Exercise 10
Questions
1. Discuss the relative convenience of pour- and streak-plate techniques in
culturing clinical specimens?
2. Why are plate cultures incubated in the inverted positions?
3. How do you decide which colonies should be picked from a plate culture
of a mixed flora?
4. Why is it necessary to make pure subcultures of organisms grown from
clinical specimens?
5. How can you determine whether a culture or subculture is pure?
6. What kinds of clinical specimens may yield a mixed flora in bacterial
cultures?
Page 3 of 5
From Laboratory Manual & Workbook in Microbiology Applications to Patient Care (9th ed.). By
Josephine A. Morello, Helen Eckel Mizer, and Paul A. Granato Copyright © 2006 The McGraw-
Hill Companies, Inc. Reprinted with permission of The McGraw-Hill Companies, Inc.
BIO2071_Microbiology Laboratory
7. When more than one colony type appears in pure culture, what are the
most likely sources of extraneous contamination?
Exercise 16
Questions
1. Define a differential medium and discuss its purpose.
2. Define a selective medium and describe its uses.
3. Why is MacConkey agar selective as well as differential?
4. Why is blood agar useful as a primary isolation medium?
5. How can one distinguish E. coli from P. aerugionosa on
Nutrient agar?
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Blood agar?
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MAC agar?
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6. What is the major difference between Modified Thayer-Martin (MTM) and
chocolate agar? When would you use MTM rather than chocolate agar?
7. If you wanted to isolate S. aureus from a pus specimen containing a mixed
flora, what medium would you choose to get results most rapidly? Why?
8. What is the value of making a Gram stain directly from a clinical
specimen?
9. Why is aseptic technique important in the laboratory? In patient care?
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