micro lab 10-12 Flashcards
This bacterium is the #1 most common cause of
food poisoning in our country:
Salmonella
This bacterium is #2–the second most common
cause of food poisoning in our country:
Campylobacter
Which G- rod causes a kind of food poisoning
called gastroenteritis?
Salmonella
Which G- rod causes a condition called
bacillary dysentery?
Shigella
What ingredients make MacConkey agar selective?
crystal violet and bile salts
What ingredients make MacConkey agar differential?
lactose and neutral red
What is the pH indicator used in MacConkey agar?
neutral red
MacConkey agar results:
growth and pink colonies
Conclusion?
-the bacterium must be G- because it grew
-the bacterium can break down lactose because
of the color change to pink
-the bacterium could be E. coli
MacConkey agar results:
growth and clear colonies
-the bacterium must be G- because it grew
-the bacterium cannot break down lactose because
there was no color change to pink
-the bacterum could be Salmonella enteritidis
or Pseudomonas aeruginosa
What is the pH indicator used in TSI agar?
phenol red
In a TSI slant, how do you read these test results?
Glucose Lactose/Sucrose Gas H2S gas
Glucose: the bottom of the tube turns yellow if the bacteria
can break down glucose.
Lactose/Sucrose: the slant on top turns yellow if the
bacteria can break down lactose and sucrose.
Gas: bubbles and gas pockets are seen if the bacteria
produce a lot of hydrogen gas (H2) and carbon dioxide (CO2).
H2S gas: a black color forms if the bacteria produce
H2S gas.
TSI slant results for E. coli:
Glucose
Lactose/Sucrose
Gas
H2S
E. coli:
Glucose: +
Lactose/Sucrose: +
Gas: +
H2S: -
TSI slant results:
bottom of the tube: yellow
slant: yellow
bubbles/gas pockets: yes
black color: no
The G- rod is E. coli.
TSI slant results for Salmonella enteritidis:
Glucose
Lactose/Sucrose
Gas
H2S
Salmonella enteritidis:
Glucose: +
Lactose/Sucrose: -
Gas: +
H2S: +
TSI slant results:
bottom of the tube: yellow
slant: red
bubbles/gas pockets: yes
black color: yes
The G- rod is Salmonella enteritidis.
TSI slant results: Pseudomonas aeruginosa
Glucose
Lactose/Sucrose
Gas
H2S
Pseudomonas aeruginosa:
Glucose: -
Lactose/Sucrose: -
Gas: -
H2S: -
TSI slant results:
bottom of the tube: red
slant: red
bubbles/gas pockets: no
black color: no
The G- rod is Pseudomonas aeruginosa.
Tuberculosis: cause
Mycobacterium tuberculosis
Acid-fast results: from sputum
Bacteria stained red
The patient has tuberculosis.
Acid-fast results: from sputum
bacteria stained blue
The patient has some type of pneumonia.
HIV testing: Indirect ELISA
Tests the patient for HIV antibodies in
their serum (plasma).
HIV testing: Western blot
Tests the patient for HIV epitopes in their blood.
HIV testing: Oral test
A home kit that is an indirect test. It uses a
swab specimen from the patient’s gums to
test for HIV antibodies.
HIV testing: Saliva test
A home kit that is an indirect test. It uses
a drop of saliva to test the patient for
HIV antibodies.
Alpha hemolysis: definition
Incomplete hemolysis; some RBC in the area have
been made to burst
Alpha hemolysis: appearance
It appears discolored/greenish on a blood agar plate
where the bacteria are growing.
Alpha hemolysis: example
Streptococcus pneumoniae
Beta hemolysis: definition
Complete hemolysis: all RBCs in the area have
been made to burst.
Beta hemolysis: appearance
It appears clear on a blood agar plate where the
bacteria are growing.
Beta hemolysis: example
Streptococcus pyogenes
Nonhemolytic: definition
The bacteria do no hemolysis at all;
no RBCs are made to burst.
Nonhemolytic: appearance
It still appears blood red on a blood agar plate
where the bacteria are growing.
Nonhemolytic: example
Enterococcus
Gram stain: Streptococcus pneumoniae
G+ coccus in pairs
Gram stain: Streptococcus pyogenes
G+ coccus in chains
Gram stain: Enterococcus
G+ coccus in chains
Optochin test: clear zone
It is Streptococcus pneumoniae
Optochin test: no clear zone
It is not Streptococcus pneumoniae.
Streptococcus pneumoniae: clinical significance
pneumonia, meningitis, middle ear infections
Bacitracin test: clear zone
It is Streptococcus pyogenes
Bacitracin test: no clear zone
It is not Streptococcus pyogenes.
Streptococcus pyogenes: clinical significance
Strep throat, scarlet fever, Rheumatic fever
Bile esculin test: growth, black
It is Enterococcus.
Bile esculin test: no growth, no black
It is not Enterococcus.
Enterococcus: clinical significance
UTI, Bacterial endocarditis
Mannitol Salt agar: What ingredient(s) make it selective?
Salt (NaCl)
Mannitol Salt agar: What ingredient(s) make it differential?
Mannitol sugar, phenol red
Mannitol Salt agar results:
-Growth, stays red
-It must be a Staphylococcus because it grew
-It cannot break down mannitol sugar because it did not turn yellow.
-It must be Staphylococcus epidermidis.
Mannitol Salt agar results:
Growth, turned yellow
-Must be a Staphylococcus because it grew
-It can break down mannitol sugar because it
did turn yellow.
-It could be Staphylococcus aureus or Staphylococcus saprophyticus
Gram stain: Staphylococcus epidermidis,
Staphylococcus aureus,
Staphylococcus saprophyticus
All species of Staphylococcus are a G+ coccus in clusters.
Staphylococcus epidermidis: Mannitol Salt agar results
-It grows because it is a Staphylococcus
-It stays red because it cannot break down Mannitol sugar
Staphylococcus epidermidis: clinical significance
UTI and blood infections
Staphylococcus aureus: Mannitol Salt agar results
-It grows because it is a Staphylococcus
-It turns yellow because it can break down mannitol sugar
Staphylococcus aureus: Coagulase
Staphylococcus aureus is the only Staph that produces the
enzyme coagulase, which makes plasma clot.
Coagulase test results: plasma clotted
It is Staphylococcus aureus
Coagulase test results: plasma not clotted
It could be Staphylococcus epidermidis or
Staphylococcus saprophyticus
Staphylococcus aureus: clinical significance
pimples, boils, skin abscess, food poisoning,
pneumonia, blood infections
Staphylococcus saprophyticus: Mannitol Salt agar results
-It grows because it is a Staphylococcus.
-It turns yellow because it can break down Mannitol sugar
Novobiocin test: clear zone
It could be Staphylococcus epidermidis or
Staphylococcus aureus.
Novobiocin test: no clear zone
It must be Staphylococcus saprophyticus.
Staphylococcus saprophyticus: clinical significance
UTI in females
