Please see the following review paper for information and references:

http://cmr.asm.org/content/15/3/329.full.pdf+html

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histolytica was first introduced by Boeck and Drbohlav in 1925

in a diphasic egg slant medium, and a modification of this

medium (Locke-egg) is still used today (35). Different

monophasic media that were developed for E. histolytica are

the egg yolk infusion medium of Balamuth (12), Jones’s medium

(96), and TYSGM-9 (41). Of the different media developed

for the xenic cultivation of E. histolytica, only three media,

diphasic Locke-egg, Robinson’s medium (150), and the

monophasic TYSGM-9 (41), are in common use (for details,

see reference 35).

Axenic cultivation involves the cultivation of parasites in the

absence of any other metabolizing cells (35). The axenic cultivation

of E. histolytica was first achieved by Diamond in 1961

(39). The monophasic medium TP-S-1 was developed and used

widely for culture of E. histolytica in different research laboratories

(35, 40). Currently TYI-S-33 (45) and YI-S (44) are the

most widely used media for axenic cultivation of E. histolytica

(35).

Culture of E. histolytica can be performed from fecal specimens,

rectal biopsy specimens, or liver abscess aspirates. As

the liver abscess aspirates of ALA patients are usually sterile

(98% cases) (19), addition of a bacterium or a trypanosomatid

is necessary before inoculation of amebae into xenic culture

(35, 53, 204).

The success rate for culture of E. histolytica is between 50

and 70% in reference laboratories (35). As culture of E. histolytica

from clinical samples such as feces or liver abscesses

has a significant false-negative rate and is technically difficult,

it is not undertaken in a routine clinical laboratory.

Entamoeba dispar can be grown in xenic culture; however,

most isolates grow poorly in monoxenic culture, and the

growth of only a few strains has been reported to be viable in

TABLE 1. Characteristics of trophozoites and cysts of common intestinal Entamoeba speciesa

Characteristics E. histolytica/E. dispar/

E. moshkovskii E. hartmanni E. coli E. polecki

Size, nuclei, and motility

Trophozoites 15–20 m, 1 nucleus (difficult

to see in unstained

preparations), actively

motile with finger shaped

pseudopodia

8–10 m, 1 nucleus (usually

not seen in unstained

prepn), usually

unprogressive

20–25 m, 1 nucleus (often

visible in unstained prepn);

sluggish, short, and blunt

pseudopodia

15–20 m, 1 nucleus

(occasionally seen on wet

prepn), sluggish

Cysts 10–15 m, mature cyst with 4

nuclei, immature cyst has 1

or 2 nuclei (nuclear

characters difficult to see

on wet prepn)

6–8 m, mature cyst with 4

nuclei, immature cyst has 1

or 2 nuclei, two nucleated

cysts very common

15–25 m, mature cyst has 8

nuclei, occasionally 16 or

more nuclei

10–15 m, mature cyst with

1 nucleus, rarely 2 or 4

nuclei

Other features

Trophozoites

Chromatin (stained) Chromatin peripheral, may

have beaded appearance

Nucleus may stain more darkly

than E. histolytica, chromatin

may appear as solid ring

rather than beaded

(trichrome)

Chromatin clumped and

unevenly arranged, appears

as solid ring with no beads

Chromatin finely granular,

chromatin may also be

clumped at one or both

edges of membrane

Karyosome

(stained)

Karyosome small, compact,

centrally located but may

be eccentric

Karyosome usually small and

compact; centrally located or

eccentric

Karyosome large, not compact,

may or may not be eccentric,

may be diffuse or darkly

stained

Karyosome small and

usually centrally located

Cytoplasm (stained) Cytoplasm is fine, granular,

may contain bacteria;

presence of RBCs

diagnostic for E. histolytica,

although some E. dispar

strains may very

occasionally contain RBCs

Cytoplasm finely granular, may

contain bacteria, no RBCs

Cytoplasm granular with

differentiation into

cytoplasm and endoplasm,

vacuolated; bacteria, yeast,

and other debris may be

present

Cytoplasm is finely granular,

may contain ingested

bacteria

Cysts

Chromatin (stained) Chromatin peripheral with

fine uniform granules,

evenly distributed

Chromatin granules evenly

distributed (nuclear

characteristics may be

difficult to see)

Chromatin coarsely granular,

may be clumped and

unevenly arranged

Chromatin finely granular

Karyosome

(stained)

Karyosome is small, compact,

usually centrally located

but occasionally eccentric

Karyosome is small, compact,

usually centrally located

Karyosome large, eccentric,

occasionally centrally located

Karyosome small and

usually centrally located

Cytoplasm (stained) May be present;

chromatoidal bodies

usually elongate with blunt,

rounded, smooth edges;

may be round or oval;

chromatin may be diffuse

or absent in mature cyst;

clumped chromatin mass

may be present in early

cysts

Usually present; chromatoidal

bodies usually elongate with

blunt, rounded, smooth

edges; may be round or

oval; chromatin may or may

not be present

May be present (less frequent

than in E. histolytica),

splinter shaped with rough

pointed ends, may be diffuse

or absent in mature cysts,

clumped mass occasionally

seen in mature cysts

Abundant chromatoidal

bodies with angular

pointed ends, thread-like

chromatoidal bodies may

also be present, half of

the cysts contain spherical

or ovoidal inclusion mass

a Data are from references 57, 73, and 188.

VOL. 20, 2007 LABORATORY DIAGNOSTIC TECHNIQUES FOR ENTAMOEBA SPECIES 515

axenic culture, suggesting that E. dispar may be less able than

E. histolytica to obtain nutrients in a particle-free medium (29,

103). The use of different media for the culture of E. dispar has

been investigated, and these studies indicate that YI-S may not

be a suitable medium for the culture of E. dispar (35, 103).

For E. moshkovskii strains, culture media employed include

TTY-SB-monophasic with the trypanosomatid, TP-S-1-GM

monophasic for the axenic culture of amebae (40), and the

TP-S-1-GM monophasic medium (42). Other media containing

bovine serum used for culture of E. moshkovskii include

axenic medium TYI-S-33 with 10% bovine serum at 24°C (45)

or xenic medium TYSGM-9 with 5% bovine serum at either

24°C or 37°C (41).

Culture of E. histolytica in a clinical diagnostic laboratory is

not feasible as a routine procedure and is less sensitive than

microscopy as a detection method (35). Parasite cultures are

difficult, expensive, and labor-intensive to maintain in the diagnostic

laboratory (35). Overgrowth of bacteria, fungi, or

other protozoans during culture is the main problem encountered,

and therefore culture is not recommended as a routine

diagnostic procedure for the detection of Entamoeba species