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Updated: Apr 23, 2026

Visualizing Bacteria in Nematodes using Fluorescent Microscopy

Visualizing Bacteria in Nematodes using Fluorescent Microscopy

Published on: October 19, 2012

Cyclotide interactions with the nematode external surface.

Michelle L Colgrave¹, Yen-Hua Huang, David J Craik

¹University of Queensland Institute for Molecular Bioscience, Brisbane, Australia.

Antimicrobial Agents and Chemotherapy

|March 10, 2010

Summary

This summary is machine-generated.

Cyclotides, cyclic plant peptides, are toxic to gastrointestinal nematodes like Haemonchus contortus by increasing membrane permeability. This surface interaction, not ingestion, causes toxicity in both larval and adult worms.

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Area of Science:

Biochemistry
Parasitology
Molecular Biology

Background:

Cyclotides are cyclic peptides with a cystine knot structure found in plants.
They exhibit anthelminthic activity against important sheep gastrointestinal nematodes, Haemonchus contortus and Trichostrongylus colubriformis.
The precise mechanism of cyclotide action against nematodes is not fully understood.

Purpose of the Study:

To investigate the interaction of the cyclotide kalata B1 with the external surface of Haemonchus contortus.
To determine if cyclotide toxicity requires ingestion or if surface interaction alone is sufficient.
To elucidate the mechanism by which cyclotides exert their toxic effects on nematodes.

Main Methods:

Studied the toxicity of kalata B1 on H. contortus adult worms with pharyngeal ligatures.
Assessed cyclotide toxicity on nonfeeding larval stages.
Measured tritiated inulin uptake in ligated adult worms.
Utilized polyethylene glycols of various sizes in toxicity and hemolytic assays.

Main Results:

Cyclotides are toxic to H. contortus regardless of ingestion, indicating surface interaction is sufficient.
Kalata B1 increased the permeability of the external membranes of adult nematodes.
Polyethylene glycols protected larval stages and inhibited cyclotide-induced hemolysis, suggesting pore formation.
Cyclotides likely interact with the lipid-rich epicuticle layer of the nematode surface.

Conclusions:

Cyclotides exert their anthelminthic effects through direct interaction with the nematode's external surface, primarily the epicuticle.
The mechanism involves the formation of pores in the nematode's outer membranes, leading to increased permeability and toxicity.
This surface-mediated toxicity is effective against both larval and adult stages of H. contortus.