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Protozoal Microorganisms as Intestinal Parasites 57

However, it is important to distinguish this organism defin- features and structures. A permanent stained smear is
itively from those parasites that are pathogenic. E. coli may the best means for identifying this organism.
occur simultaneously with another intestinal protozoan.
Treatment and Prevention
Life Cycle
The nonpathogenic E. coli do not require any treatment
E. coli enjoys a similar life cycle as the other amoebae unless concomitant infection with other organisms occurs.
where simple reproduction is accomplished by binary Ensuring cleanliness of food and water that has been
longitudinal fission. However, there is no extra-intestinal purified is necessary to prevent infection. Flies and cock-
stage such as that found with E. histolytica where inva- roaches should be prevented from gaining access to foods.
sion of other tissues occurs.

OTHER IMPORTANT AMOEBAL
Disease Transmission
ORGANISMS IN INTESTINAL
Patients with E. coli infections are generally, but not PARASITOSIS
always, asymptomatic. As is the case with many other
parasites, transmission is chiefly by ingesting the or- Although E. histolytica is the most important amoeba that
ganism with food and water that are contaminated with is responsible for producing disease of the gastrointesti-
amoebic cysts. Cockroaches have also been implicated in nal tract of humans, there are other species that are patho-
transmitting the disease to humans where these insects genic. An added problem is the ferreting out of organisms
have contaminated food products. that are not pathogenic, and differentiating between them
and the important disease-causing parasites. A system-
Laboratory Diagnosis atic approach of comparing morphology is helpful in dif-
ferentiating between the large variety of organisms that
Diagnosis of the presence of an E. coli infection relies might be encountered in stool specimens, and can be a
on the standard examination of a fresh fecal specimen challenge even to experienced medical professionals. The
for ova and parasites for characteristic morphological use of table such as Table 3-4 and comparative charts are

TABLE 3-4 Comparison of E. histolytica with Common Nonpathogenic Amoebae

E. HISTOLYTICA E. COLI E. HARTMANNI E. DISPAR
Trophozoites Trophozoites Trophozoites Trophozoites

20–40 μm 20–25 μm 8–10 μm 15–20 μm
Motility increased when Sluggish and Less progressive motility Progressive movement
warm nondirectional movement than E. dispar
Extended pseudopodia Broad, blunt pseudopodia
Extended pseudopodia
Cysts Cysts Cysts Cysts
8–20 μm 20–25 μm 6–8 μm 12–15 μm
1 to 4 nuclei (4 in mature 8 nuclei 4 nuclei 4 nuclei
form)
Squat, oval chromatoid Pointed chromatoid Blunt chromatoid bodies Blunt chromatoid bodies
bodies bodies