Amoebozoa, amebae, and slime molds

Amebae are naked protistan cells that have an absorptive nutrition and within the Amoebozoa are the slime molds, the lobose amebae, testate amebae, and some pathogenic species. They have a wide distribution, living free in soil and water, and as parasites of animals and man.

Often grouped together, Dictyostelids and the Myxogastrids are phyla that contain the slime molds. The Dictyostelids, cellular slime molds, exist for most of their life cycle as haploid amebae that feed within soil by engulfing bacteria. They are uninucleate for most of their life cycle but form a plasmodium at sporulation. Myxogastrids are acellular slime molds. They exist as haploid amebae for their vegetative stage, but fuse in pairs to form a diploid cell that undergoes repeated mitotic nuclear divisions without cell division, forming a plasmodium. The life cycle is then very similar to the cellular slime molds.

Pathogenic amebae include Entamoeba, Acanthamoeba, and Naegleria. These pathogens have a number of different organ specificities. Entamoeba causes lesions in the gut causing mucosal destruction with abdominal pain, bloody diarrhea, and vomiting. Acan­ thamoeba infects the cornea, causing blinding keratitis, usually associated with contact lens use, but in immunocompromised patients it can also cause granulomatous enceph- alitis involving the central nervous system. Naegleri amebae enter the nasal passage (during swimming/diving into the water) and migrate along the olfactory nerves, through the cribriform plate into the brain. Infection is almost always fatal.