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 assembly under the effect: of CR dye on encysting E. invadens by means of light and elect ron microscopy, after the amebas were subjected to the effect of 100-2,000 mu g CR/mL. Experiments were performed either in BI-S-33 or in mLG media. Results. Trophozoite growth was not inhibited by 100-1,000 mu g/mL CR after 8 days of incubation in BI-S-33 medium. However, low levels of growth were observed with 2,000 mu g/mL of dye. No significant differences in morpholo gically viable (hyaline) cyst production occurred after 24-48 h, when 100 m u g CR/mL was used, while the highest concentration of CR (2,000 mu g/mL) r esulted in a significant decrease of hyaline cyst yield; dead cysts prevail ed in cultures, particularly at 72 h of CR treatment. Differentiation of am ebas incubated in the presence of 500-2,000 mu g/mL CR produced abnormal ch itin deposits, rendering irregularly thick or double cell walls, as shown b y transmission and scanning electron microscopy. Cyst cultures obtained und er 100 mu g/mL CR produced as many trophozoites as did the control when the y were incubated in BI-S-33, but only low numbers of trophozoites were foun d in culture cysts obtained under higher CR doses. Conclusion. Our results suggest that CR affects E. invadens encystment, alt ers the cell wall formation, and also affects the cyst viability. (C) 1999 IMSS. Published by Elsevier Science Inc.