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OCC MICROBIO 210 PRACTICAL 3 SET EXAM LATEST UPDATED
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OCC MICROBIO 210 PRACTICAL 3 SET EXAM LATEST UPDATED...
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What is a selective medium? - ANSWER growth medium that favors onegroup of microorganisms while inhibiting others
Explain how MSA is selective - ANSWER The NaCl makes it selective
for Staphylococci since most other bacteria are not osmotolerant
What is a differential medium? - ANSWER growth medium that allow
organisms to show visible differences in growth
Explain how MSA is differential - ANSWER different species of staph
show up in variation on the media
MSA favors organisms capable of tolerating__________ - ANSWER
sodium chloride
MSA is used to differentiate pathogenic ___________ species which
ferment mannitol, from less pathogenic species that do not - ANSWER
staphylococcus
the pH indicator in MSA is ________- - ANSWER phenol red
The development of ____________ halos around bacterial growth on
this medium is an indication that mannitol has been fermented with the
production of ___________ - ANSWER yellow, acid end products
Organisms plated on MSA that cant tolerate the level of salinity in the
agar will show what kind of growth? - ANSWER poor or no growth
Describe a negative result on mannitol salt agar (2 possibilities). -
ANSWER 1. poor/no growth: NaCl inhibited; not staph
2. Red/pink growth: Mannitol not fermented; non pathogenic staph
,If bacteria grow on this agar and produce a pink color, is that a positive
or a negative result? What causes the pink color? - ANSWER Negative,
since the organism produces alkaline products
True or false. If an organism grows on mannitol salt agar and produces a
pink color, the organism cannot tolerate the sodium chloride
concentration (osmotic pressure) in the medium. - ANSWER False, it
just doesnt ferment mannitol, but its osmotolerant
Why are selective and differential media like this one very helpful
identifying bacteria? - ANSWER We get to differentiate pathogenic
organisms from others.
Name an organism (genus and species) that gives a positive result on
the agar. - ANSWER Staphylococcus aureus
Your lab manual says that the nutrient agar control plate in this
experiment, is "a comparison for growth quality." Explain why the results
on the nutrient agar plate are necessary to justify your conclusions about
the mannitol salt agar plate.* - ANSWER It is important to show the
differences in growth with and without NaCl
Describe a + result on mannitol salt agar. What did the organism do, in
order to produce this result? - ANSWER Yellow, good growth, which
indicated pathogenic staph. It was not inhibited by NaCl and fermented
mannitol to produce acids
What is hemolysin? - ANSWER a substance that destroys RBCs and
releases hemoglobin
What does alpha hemolysis look like on blood agar? What do bacteria
do to RBC's to produce the typical color of alpha hemolysis? - ANSWER
green zone around colonies which indicates partial destruction of
erythrocytes. The bacteria is streptococcus pneumoniae
What does beta hemolysis look like on blood agar? What are bacteria
doing to RBC's to produce the typical appearance of beta hemolysis? -
, ANSWER clear zones around colonies. the bacteria are destroying the
erythrocytes and hemoglobin.
Which pathogen is an example of a beta hemolytic organism? What
disease does this organism cause? What is the significance of being a
carrier of this organism?* - ANSWER streptococcus agalactiae: can
cause meningitis. pregnant women should be screened for this prior to
giving birth.
Define "normal microbiota" ("normal flora"). - ANSWER microbes living
on or within human host without adverse effects.
Besides the organism mentioned in #20, another beta-hemolytic
pathogen is the nosocomial organism that produces a golden-yellow
pigment and also causes a food borne illness,
__________________________. - ANSWER staphylococcus aureus
What does it mean to say that an organism is "fastidious"? - ANSWER
needs specific growth factors to thrive
Hemolysins produced by bacteria of the genus Streptococcus are called
________________________. - ANSWER streptolysin
What is "presumptive identification" of a microorganism? What organism
are we trying to presumptively identify in the bile esculin test? -
ANSWER it is a screening test to see if there is a possibility of the
bacteria we're looking for in the culture. Enterococcus faecalis.
Esculin is an example of a type of molecule known as a glycoside; its 2
components are the sugar ________________________ and a
compound called ___________________________. - ANSWER
glucose, esculetin
The bile in bile esculin agar inhibits the growth of most
__________________________ bacteria, except
_____________________________ bacteria. - ANSWER gram +, group
d strep and enterococci
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