Biguanide‐induced changes in Acanthamoeba castellanii: an electron microscopic study

• Published in: Journal of applied microbiology 1998, Vol.84 (1), p.53-62
• Main Authors: KHUNKITTI, W, HANN, A. C, LLOYD, D, FURR, J. R, RUSSELL, A. D
• Format: Article
• Language: English
• Subjects: Acanthamoeba - drug effects; Acanthamoeba - physiology; Acanthamoeba - ultrastructure; Acanthamoeba castellanii; Acanthamoeba Keratitis - prevention & control; Animals; Bacteriology; Biguanides - pharmacology; Biological and medical sciences; Biology of microorganisms of confirmed or potential industrial interest; Biotechnology; Cell Membrane - drug effects; Cell Membrane - ultrastructure; chlorhexidine; Chlorhexidine - pharmacology; cytoplasm; Cytoplasm - drug effects; Cytoplasm - ultrastructure; Disinfectants - pharmacology; Fundamental and applied biological sciences. Psychology; Humans; Life Cycle Stages; mechanism of action; Microbiology; Microscopy, Electron; Microscopy, Electron, Scanning; Mission oriented research; Morphology, structure, chemical composition; Physiology and metabolism; plasma membrane; scanning electron microscopy; shrinkage; trophozoites; ultrastructure
• ISSN: 1364-5072; 1365-2672
• DOI: 10.1046/j.1365-2672.1997.00305.x

Trophozoites and cysts of Acanthamoeba castellanii were exposed to chlorhexidine diacetate (CHA) and polyhexamethylene biguanide (PHMB); changes in cell ultrastructure and surface structure were examined by both transmission and scanning electron microscopy. PHMB caused a greater degree of structural and membrane damage; the cytoplasmic contents were severely depleted and there were clusters of densely stained precipitates on the cell surface. Concentrations of CHA greater than 100 μg ml−1 produced shrinkage from the cyst wall. At high concentrations, PHMB induced a slight withdrawal of the cytoplasm from the wall and, unlike CHA, induced swelling of the cysts. These findings do not define the mechanisms of action of CHA and PHMB, but provide evidence that a major target site for both agents is the plasma membrane. However, additional intracellular damage undoubtedly contributes to the lethal effects. The greater resistance of cysts may be associated with reduced biguanide uptake.