for the research funding and scholarship granting, the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior – Capes for scholarship granting and Claúdia Alencar Vanetti of the Núcleo de Microscopia e Microanálise – NMM of the Universidade Federal de Viçosa – UFV, Brazil, for technical assistance.
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