Microbiology Exam Review Flashcards

McConkey’s Agar Test

• Most solid differential medium.
• Used to identify lactose-fermenting organisms.
• Results:
  • +/pink: Fermentation, Gram-negative rods.
  • +/beige: Non-fermentation, Gram-negative rods.
  • -: No growth, Gram-positive.
• Substrate: Lactose.
• Enzyme: Lactase.
• Products: Galactose, glucose, and lactic acid.
• Selective Agents: Bile salts, crystal violet, and neutral red pH indicator.
• Positive Organisms:
  • Escherichia coli
  • Pseudomonas fluorescens
  • Serratia marcescens
  • Enterobacter aerogenes
  • Salmonella enterica

Columbia CNA Agar Test

• Inhibits Gram-negative bacteria.
• Both selective and differential blood agar.
• Three hemolysis patterns:
  • Alpha: Olive.
  • Beta: Clear.
  • Gamma: No change in media color + colonies.
• Substrate: RBC and blood protein.
• Enzyme: Alpha, beta, and gamma hemolysins.
• Products: Amino acids.
• Selective Agents: Nalidixic acid and colistin.
• Positive Organisms:
  • Enterococcus durans (beta / gamma)
  • Staphylococcus epidermidis (gamma)
  • Neisseria sicca (gamma)
  • Staphylococcus aureus (beta)
  • Streptococcus pyogenes (beta)

Carbohydrate Test

• Composed of carbon, hydrogen, and oxygen.
• Results:
  • Red and no tube displacement: - \text{acid}/ - \text{gas}
  • Yellow and no tube displacement: + \text{acid}/ - \text{gas}
  • Yellow and tube displacement: + \text{acid}/ + \text{gas}
• Substrates: Lactose, glucose, and sucrose.
• Enzymes: Vary.
• Product: General acid.
• Indicator: Phenol red.
• Differential Agent: Lactose, glucose, and sucrose.
• Selective Agent: None.
• Positive Organisms:
  • Escherichia coli (+ \text{gluc}, + \text{gas}/ + \text{lac}, + \text{gas}/ + \text{suc}, + \text{gas})
  • Enterococcus durans (+ \text{gluc}, - \text{gas}/ +\text{lac}, - \text{gas}/ + \text{suc}, - \text{gas})
  • Serratia marcescens (+ \text{gluc}, +/- \text{gas}/ - \text{lac}, - \text{gas}/ + \text{suc}, +/- \text{gas})
  • Staphylococcus epidermidis (+ \text{gluc}, + \text{gas}/ + \text{lac}, + \text{gas}/ + \text{suc}, + \text{gas})
  • Neisseria sicca (+ \text{gluc}, - \text{gas}/ - \text{lac}, - \text{gas}/ + \text{suc} - \text{gas})
  • Salmonella enterica (+ \text{gluc}, + \text{gas}/ - \text{lac}, - \text{gas}/ - \text{suc}, - \text{gas})

Indole Test

• Substrate: Tryptophan.
• Enzyme: Tryptophanase.
• Product: Indole, pyruvic acid, and ammonia.
• Indicator: Kovac's reagent (red ring).
• Differential Agent: Tryptophan.
• Selective Agent: None.
• Results:
  • Red ring: Positive indole reaction.
  • Yellow/beige ring: Negative reaction.
• Positive Organism: Escherichia coli.

Methyl Red Test

• Substrate: Glucose.
• Enzyme: Many.
• Product: Acidic/many.
• Indicator: Methyl red.
• Differential Agent: Glucose.
• Selective Agent: None.
• Results:
  • Red color: Positive result.
  • Yellow/orange color: Negative result.
• Positive Organisms:
  • Escherichia coli
  • Salmonella enterica
  • Serratia marcescens

Voges-Proskauer Test

• Substrate: Glucose.
• Enzyme: Many.
• Product: Acetoin and butanediol.
• Indicator: Barrett’s A&B.
• Differential Agent: Glucose.
• Selective Agent: None.
• Results:
  • Clear: Negative result.
  • Intense rose color: Positive result.
• Positive Organism: Enterobacter aerogenes.

