In Vitro Evaluation of Nematodicidal Bacteria Isolated from Cow Dung Against Strongyle Nematodes of Small Ruminants

A study was carried out to identify the nematodicidal bacteria in ruminant dung and assess their efficacy against gastrointestinal nematodes of small ruminants. A total of 10 bacteria were isolated from ruminant dung and their nematodicidal activity was determined. Evaluation of nematodicidal efficacy of all the isolates through larval feeding assay revealed 0.00 ± 0.00 to 100.00 ± 0.00% efficacy with varying time. However, of the 10 bacterial isolates from the dung, three bacterial isolates showed 100.00 ± 0.00% nematodicidal activity in 4 h of incubation. The bacterial isolates were preliminarily classified based on cultural and Gram-staining characteristics and were subsequently identified by 16S rRNA gene sequencing. Molecular analysis confirmed that the three isolates exhibiting the highest nematodicidal activity in the larval feeding assay were Citrobacter amalonaticus, Shigella flexneri, and Klebsiella aerogenes. The isolate Citrobacter amalonaticus (5.5 × 108 CFU per mL) caused 100% larval mortality at 10 and 7.5% culture broth concentrations in 4 and 6 h of incubation, respectively in a dose-dependent larval assay. In the simulation pasture model study, compared to the control tray, the pasture tray treated with the bacterium Citrobacter amalonaticus (5.6 × 108 CFU per mL) showed a reduction in larval recovery of 87.50%. The present work using bacteria isolated from animal origin against nematodes affecting small ruminants is the first of its kind in India. The results of this seminal work will go a long way in developing an alternative strategy for chemical control of the worm problem in animals.