Auxotrophy to lipoproteins of Entamoeba histolytica cultivated under axenic conditions

Abstract

Entamoeba histolytica grows in media without serum but with a mixture of aminoacids, vitamins, lipoproteins, free cholesterol, phospholipids and fatty acids called PACSR. The ability of lipoproteins and free lipids to support growth of three E. histolytica strains (HK9, HMI:IMSS and HM3:IMSS) was analysed. Tubes containing 5 ml culture medium, amino acids, vitamins and either 120–1,200 μg lipoproteins/ml or 0.017–0.10 mg free lipids/ml (predissolved in absolute ethanol) were inoculated with 1 × 10⁴ trophozoites/ml and incubated at 37 °C for 72 h. Amoebae died within 12 h in the presence of any free lipid combination, while those having 240–480 mg lipoproteins/ml reached densities similar to or higher than those of controls (depending on strain). The addition of ethanol (0.1%) to the media produced stable lipid solutions and did not show significant adverse effects. Accordingly, E. histolytica is auxotrophic to lipoproteins and unable to use free cholesterol, phospholipids or fatty acids.