Question 1

An Entamoeba histolytica trophozoite may be identified by which of the following morphologic features?
A) Ingested RBCs and a single nucleus with a central karyosome
B) Ingested RBCs and a single nucleus with an eccentric karyosome
C) Ingested RBCs, a single nucleus, and a large cytoplasmic glycogen vacuole
D) Ingested WBCs and two nucleoli with central karyosomes

Accepted Answer

Entamoeba histolytica trophozoites have a centrally located karyosome with evenly spaced chromatin in the single nucleus and ingested RBCs.

Question 2

Entamoeba histolytica can be differentiated from E. dispar based on differences in the:
A) Size of the cyst
B) Number of nuclei in the cyst
C) Location of the karyosome
D) None of these. The organisms cannot be differentiated morphologically.

Accepted Answer

E. histolytica and E. dispar cannot be differentiated morphologically unless ingested RBCs are visible in E. histolytica.

Question 3

Entamoeba histolytica can be differentiated from E. hartmanni based on differences in the:
A) Size of the cyst
B) Number of nuclei in the cyst
C) Location of the karyosome
D) None of these. The organisms cannot be differentiated morphologically.

Accepted Answer

E. histolytica and E. hartmanni are differentiated by size: E. histolytica (10 to 20 µm) and E. hartmanni (< 10 µm); E. histolytica also ingests RBCs.

Question 4

The most prominent morphologic feature used to identify Iodamoeba bütschlii is:
A) A large glycogen mass
B) Four nuclei with large karyosomes
C) Ingested bacteria
D) Pointed chromatoidal bars

Accepted Answer

A single large glycogen vacuole is a characteristic finding when attempting to identify I. bütschlii.

Question 5

Drainage from an oral gum lesion revealed the presence of a possible amoeba. An amoeba with a single nucleus and ingested WBCs was noted in a trichrome-stained preparation of the drainage material. Which of the following is the probable parasite found in this sample?
A) Entamoeba histolytica/dispar
B) Entamoeba gingivalis
C) Entamoeba polecki
D) Trichomonas tenax

Accepted Answer

Entamoeba gingivalis is the amoeba most commonly associated with oral infections, particularly in the context of gum lesions. Unlike Entamoeba histolytica/dispar, which primarily affects the colon and can cause dysentery, or Entamoeba polecki, which has a different host specificity and presentation, Entamoeba gingivalis is found in the mouth and is not known to cause systemic disease. Trichomonas tenax, while also found in the oral cavity, is a flagellate and not an amoeba.

Question 6

A permanently stained fecal smear revealed several cysts containing eight nucleoli that had clumped chromatin and eccentrically located karyosomes. The likely identity of this parasite is:
A) Dientamoeba fragilis
B) Endolimax nana
C) Entamoeba coli
D) Entamoeba histolytica

Accepted Answer

The E. coli cyst usually contains five to eight nuclei, whereas E. histolytica's cyst will have up to four nuclei. Other parasitic cysts often have only one or two nuclei, and never more than four.

Question 7

A 10-year-old boy with symptoms of meningitis and a history of swimming in his farm pond was brought to the hospital emergency department. Examination of his CSF revealed motile amoeba measuring 12 µm in diameter. The most likely parasite is:
A) Acanthamoeba spp. trophozoites
B) Dientamoeba fragilis trophozoites
C) Endolimax nana trophozoites
D) Naeglaria fowleri trophozoites

Accepted Answer

N. fowleri lives in warm water ponds and usually enters the host through the mucous membranes of the nose and migrates to the CNS. Acanthamoeba spp. rarely enters the CNS. The other two parasites do not invade the CNS.

Question 8

The parasite most often associated with contaminated contact lens cleaning solution is:
A) Acanthamoeba spp.
B) Dientamoeba fragilis trophozoites
C) Endolimax nana trophozoites
D) Naeglaria fowleri trophozoites

Accepted Answer

Acanthamoeba spp. causes corneal keratitis and comes in contact with eyes through contaminated eye-care solutions. N. fowleri is usually associated with CNS infections.

Question 9

A cyst measuring 25 µm in diameter was observed in a fecal smear. It contained a large, clear central vacuole with four homogeneous nuclei lying outside the vacuole near the cyst wall. This parasitic form suggests the presence of:
A) Blastocystis hominis
B) Endolimax nana
C) Iodamoeba bütschlii
D) Trichomonas tenax

Accepted Answer

B. hominis protozoa are identified using the trichrome stain. The organism is round and varies greatly in size from 6 to 40 ?m in diameter. The central area of the cell resembles a large vacuole surrounded by several small, dark-staining nuclei.

Question 10

The free-living amoeba associated with meningitis is:
A) Dientamoeba fragilis
B) Entamoeba coli
C) Entamoeba histolytica
D) Naegleria fowleri

Accepted Answer

N. fowleri is found in warm pond water. Humans come in contact with this parasite while swimming in the water.

Question 11

Name the parasite shown in the following image: 
A) Entamoeba coli
B) Entamoeba dispar
C) Entamoeba hartmanni
D) Entamoeba histolytica

Accepted Answer

This view is of the amoeba Entamoeba histolytica. The differentiating characteristic is the presence of engulfed RBCs. E. dispar is a nonpathogenic race of E. histolytica and never ingests RBCs. E. hartmanni is a smaller nonpathogenic race of the species. E. coli is differentiated by its distinctly different nuclear structure.

Question 12

Name the parasite shown in the following image: 
A) Dientamoeba fragilis
B) Entamoeba coli
C) Entamoeba hartmanni
D) Iodamoeba bütschlii

Accepted Answer

This view is of the amoeba Dientamoeba fragilis. The differentiating characteristic is the presence of two nuclei in this trophozoite form. All of the other choices have only one nucleus in the trophozoite form.

Quiz 4: Protozoa: Amoeba

An Entamoeba histolytica trophozoite may be identified by which of the following morphologic features?

Entamoeba histolytica can be differentiated from E. dispar based on differences in the:

Entamoeba histolytica can be differentiated from E. hartmanni based on differences in the:

The most prominent morphologic feature used to identify Iodamoeba bütschlii is:

Drainage from an oral gum lesion revealed the presence of a possible amoeba. An amoeba with a single nucleus and ingested WBCs was noted in a trichrome-stained preparation of the drainage material. Which of the following is the probable parasite found in this sample?

A permanently stained fecal smear revealed several cysts containing eight nucleoli that had clumped chromatin and eccentrically located karyosomes. The likely identity of this parasite is:

A 10-year-old boy with symptoms of meningitis and a history of swimming in his farm pond was brought to the hospital emergency department. Examination of his CSF revealed motile amoeba measuring 12 µm in diameter. The most likely parasite is:

The parasite most often associated with contaminated contact lens cleaning solution is:

A cyst measuring 25 µm in diameter was observed in a fecal smear. It contained a large, clear central vacuole with four homogeneous nuclei lying outside the vacuole near the cyst wall. This parasitic form suggests the presence of:

The free-living amoeba associated with meningitis is:

Name the parasite shown in the following image:

Name the parasite shown in the following image: