Medium

• What type of medium is Mannitol Salt Agar (MSA)?

  Both selective and differential
• Which organisms does MSA select for?

  Staphylococcus species
• What does high salt concentration in MSA do to Streptococcus species?

  It selects against their growth
• What is the differential ingredient in MSA?

  Mannitol
• What happens when organisms ferment mannitol in MSA?

  They produce acidic byproducts
• What effect does the acidity from mannitol fermentation have on the pH indicator in MSA?

  It turns phenol red yellow
• Which Staphylococcus species can ferment mannitol?

  Staphylococcus aureus
• Which Staphylococcus species cannot ferment mannitol?

  Staphylococcus epidermidis
• What is the purpose of glucose broth with Durham tubes?

  To test glucose fermentation and gas production
• What does glucose broth with Durham tubes indicate about Gram-negative enteric bacteria?

  All are glucose fermenters
• What does a yellow color in glucose broth indicate?

  Glucose fermentation occurred
• Which organism is capable of fermenting glucose?

  Escherichia coli
• Which organism is a nonfermenter of glucose?

  Pseudomonas aeruginosa
• What is the end product of glycolysis?

  Pyruvic acid
• What gas do organisms produce when converting pyruvate?

  H2 and CO2
• What enzyme is involved in gas production from pyruvate?

  Formic hydrogen lyase
• How is gas detected in Durham tubes?

  As a bubble at the top
• Which organisms are gas producers in glucose broth?

  Escherichia coli and Proteus mirabilis
• What does Shigella dysenteriae do in glucose broth?

  Ferments glucose but does not produce gas
• What are the steps to interpret results from glucose broth with Durham tubes?

  • Observe color change to yellow for fermentation
  • Check for gas bubble in Durham tube
  • Identify organism based on results
• What type of medium is Blood Agar Plates (BAP)?

  Differential medium
• What does BAP test for?

  Ability to produce hemolysins
• What is beta-hemolysis?

  Complete hemolysis with a clear zone
• Which organisms are beta-hemolytic?

  Staphylococcus aureus and Streptococcus pyogenes
• What is alpha-hemolysis?

  Partial hemolysis with a green zone
• Which organisms are alpha-hemolytic?

  Streptococcus pneumoniae
• What is gamma-hemolysis?

  No hemolysis occurs
• Which organism is gamma-hemolytic?

  Staphylococcus epidermidis
• What is the purpose of the streak-stab technique?

  To detect streptolysin O
• Why is streptolysin O only seen subsurface?

  It is inactivated by O2
• What is Bile Esculin Agar used for?

  To identify Enterococcus species
• What are the selective ingredients in Bile Esculin Agar?

  Bile and sodium azide
• What happens if an organism hydrolyzes esculin in Bile Esculin Agar?

  It turns the slant dark brown to black
• What does esculetin react with in Bile Esculin Agar?

  Ferric citrate
• What does a positive result in Bile Esculin Agar indicate?

  The organism can hydrolyze esculin
• Which organism is positive for Bile Esculin Agar?

  Enterococcus faecalis
• What does a negative result in Bile Esculin Agar indicate?

  The organism cannot hydrolyze esculin
• What does an uninoculated tube in Bile Esculin Agar look like?

  It remains unchanged
• What type of medium is Sulfur Indole Motility Media (SIM)?

  Differential medium
• What does SIM test for in organisms?

  Ability to reduce sulfur, produce indole, and be motile