Comparison between R-phycocyanin-labeled and R-phycoerythrin-labeled monoclonal antibody (Mab) probes for the detection of Entamoeba histolytica trophozoites.

A comparison between R-phycocyanin (R-PC)-labeled monoclonal antibody (MAb) probe and R-phycoerythrin (R-PE)-labeled MAb probe for the detection of the three standard reference strains of the cultured-derived Entamoeba histolytica trophozoites, namely HK-9, HM-1:IMSS, and HTH-56:MUTM were evaluated by using direct immunofluorescence antibody (DIFA) assay five times for each strain. Under the blue irradiation of the fluorescent microscope, both R-PC-labeled and R-PE-labeled MAb probes showed consistently greenish-yellow trophozoites and golden-orange trophozoites, respectively. The R-PE-labeled MAb probe stained the trophozoites more brightly and clearly than those stained by the R-PC-labeled MAb probe of the same Eh208C2-2MAb. When observed under the green irradiation, both probes showed the same intensity of brightly red color at the trophozoites of all three strains of E. histolytica. The sensitivity of both tests was 100%. Since this Eh208C2-2MAb could recognize specifically E. histolytica pyruvate:ferredoxin oxidoreductase (PFOR) enzyme, therefore, our two antibody probes would be valuable for use as a rapid, easy and sensitive test for diagnosis of invasive amebiasis. Further applications of these two probes directly onto the fecal sample spots and to more culture-derived strains of E. histolytica/E. dispar of known zymodemes in collaboration with the International Centre for Diarrhoeal Disease Research, Bangladesh (ICDDRB), Dhaka, Bangladesh, are under investigation.

Application of local products R-phycoerythrin and monoclonal antibody as a fluorescent antibody probe to detect Entamoeba histolytica trophozoites.

R-phycoerythrin (R-PE) was extracted from red algae, Gracilaria fisheri from Pattani Province, Thailand, with 50 mM sodium phosphate buffer, pH 7.0, followed by precipitation with 30-50% final concentration of saturated ammonium sulphate solution at 0 degree C. The precipitate was further purified by DEAE-cellulose (DE-52) column chromatography. The purified R-PE showed a single band of Mr 240 kDa by polyacrylamide gel electrophoresis with the maximum absorption and maximum fluorescence emission at 565 nm and at 573 nm respectively, and the OD ratio of 565 to 280 nm was 6.7. The IgG fraction of a murine monoclonal antibody (Eh208C2-2 MIgG) raised against trophozoites of HM-1: IMSS strain of pathogenic E. histolytica was conjugated with purified R-PE by using the heterobifunctional compound N-succinimidyl3-(2-pyridyldithio)propionate (SPDP). The conjugate was shown by direct immunofluorescent antibody (DIFA) assay to stain specifically both the culture-derived and stool-derived E. histolytica trophozoites.