Amoebae

Lab:2 Practical Microbiology (Parasitology)
The parasites are classified as three phyla into
1. phylum: protozoa
2. phylum: platyhelminthus
3. phylum: nematoda
Classes of Protozoa:
Type of locomotion of organelle has been used to divide these into four major classes:
1. Rhizopods (amoebae): Entamoeba histolytica& Entamoeba coli
2. Ciliaphora : Blantidium coli
3. Mastigophora or flagellated: Giardia lamblia, Trichomonas vaginalis, Leishmania & Trypanosoma
4. Sporozoa: Plasmodium, Toxoplasma gondii

1. Class: Rhizopods (amoebae): Entamoeba histolytica& Entamoeba coli
Entamoeba histolytica

Trophozoites

The trophophozoite exhibits rapid, unidirectional, progressive movement, achieved with the help of finger like hyaline pseudopods. The single nucleus typically contains a small and central Karyosome. Variants of the karyosome include eccentric or fragmented karyosomal material. The peripheral chromatin is typically fine and evenly distributed around the nucleus in a perfect circle. The E. histolytica trophozoite finely granular cytoplasms, Red blood cells in the cytoplasm are considered diagnostic because E. histolytica is the only intestinal ameba to exhibit this characteristic. Bacteria, yeast, and other debris may also reside in the cytoplasm, but their presence, however, is not diagnostic.






Cyst

The spherical to round cysts of E. histolytica are typically smaller than the trophs, measuring. The presence of a hyaline cyst wall helps in the recognition of this morphologic form. Young cysts characteristically contain unorganized chromatin material that transforms into squared or round – ended chromatoid bars in order cysts. The chromatoid bars may or may not be present in mature cysts. A diffuse glycogen mass is also usually visible in young cysts. As the cyst matures, the glycogen mass usually disappears. One to four nuclei are usually present. The mature infective cyst is quadri nucleated (containing four nuclei). The cytoplasm remains fine and granular. Red blood cells, bacteria, yeast, and other debris are not found in the cyst stage.











Life cycle

Once the infective stage is ingested, excystation occurs in the small intestine. As a result of the nuclear division, a single cyst produces eight motile trophozoites. These motile amebae settle in the lumen of the large intestine, where they replicate by binary fission and feed on living host cells. On occasion, trophzoites migrate to other organs in the body, such as the liver, and may cause abscess formation. Encystation occurs in the intestinal lumen, and cyst formation is complete when four nuclei are present. These infective cysts are passed out into the environment in human feces and are resistant to a variety of physical conditions. Survival in a feces contaminated environment for up to a month is common.

Clinical symptoms

Amebiasis, an infection of the intestine or liver by an ameba, often Entamoeba histolytica. The amebae are present in food or water that has had contact with infected feces. Amebic dysentery, intestinal amebiasis. An inflammation of the intestine caused by Entamoeba histolytica. Symptoms are frequent, loose stools flecked with blood and mucus. An amebic abscess often accompanies amebic dysentery.

Laboratory diagnosis

Stool examination is the method of choice for recovery of E. histolytica trophozoites and cysts. Through using wet preparations and permanent staining techniques on a suspected stool. When E. histolytica is suspected but not recovered in stool samples. Other laboratory tests including serological procedures may be utilized such methods currently available include Enzyme –Linked Immunosorbent Assay (ELISA).



Entamoeba coli

Trophozoite

The trophozoite is equipped with blunt pseudopods and exhibits sluggish, nonprogressive motility. The single nucleus is easily recognizable. In unstained preparations, the karyosome and the peripheral chromatin appear as refractile structures . The nuclear structures are enhanced when the trophozoites are stained . The typical nucleus consists of a large , often irregularly shaped karyosome that is eccentrically located . The karyosome is surrounded by unevenly distributed peripheral chromatin that varies in size and becomes apparent with addition of stain. Vacuoles, often containing bacteria , are commonly seen in the coarsely granulated cytoplasm . In contrast to E. histolytica, red blood cell inclusions do not occur .


Fig. ( 3 ) : Entamoeba coli trophozoite
Cysts

A thick cell wall surrounded the round to spherical cyst . As with the trophozoite , the cyst nuclei are readily discernible . One to eight nuclei with the typical nuclear features may be seen in unstained as well as stained preparations.Occasionally , large cysts containing 16 or more nuclei may be present . The granular cytoplasm may contain thin chromatoid bars , often with pointed to splintered ends. The glycogen mass may displace the nuclei present to opposite ends of the cyst.












Life cycle

Life cycle of E. coli is similar to E. histolytica life cycle with the exception of difference in cyst nucleus numbers.

Clinical symptoms
Infections with E. coli are usually asymptomatic.

Laboratory diagnosis

General stool examination is the method of choice for recovery of E. coli trophozoites and cysts. The presence of E.coli suggests ingestion of contaminated food or drink. The technologist should therefore examine such preparations carefully for the presence of pathogenic parasites in addition to the nonpathogenic E. coli.





Table showing the comparison between trophozoite of E. histolytica& E. coli
characteristic
Troph. of E. histolytica
Troph. of E. coli
No. of nuclei One one
Karyosome Small& centeral Large irregular shape, eccentric
Peripheral chromatin Fine& evenly distributed Coarse& unevenly distributed
Cytoplasm Finely granular Coarse& often vacuolated
Cytoplasmic inclusion Ingested RBC Bacteria, other debris
Motility Progressive, finger like pseudopodia Non Progressive, blunt pseudopodia


Table showing the comparison between cysts of E. histolytica& E. coli
Characteristic cyst of E. histolytica
cyst of E. coli
Shape Spherical to round Spherical to round
No. of nuclei One to four One to eight
Karyosome Small& centeral Large irregular shape, eccentric
Peripheral chromatin Fine& evenly distributed Coarse
Cytoplasm Finely granular granular
Cytoplasmic inclusion Chromatoid bars, rounded ends, diffuse glycogen mass Chromatoid bars, rounded with pointed ends, diffuse glycogen mass