Congo red effect on cyst viability and cell wall structure of encysting entamoeba invadens

Background. The cell wall of Entamoeba invadens cysts is composed of chitin microfibrils as the main structural component. It has been demonstrated in yeast that the chitin cell wall assembly is altered by dyes such as Congo red (CR) and Calcofluor. Methods. The purpose of this work was to study the cell wall assambly under the effect of CR dye on encysting E. invadens by means of light and electron microscopy, after the ammebas were subjected to the effect of 100-2,000 µg CR/mL. Experiments were performed either in BI-S-33 or in mLG media. Results. Trophozoit growth was not inhibited by 100-1,000 µg/mL CR after 8 days of incubation in BI-S-33 medium. However, low levels of growth were observed with 2,000 µg/mL of dye. No significant differences in morphologically viable (hyaline) cyst production occurred after 24-48 hm when 100 µg CR/mL was used, while the highest concentration of CR (2,000 µg/mL) resulted in a significant decrease of hyaline cyst yield; dead cysts prevailed in cultures, particularly at 72 h of CR treatment. Differentiation of amebas incubated in the presence of 500-2,000 µg/mL CR produced abnormal chitin deposits, rendering irregulary thick or double cell walls, as shown by transmission and scanning electron microscopy. Cyst cultures obtained under 100 µg/mL CR produced as many trophozoites as did the control when they were incubated in BI-S-33, but only low numbers of trophozoites were found in culture cysts obtained under higher CR doses. Conclusion. Our results suggest that CR affects E. invadens encystment, alters the cell wall formation, and also affects the cyst viability

Utrastructural localization of Giardia lamblia antigens by human IgA and IgG

Surface and intracellular antigenic components of Giardia lamblia trophozoites were investigated using anti-giardia IgA and IgG antibodies from human milk and serum. Immunoperoxidase techniques were employed to identify these components with light and electron microscopy. Cryosections of trophozoites of G. lamblia were used with the purpose of allowing direct exposure of intracellular components in the light microscopy studies. Fixed trophozoites of this parasite were used for ultraestructural studies. The antigenic components that were linked with anti-Giardia IgA and IgG antibodies were located diffusely on the full extent of the parasite surface, mainly on the dorsal area. In the frozen section immunostaining was also found in the cytoplasm. Flagella and ventral surface were also immunoperoxidase positive. It is concluded that surface and intracellular antigens of G. lamblia trophozoites induce a human immune humoral response