Acanthamoeba - Classification, Habitat, Morphology, Culture, History

Introduction of Acanthamoeba

Acanthamoeba is a genus of amoebae that are free-living in soil, dust, sand, rivers, ponds, streams, freshwater, and tap water which are aerobic bacterivores. In certain situations, they can cause infections called acanthamebiasis in humans as well as animals.

The pathogenic species of Acanthamoeba which infect humans include Acanthamoeba culbertsoni, Acanthamoeba castellani, Acanthamoeba polyphage, and Acanthamoeba astronyxis. These amoebae infect:

• human central nervous system (CNS) to cause opportunistic granulomatous infections

• in healthy individuals, eyes may be infected

• in immunocompromised patients, lungs and skin might be infected

Classification of Acanthamoeba

Domain: Eukaryota

Phylum: Amoebozoa

Class: Discosea

Order: Centramoebida

Family: Acanthamoebidae

Genus: Acanthamoeba

History of Acanthamoeba

Culbertson and his team were the first to prove the pathogenicity of Acanthamoeba by infecting lab mice through intra-nasal inoculation which resulted in the production of purulent meningoencephalitis.

Habitat of Acanthamoeba

In humans, Acanthamoeba species inhabit the mouth and the pharynx as commensals. They are also found in the soil, dust, sand, rivers, ponds, streams, freshwater, and tap water.

Morphology of Acanthamoeba

Acanthamoeba species occur in two morphological stages:

Trophozoite

• Acanthamoeba trophozoites are large in size: 10-40μm in diameter

• variable in shape and size

• finely granular cytoplasm contains a single nucleus, mitochondria

• the nucleus contains a prominent nucleolus which is large, dense, and surrounded by a halo

• the presence of acanthopodia confirms Acanthamoeba trophozoites

  acanthopodia are distinctive, slender, spine-like projections of the plasma membrane

Cyst

• Acanthamoeba cysts measure 15-20 μm in diameter

• are variable in size and might be polygonal, spherical, or star-shaped

• have a double layered cyst-wall

  endocyst (inner wall) is smooth but the shape may be triangular, oval, round, or polygonal and has pores or opercula in numerous points

  exocyst (outer wall) is mostly rippled or wrinkled

• contains a nucleus located at the center with a clear halo and large dense karyosomes

Culture of Acanthamoeba

In media, Acanthamoeba can be grown:

• Non-nutrient agar inoculated with monoxenic culture of bacteria such as Enterobacter species and Escherichia coli

• Axenic culture – enriched broth without added bacteria

• monolayer cell lines cultures such as Hela cells, MRChuan embryonic lung cells, and monkey kidney cells

• grows best at 25° C - 30° C

• can encyst both in vitro and in vivo and excysts back to trophozoites when cultured