LAB REPORT 2- Selected
questions from Exercise 3-7 (Acid-fast stain)
Note: This is turned in
after you have viewed your acid fast stain slides.
Bacteria for this exercise
are: Mycobacterium smegmatis (or M. phlei) and S. aureus.
Q1.
Acid fast bacteria have some significant differences as compared to non-acid fast
bacteria. What is the major chemical (structural) difference among these
acid fast bacteria that might explain why the need for the acid-fast stain
procedure? Hint: This structural difference also affects the way the bacteria
grow on media (both broth and media containing agar) and the length of time
they take to grow.
Q2.
(Use the lab manual to answer this) How does heating the bacterial smear during
a Ziehl-Neelson stain procedure promote entry of carbol fuchsin into the acid
fast cell wall? Why is the Kinyoun procedure referred to as the cold acid
fast stain procedure? Explain what happens instead in the Kinyoun stain
procedure during the application of the carbol fuchsin.
Q3.
Are acid fast negative bacteria stained by carbol fuchsin? If so, explain why
the acid fast stain is considered to be a differential stain?
Note:
Why do you suppose the acid fast stain in not as widely used as the Gram
stain? When is it more useful than the
Gram stain? Can you name the bacterial
genera that are considered to be acid fast?
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