Sarcodina (Amoeba) Lecture Review

Vocabulary flashcards covering taxonomy, morphology, life cycle, clinical features, diagnosis, treatment and key species of amoebae discussed in the lecture.

Sarcodina

Sub-phylum of protists that move and feed by extending pseudopodia; includes amoebae.

Amoeba

Unicellular protist that locomotes with pseudopods; many species are free-living, some are parasitic.

Pseudopod

Temporary cytoplasmic projection used by amoebae for movement and engulfing food.

Trophozoite

Motile, actively feeding and multiplying stage of an amoeba; vulnerable outside the host.

Cyst

Non-motile, dormant, environmentally resistant stage; infective form for most amoebae.

Pre-cyst

Rounded trophozoite that precedes cyst formation but lacks a protective cyst wall.

Encystation

Process by which a trophozoite rounds up, secretes a cyst wall and becomes a cyst.

Excystation

Emergence of a trophozoite from the cyst after exposure to favorable conditions.

Chromatoid body

Rod-shaped RNA-protein aggregate in Entamoeba cysts; cigar-shaped with rounded ends.

Glycogen vacuole

Starch reserve in amoeba cysts that stains deeply with iodine.

Karyosome

Central or eccentrically placed clump of nuclear chromatin useful for amoeba identification.

Peripheral nuclear chromatin

Fine granules lining the inner nuclear membrane of amoebae.

Ectoplasm

Clear outer layer of cytoplasm in amoebae, involved in pseudopod formation.

Endoplasm

Granular inner cytoplasm of amoebae, often containing food vacuoles or ingested RBCs.

Entamoeba histolytica

Pathogenic intestinal amoeba that causes amebic dysentery and liver abscesses.

Amebic dysentery

Severe bloody diarrhea due to invasion and ulceration of colonic mucosa by E. histolytica.

Amebic liver abscess

Extra-intestinal collection of necrotic “chocolate-colored” pus in the liver caused by E. histolytica.

Non-invasive amebiasis

Colonization of colon lumen by E. histolytica without tissue invasion; often asymptomatic cyst passage.

Invasive amebiasis

Form in which E. histolytica penetrates mucosa, causes ulcers, dysentery, and may disseminate to liver or other organs.

Ameboma

Granulomatous mass in colon formed by chronic invasive E. histolytica infection.

Sarcomastigophora

Phylum that contains flagellates and amoebae, including sub-phylum Sarcodina.

Lobosea

Class of amoebae with blunt, lobed pseudopodia; includes order Amoebida.

Entamoeba coli

Non-pathogenic intestinal amoeba distinguished by larger cysts with up to 8 nuclei.

Endolimax nana

Small, non-pathogenic intestinal amoeba; cysts have 1–4 large blot-like karyosomes.

Iodamoeba bütschlii

Non-pathogenic intestinal amoeba whose cyst contains a large iodine-positive glycogen vacuole.

Naegleria fowleri

Free-living ‘brain-eating’ amoeba causing primary amoebic meningoencephalitis (PAM).

Primary amoebic meningoencephalitis (PAM)

Acute, often fatal CNS infection by N. fowleri acquired through nasal exposure to warm fresh water.

Acanthamoeba spp.

Free-living amoebae with spiny pseudopods (acanthopodia); cause keratitis and granulomatous amoebic encephalitis.

Granulomatous amoebic encephalitis (GAE)

Chronic CNS disease in immunocompromised hosts caused by Acanthamoeba or Balamuthia.

Acanthopodia

Filamentous, spine-like pseudopods characteristic of Acanthamoeba trophozoites.

Flagellated form (Naegleria)

Transient, pear-shaped stage with two flagella; occurs in environment and CSF but not in Acanthamoeba.

Human reservoir of E. histolytica

Only humans harbor and shed infectious cysts, excreting up to 45 million cysts per day.

Infective stage of E. histolytica

Mature tetranucleated cyst ingested via contaminated food, water, or hands.

Stool microscopy

Laboratory method to detect E. histolytica cysts or trophozoites in fecal samples.

Metronidazole

Drug of choice for invasive E. histolytica infections; also used with tinidazole.

Risk factors for amebiasis

Poor sanitation, contaminated water, crowding, low socioeconomic status, male homosexuality, malnutrition.

Contractile vacuole

Organelle that collects and expels excess water from amoebae, maintaining osmotic balance.

Food vacuole

Membrane-bound vesicle containing engulfed food particles inside amoebae.

Facultative parasite

Organism usually free-living that can become parasitic under certain conditions, e.g., Acanthamoeba.

Thermotolerance of E. histolytica cyst

Cysts survive temperatures up to 55 °C and normal chlorination levels.

Trogocytosis

Process by which N. fowleri nibbles and ingests live host cell membranes, leading to cell death.

Membrane Attack Complex (MAC)

Terminal complement complex that lyses pathogens; N. fowleri evades it by shedding bound MAC.

Amphotericin B

Antifungal/antiparasitic agent administered intravenously and intrathecally to treat PAM.

Amebic keratitis

Vision-threatening corneal infection by Acanthamoeba, often linked to contaminated contact lenses.

Sulfamethazine

Sulfonamide drug used in combination therapy for Acanthamoeba infections.