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G+ Lab practical
Terms in this set (65)
Are staphylococci gram positive or gram negative?
What are two examples of Staph?
S. aureus and S. epidermidis
Are streptococci gram-positive or gram-negative?
What are some examples of Strep?
Enterococcus faecalis - used to be called S. faecalis but name changed, still considered part of the Streptococci
What does PEA stand for
Phenylethyl Alcohol Agar
PEA is what type of media?
What is PEA selective for? and against?
For: G(+) Bacteria
Against: G(-) Bacteria
What will grow on PEA plate?
G + will grow
G - will be inhibited
some G- bacteria are not completely inhibited by this agar.
PEA interferes with what cellular process in G- organisms?
PEA can be used to limit the growth of ___________________ species when you try to isolate the _________________ species in a mixed sample
Test that determines whether or not bacteria has "catalase" enzyme.
Catalase test is used to differentiate what 2 groups of bacteria?
Staphylococcus and Streptococcus
What is the chemical reaction involving catalase?
What is observed if the bacteria are catalase positive?
What gas produces the bubbles?
Results for Catalase test
Was S. pyogenes catalase positive or negative
Was S. aureus catalase positive or negative
S. Pyogenes is negative for catalase production
S. aureus is positive for catalase production
Is H2O2 generally more toxic to staphs or streps?
Because Staphylococcus can break down toxic H2O2, can H2O2 still be effective in killing it?
Killing of S. aureus w/ H2O2 involves the formation of the more toxic hydroxyl radical through the iron dependent fenton reaction. Iron reacts with some of the hydrogen peroxide to form free radicals
How do free radicals kill bacteria
1. they can react with plasma membrane lipids, altering membrane permeability
2. they can react with DNA
Which Staphylococcus aureus strains are more protected from the toxic effects of H2O2? Pigmented or nonpigmented?
What does BAP stand for?
blood agar plate
Is the BAP medium selective or differential?
The BAP medium is differential,
The medium differentiates on the basis of red blood cell hemolysis
What are the 3 patterns of hemolysis that can occur on blood agar and how do they appear?
Beta Hemolysis - Complete hemolysis; clearing around colonies
Alpha Hemolysis - incomplete hemolysis; green halos around isolated colonies
Gama Hemolysis - no hemolysis; the agar is unchanged.
What exoenzyme produced by the bacteria results in beta hemolysis?
Hemolysis is significant for what group/genus of G(+) bacteria?
Specifically, what causes the green color seen around colonies exhibiting alpha hemolysis?
What type of hemolysis will be exhibited by alpha hemolytic species if oxygen is removed
What is the purpose of stabbing the agar with the inoculating loop?
the hemolysis produced by streptococci perform better in a microaerophilic environment. Stabbing provides an area of lower oxygen concentration.
S. pyogenes - Beta Hemolysis
S. sanguinis - Alpha Hemolysis
E. faecalis - Gamma Hemolysis
What does MSA stand for?
Mannitol Salt Agar
Is MSA selective or differential or both?
MSA is selective based on
If bacteria grow well on this type of medium, they are salt
MSA is differential based on
what is produced from the fermentation of sugars?
What is the pH indicator in MSA
phenol red turns _________ when pH is ___________
What kind of organic molecule is mannitol
What color indicates a positive mannitol fermentation result?
what color indicates a negative mannitol fermentation result
Mannitol fermentation: positive
Mannitol fermentation: negative
mannitol fermentation: positive
stayphylococcus aureus and Staphylococcus epidermidis are part of the normal flora of
Enterococcus faecalis is part of the normal flora of the
Staphylococci are salt _______________ and Streptococci are salt __________________
Which Strep is an exception to the salt tolerant generalization
is the coagulase test selective or differential?
Coagulase test used to differentiate Staphylococcus _______________ and Staphylococcus ________________
What is observed with a positive coagulase test?
serum clots = jello blob
Identify 2 ways coagulase production correlates with pathogenicity
1. bacteria can multiply inside a blood clot w/o being detected, when they dissolve the clot they are too numerous for the immune system
2. S. aureus can coat its surface w/ fibrin resisting phagocytosis
Coagulase test results
S. epidermidis = negative for coagulase production
S. aureus = positive for coagulase production
What does BEA stand for
Bile Esculin Agar
Is BEA medium selective, differential, or both?
BEA selectivity is based on
bile salt tolerance
bile salts inhibit the growth of many G+ bacteria except for Enterococci and group D streps (like S. bovis)
BEA is differential based on
hydrolysis = splitting water, so
esculin is split into glucose and esculetin
BEA tests for the presence of ?
What is the name of the indicator that combines with esculetin?
What is produced?
Why can't we test for glucose?
Esculetin combines with the indicator Ferric citrate in the medium to produce black precipitate.
We can't test for the presence of glucose because it enters glycolysis to make ATP.
Group D strep: Yes
Selective Results: + Salt tolerant (it grew)
Differential Results: Black Precipitate, esculin hydrolysis positive.
If all group D streps test positive for esculin hydrolysis, how can E. faecalis be differentiated from other group D streps?
E. faecalis is salt tolerant while other group D streps are salt intolerant
Bacitracin antibiotic sensitivity test
(Kirby Bauer Plate)
Bacitracin is an antibiotic that inhibits the growth of beta hemolytic Group A streptococci such as ______________________
It does not inhibit the growth of beta hemolytic non group A streptococci such as ___________________________
Streptococcus pyogenes - S
Streptococcus agalactiae - R
The antibiotic disc is saturated with antibiotic, but when placed on an agar surface some of the antibiotic will diffuse into the agar. If bacteria are sensitive to the antibiotic, they will not grow in its presence and there will be a __________________________ around the disc. If the bacteria are resistant to the antibiotic ____________________
zone of inhibition
they will grow right up to the edge of the disc
Optochin antibiotic sensitivity test
(Kirby Bauer Plate)
Streptococcus pneumoniae - S
Streptococcus sanguinis - R
Cells placed in hypertonic environments are in danger of __________________ water moves ______________ the cell from an area of high concentration to an area of low concentration
Typically bacteria are __________ to their environment.
Salt tolerant or intolerant:
S. aureus: tolerant
S. pyogenes: intolerant
E. faecalis: tolerant
Strep. pyogenes: GAS
Strep. agalactiae: GBS
Strep. bovis: GDS
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