Chapter 5
Eukaryotic Cells and Microorganisms
I.
Introduction
An outbreak of a diarrheal infection occurred amongst a group of children in Ohio. The
local department of health conducted an investigation and found that the outbreak
appeared to be linked to a local swimming pool. Investigation found that the causative
agent of the outbreak was a protozoan, Cryptosporidium parvum. Oocysts are resistant to
chemical disinfection (such as chlorination in a swimming pool) and only 1–10 oocysts
are needed to cause infection.
II.
Facts of the Case
Initial analysis of the case should result in the following points being agreed upon by the
class:
 Several children were hospitalized with various gastrointestinal problems.
 Within one month, over 150 people in the same geographic region appeared to
experience similar symptoms.
 The local health department reported that the outbreak was linked to a swimming
pool at a private club, which was closed by the health department in late July.
 A total of over 700 individuals eventually showed clinical signs of this diarrheal
disease during the outbreak.
 The outbreak period was from June through September.
Student questions:
Compare and contrast initial steps in the cultivation and identification of protozoa
versus bacteria.
Cryptosporidium are classified as Apicomplexan protozoa. What criteria are used to
classify protozoa?
In this case, what might exclude most bacteria from being the cause of the diarrheal
disease whose source was the swimming pool?
List the five I's of bacterial cultivation and characterization . How many of these are
used to identify Cryptosporidium?”
Compare and contrast bacterial endospores and oocysts formed by some
protozoans.
Cryptosporidium have been isolated from contaminated oysters. Oysters have been
implicated in many diarrheal outbreaks caused by a variety of microorganisms.
Name two different organisms that might be found in contaminated oysters. Why do
you think oysters are often involved in such outbreaks?
Cryptosporidium parvum has a very “low infectious dose.” Another microorganism
that causes diarrhea and also has a low infectious dose is the bacterium, Shigella.
What ability would both of these organisms have in common?