Microbiology Lab Exam 1 Questions and
Answers Graded A+
What does a positive result in a TSI (Triple Sugar Iron) test look like for glucose fermentation?
✔✔The butt of the tube turns yellow, indicating glucose fermentation and acid production.
What is the result of a positive test for urease activity?
✔✔The medium turns pink, indicating that the bacterium produces urease and hydrolyzes urea.
What does a positive catalase test look like?
✔✔Bubbles appear when hydrogen peroxide is applied to the bacterial culture, indicating the
presence of catalase.
What is the appearance of a positive phenol red sugar fermentation test?
✔✔The medium changes color to yellow, indicating acid production from sugar fermentation.
What is the significance of the coagulase test?
✔✔It is used to identify Staphylococcus aureus by its ability to coagulate plasma.
1
,What is the purpose of the bile esculin test?
✔✔To differentiate Enterococcus species from other Gram-positive cocci based on their ability
to hydrolyze esculin in the presence of bile.
What does a positive Voges-Proskauer test show?
✔✔A red color develops, indicating the bacterium ferments glucose to acetoin, which is further
metabolized to a neutral product.
What does a positive nitrate reduction test show?
✔✔A red color develops, indicating that nitrate has been reduced to nitrite or nitrogen gas by the
bacterium.
What does a positive starch hydrolysis test show?
✔✔A clear zone around the bacterial growth indicates that the bacterium produces amylase and
can hydrolyze starch.
What is the purpose of a Gram stain in microbiology?
✔✔To differentiate bacterial species into Gram-positive or Gram-negative based on the cell wall
structure.
2
,What is the difference between a positive and negative catalase test?
✔✔A positive catalase test produces bubbles when hydrogen peroxide is applied, indicating the
presence of catalase enzyme.
What does a positive result in a coagulase test indicate?
✔✔It indicates that the bacterium produces coagulase, which causes blood plasma to clot.
What is the function of bacterial pili?
✔✔Pili are used for adhesion to surfaces and genetic exchange during conjugation.
What is a characteristic feature of Gram-positive bacteria?
✔✔They have a thick peptidoglycan layer that retains the crystal violet stain, appearing purple
under the microscope.
What does a positive result for an oxidase test look like?
✔✔A positive result produces a purple color within seconds, indicating the presence of
cytochrome c oxidase.
3
, What is the appearance of a positive phenol red fermentation test?
✔✔The medium changes from red to yellow, indicating acid production from fermentation.
What does a positive result in a motility test indicate?
✔✔The bacterium is able to move throughout the medium, causing cloudiness beyond the
inoculation line.
What is the purpose of a MacConkey agar plate?
✔✔To differentiate bacteria based on their ability to ferment lactose and to select for Gram-
negative bacteria.
What is the result of a positive starch hydrolysis test?
✔✔A clear zone around the bacterial growth indicates the hydrolysis of starch by amylase.
What does a positive methyl red test indicate?
✔✔The bacterium performs mixed-acid fermentation, lowering the pH and turning the medium
red.
4
Answers Graded A+
What does a positive result in a TSI (Triple Sugar Iron) test look like for glucose fermentation?
✔✔The butt of the tube turns yellow, indicating glucose fermentation and acid production.
What is the result of a positive test for urease activity?
✔✔The medium turns pink, indicating that the bacterium produces urease and hydrolyzes urea.
What does a positive catalase test look like?
✔✔Bubbles appear when hydrogen peroxide is applied to the bacterial culture, indicating the
presence of catalase.
What is the appearance of a positive phenol red sugar fermentation test?
✔✔The medium changes color to yellow, indicating acid production from sugar fermentation.
What is the significance of the coagulase test?
✔✔It is used to identify Staphylococcus aureus by its ability to coagulate plasma.
1
,What is the purpose of the bile esculin test?
✔✔To differentiate Enterococcus species from other Gram-positive cocci based on their ability
to hydrolyze esculin in the presence of bile.
What does a positive Voges-Proskauer test show?
✔✔A red color develops, indicating the bacterium ferments glucose to acetoin, which is further
metabolized to a neutral product.
What does a positive nitrate reduction test show?
✔✔A red color develops, indicating that nitrate has been reduced to nitrite or nitrogen gas by the
bacterium.
What does a positive starch hydrolysis test show?
✔✔A clear zone around the bacterial growth indicates that the bacterium produces amylase and
can hydrolyze starch.
What is the purpose of a Gram stain in microbiology?
✔✔To differentiate bacterial species into Gram-positive or Gram-negative based on the cell wall
structure.
2
,What is the difference between a positive and negative catalase test?
✔✔A positive catalase test produces bubbles when hydrogen peroxide is applied, indicating the
presence of catalase enzyme.
What does a positive result in a coagulase test indicate?
✔✔It indicates that the bacterium produces coagulase, which causes blood plasma to clot.
What is the function of bacterial pili?
✔✔Pili are used for adhesion to surfaces and genetic exchange during conjugation.
What is a characteristic feature of Gram-positive bacteria?
✔✔They have a thick peptidoglycan layer that retains the crystal violet stain, appearing purple
under the microscope.
What does a positive result for an oxidase test look like?
✔✔A positive result produces a purple color within seconds, indicating the presence of
cytochrome c oxidase.
3
, What is the appearance of a positive phenol red fermentation test?
✔✔The medium changes from red to yellow, indicating acid production from fermentation.
What does a positive result in a motility test indicate?
✔✔The bacterium is able to move throughout the medium, causing cloudiness beyond the
inoculation line.
What is the purpose of a MacConkey agar plate?
✔✔To differentiate bacteria based on their ability to ferment lactose and to select for Gram-
negative bacteria.
What is the result of a positive starch hydrolysis test?
✔✔A clear zone around the bacterial growth indicates the hydrolysis of starch by amylase.
What does a positive methyl red test indicate?
✔✔The bacterium performs mixed-acid fermentation, lowering the pH and turning the medium
red.
4
