Down regulation of Entamoeba histolytica virulence by monoxenic cultivation with Escherichia coli O55 is related to a decrease in expression of the light (35-kilodalton) subunit of the Gal/GalNAc lectin

Entamoeba histolytica virulence is related to a number of amebic components (lectins, cysteine proteinases, and amebapore) and host factors, such as i ntestinal bacterial flora. Trophozoites are selective In their interactions with bacteria, and the parasite recognition of glycoconjugates plays an im portant role in amebic virulence. Long term monoxenic cultivation of pathog enic E, histolytica trophozoites, strains HK-9 or HM-1:IMSS, with Escherich ia coli serotype O55, which binds strongly to the Gal/GalNAc amebic lectin, markedly reduced the trophozoites' adherence and cytopathic activity on ce ll monolayers of baby hamster kidney (BE-IK) cells. Specific probes prepare d from E, histolytica lectin genes as well as antibodies directed against t he light (35-kDa) and heavy (170-kDa) subunits of the Gal/GalNAc lectin rev ealed a decrease in the transcription and expression of the light subunit i n trophozoites grown monoxenically with E. coli O55, This effect was not ob served when E, histolytica was grown with E, coli 346, a mannose-binding ty pe I pilated bacteria. Our results suggest that the light subunit of the am ebic lectin is involved in the modulation of parasite adherence and cytopat hic activity.