Microbiology Lab Practical Exam
Study Guide
• What are EMB and McConkey Agar selective for? -✓✓Gram Negative Bacteria
• How does EMB agar select gram negative bacteria? -✓✓it uses eosin and
methylene blue dyes to inhibit the growth of gram positive bacteria
• How does McConkey agar select gram negative bacteria? -✓✓it uses blue salts
and crystal violet dyes to inhibit the growth of gram positive bacteria
• What are EMB and McConkey Agar differential for? -✓✓lactose and non-
lactose fermenters
• How does EMB agar differentiate between lactose and non-lactose fermenters?
-✓✓it uses lactose as its medium and when the acid is fermented, the dyes react
on the colony surface, coloring it and eosin and methylene blue inhibit gram
positive bacteria
• How does McConkey agar differentiate between lactose and non-lactose
fermenters? -✓✓the medium contains a natural pH red dye and lactose and
when lactose is fermented, the clear colonies become pink on the agar and crystal
violet and bile salts inhibit gram positive bacteria
• How many colonies are on a countable plate? -✓✓between 30-300 CFUs
, • NON-LACTOSE FERMENTERS on the EMB and McConkey agars appear
____________________. -✓✓Colorless
• On EMB agar, LACTOSE FERMENTERS appear ____________________ (small
and large acid production). -✓✓Metallic Green for large acid production Purple
for small acid production
• Beta-hemolysis (complete cell lysis) -✓✓Clearing around growth
• Alpha-hemolysis (partial cell lysis) -✓✓Greening around growth
• Gamma-hemolysis (no cell lysis) -✓✓No change in the medium
• Positive Result For Catalase Test -✓✓Bubbles
• Negative Result For Catalase Test -✓✓No Bubbles
• Positive Result For Coagulase Test -✓✓Plasma forms a clot
• Negative Result For Coagulase Test -✓✓Plasma remains liquid
• Positive Result For Gelatin Liquidification Test -✓✓Gelatin Liquified
• Negative Result For Gelatin Liquidification Test -✓✓Gelatin remained solid
Study Guide
• What are EMB and McConkey Agar selective for? -✓✓Gram Negative Bacteria
• How does EMB agar select gram negative bacteria? -✓✓it uses eosin and
methylene blue dyes to inhibit the growth of gram positive bacteria
• How does McConkey agar select gram negative bacteria? -✓✓it uses blue salts
and crystal violet dyes to inhibit the growth of gram positive bacteria
• What are EMB and McConkey Agar differential for? -✓✓lactose and non-
lactose fermenters
• How does EMB agar differentiate between lactose and non-lactose fermenters?
-✓✓it uses lactose as its medium and when the acid is fermented, the dyes react
on the colony surface, coloring it and eosin and methylene blue inhibit gram
positive bacteria
• How does McConkey agar differentiate between lactose and non-lactose
fermenters? -✓✓the medium contains a natural pH red dye and lactose and
when lactose is fermented, the clear colonies become pink on the agar and crystal
violet and bile salts inhibit gram positive bacteria
• How many colonies are on a countable plate? -✓✓between 30-300 CFUs
, • NON-LACTOSE FERMENTERS on the EMB and McConkey agars appear
____________________. -✓✓Colorless
• On EMB agar, LACTOSE FERMENTERS appear ____________________ (small
and large acid production). -✓✓Metallic Green for large acid production Purple
for small acid production
• Beta-hemolysis (complete cell lysis) -✓✓Clearing around growth
• Alpha-hemolysis (partial cell lysis) -✓✓Greening around growth
• Gamma-hemolysis (no cell lysis) -✓✓No change in the medium
• Positive Result For Catalase Test -✓✓Bubbles
• Negative Result For Catalase Test -✓✓No Bubbles
• Positive Result For Coagulase Test -✓✓Plasma forms a clot
• Negative Result For Coagulase Test -✓✓Plasma remains liquid
• Positive Result For Gelatin Liquidification Test -✓✓Gelatin Liquified
• Negative Result For Gelatin Liquidification Test -✓✓Gelatin remained solid
