Viability and nematophagous activity of the freeze-dried fungus Arthrobotrys robusta against Ancylostoma spp. infective larvae in dogs

Viability and in vitro and in vivo activities of freeze-dried conidia of the predatory fungus Arthrobotrys robusta (I-31) were evaluated against infective larvae (L3) of Ancylostoma spp. in dogs. A. robusta conidia were lyophilized and stored at 4 °C for a month. Freeze-dried conidia were diluted to 1 × 103 conidia/ml and tested in vivo. The treated group consisted of a solution containing conidia (1 ml) and 1000 Ancylostoma spp. (L3) placed on Petri dishes plated with 2% water-agar (2% WA), at 25 °C, in the dark for 10 days. The control group consisted of 1000 Ancylostoma spp. L3, plated on 2% WA. After 10 days, Ancylostoma spp. L3 from both the treated and the control groups were recovered and counted. The in vivo test was performed on two dogs by administering a single oral dose of freeze-dried conidia (1.5 × 105) in aqueous solution to one animal and only water to the other. Fecal samples were collected at 12, 24 and 48 h after the treatments, plated 2% WA plates and incubated at 25 °C for 15 days. A thousand Ancylostoma spp. L3 larvae were spread on these plates. At day 15, infective L3 recovered from the treated and control groups were counted. In the in vitro test, A. robusta was able to survive the freeze-drying process, grow in the plates, form traps and capture Ancylostoma spp. L3. There was a 75.38% decrease in the number of infective larvae recovered from the treated group. The in vivo test showed that freeze-dried A. robusta conidia survived the passage through the gastrointestinal tract of the treated dog, was able to grow in the plates and capture Ancylostoma spp. L3, reducing the number of recovered L3 (p < 0.01). Freeze-drying can be an alternative method for conservation of conidia of nematophagous fungi.