Single-cell force spectroscopy of Giardia duodenalis trophozoites revealed a unique attachment mode compared to other eukaryotic cells

Introduction: The unicellular parasite Giardia duodenalis is the causative agent of giardiasis, a gastrointestinal disease with global spread. Disease initiation is provoked by adhesion between G. duodenalis and the human intestinal epithelium. A unique microtubule-based attachment organelle, the cup-shaped ventral disc, facilitates this process. However, the detailed physical function of the ventral disc is still debated. In this study, we investigate adhesion forces involved during attachment of single G. duodenalis trophozoites, in comparison to adhesion mechanisms of the opportunistic pathogen Candida albicans and spreading human keratinocytes.

Material & Methods: Single cell force spectroscopy, based on fluidic force microscopy (FluidFM) was used to investigate the adhesion parameters of G. duodenalis trophozoites adhering to a flat glass surfaces. Comparison were made with the aforementioned cell types.

Results: Force-distance curves displayed novel and so far undescribed characteristics for a microorganism, namely, gradual force increase on the pulled trophozoite, with localization of adhesion force shortly before cell detachment length. Adhesion forces reached 7.7 ± 4.2 nN at 1 µm/s pulling speed. Importantly, this unique force pattern was different from the saw-tooth pattern of Candida albicans and from the long cell interaction length of spreading keratinocytes, both considered for comparison in this study. Furthermore, the attachment mode of G. duodenalis trophozoites was mechanically resilient to tensile forces when pulling speeds were increased to 10 µm/s while adhesion forces rose to approximately 28.7 nN.

Conclusions: Comparative force spectroscopy revealed novel and unique retract force curve characteristics for attached G. duodenalis trophozoites, suggesting a ligand-independent suction or clutching mechanism that substantially differs from other well-described microbial adhesion strategies.