Abstract
Acanthamoebae success as human pathogens is largely due to the highly resistant cysts which represent a crucial problem in treatment of Acanthamoeba infections. Hence, the study of cyst wall composition and encystment play an important role in finding new therapeutic strategies. For the first time, we detected high activity of cytoskeletal elements – microtubular networks and filamentous actin, in late phases of encystment. Cellulose fibrils – the main components of endocyst were demonstrated in inter-cystic space, and finally in the ectocyst, hereby proving the presence of cellulose in both layers of the cyst wall. We detected clustering of intramembranous particles (IMPs) and their density alterations in cytoplasmic membrane during encystment. We propose a hypothesis that in the phase of endocyst formation, the IMP clusters represent cellulose microfibril terminal complexes involved in cellulose synthesis that after cyst wall completion are reduced. Cyst wall impermeability, due largely to a complex polysaccharide (glycans, mainly cellulose) has been shown to be responsible for Acanthamoeba biocide resistance and cellulose biosynthesis pathway is suggested to be a potential target in treatment of Acanthamoeba infections. Disruption of this pathway would affect the synthesis of cyst wall and reduce considerably the resistance to chemotherapeutic agents.
Highlights
Species of free-living amoebae genus Acanthamoeba Volkonsky, 1931 are opportunistic unicellular parasites with worldwide distribution in diverse environments including freshwater, soil, man-made habitats and even clinical settings[1–4]
The silver impregnation considerably enhanced the visibility of circular ostioles (5–9 per one cyst in A. lugdunensis, 3–5 per one cyst in A. quina) along with their opercula (Fig. 1B,G)
The cyst wall in both A. lugdunensis and A. quina is characteristic with the absence of superficial reticulation which can be demonstrated by silver impregnation method in some species of the Group II (e.g. A. castellanii)[20]
Summary
Species of free-living amoebae genus Acanthamoeba Volkonsky, 1931 are opportunistic unicellular parasites with worldwide distribution in diverse environments including freshwater, soil, man-made habitats and even clinical settings[1–4]. Group II consists of species with cysts usually with diameter up to 18 μm with wrinkled ectocyst and stellate, polygonal, triangular, or oval endocyst, closely apposed or widely separated. This group includes the majority of described species and the majority of species associated with human infections. The present classification of the genus Acanthamoeba is based on 18S rDNA and includes 21 genotypes to date (T1–T21), from which the most frequently associated with human infections is the T4 genotype[21–23] Both the classification approaches are not well coordinated, the morphological classification has proved useful in interpreting molecular clustering of Acanthamoeba isolates[24].
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