Congo Red Effect on Cyst Viability and Cell Wall Structure of Encysting Entamoeba invadens

Abstract

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 assembly under the effect of CR dye on encysting E. invadens by means of light and electron microscopy, after the amebas 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 Trophozoite 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 h, 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 irregularly 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.