Citrate Test

• Substrate: Citrate.
• Enzyme: Citrase.
• Product: Pyruvic acid, acetic acid, and carbon dioxide.
• Indicator: Bromthymol blue (agar changes from green to blue).
• Differential Agent: Citrate.
• Selective Agent: None.
• Results:
  • Blue: Positive result.
  • Green: Negative result.
• Positive Organisms:
  • Enterobacter aerogenes
  • Serratia marcescens
  • Pseudomonas fluorescens

Bile Esculin Test

• Results:
  • Black streak line: Positive.
  • Clear streak line: Negative.
• Substrate: Esculin.
• Enzymes: Many.
• Products: Glucose, esculetin, and Fes?
• Indicator: Ferric ammonia citrate/ black colonies.
• Differential Agent: Esculin.
• Selective Agent: Bile salt.
• Positive Organisms:
  • Escherichia coli (+)
  • Enterococcus durans (+)
• Negative Organisms:
  • Pseudomonas fluorescens (-)
  • Micrococcus luteus (-)

DNAse Agar Test

• Substrate: DNA.
• Enzyme: DNAse.
• Product: Oligonucleotides.
• Indicator: Methyl green DNA stain.
• Differential Agent: DNA.
• Selective Agent: None. *Positive Organisms:
  • Serratia marcescens (+)
    *Negative Organisms:
  • Eschericia coli (-)
  • Salmonella enterica (-)
  • Staphylococcus epidermis (-)

Oxidase Test

• Substrate: Naphthol.
• Enzyme: Cytochrome oxidase.
• Product: Indophenol blue.
• Indicator: Phenylenediamine/ blue color on the swab.
• Differential Agent: Naphthol.
• Selective Agent: None. *Positive Organism:
  • Micrococcus luteus (+)
  • Enterococcus durans (+)
    *Negative Organisms:
  • Eschericia coli (-)
  • Neisseria sicca (-/+)
  • Pseudomonas fluorescens (-)

Nitrogen Test (Nitrate Reduction Test)

• Substrate: NO3 from KNO3 broth.
• Enzymes: Nitrate and nitrite reductase.
• Product: Sulfobenzene.
• Indicator: Sulfonic acid, naphthylamine, and zinc.
• Differential Agent: NO_3.
• Selective Agent: None. *Positive Organisms:
  • Escherichia coli (+ nitrate reductase/ - nitrite reductase)
  • Pseudomonas fluorescens (+ nitrate reductase/ + nitrite reductase)
  • Enterobacter aerogenes (+ nitrate reductase/ - nitrite reductase)
  • Staphylococcus epidermidis (+ nitrate reductase/ - nitrite reductase)
  • Enterococcus durans (+ nitrate reductase/ - nitrite reductase)

Catalase Test

• Substrate: Hydrogen peroxide (H2O2).
• Enzyme: Catalase.
• Product: H2O + O2.
• Indicator: No bubbles = negative/ bubbles = positive.
• Differential Agent: H2O2.
• Selective Agent: None. *Positive Organisms:
  • Staphylococcus epidermidis (+)
  • Micrococcus luteus (+)
  • Staphylococcus aureus (+)
  • Bacillus subtilis (+)

Mannitol Salt Agar Test

• Substrate: Mannitol sugar.
• Enzyme: Mannitol dehydrogenase.
• Products: Pyruvic acid.
• Indicator: Phenol red pH.
• Selective Agent: NaCl 8%.
• Differential Agent: Mannitol. *Results *yellow= + growth/ + ferm
  • pink= + growth/ - negative ferm
    *Positive Organisms:
  • Staphylococcus epidermidis ( + growth/ - fermentation)
    *Negative Organisms:
  • Micrococcus luteus (- growth/ - fermentation)
  • Staphylococcus aureus (+ growth/ + fermentation)

Coagulase Test

• Substrate: Prothrombin.
• Enzyme: Coagulase.
• Product: Fibrin.
• Indicator: Hard nodule/ mass= +.
• Differential Agent: Prothrombin.
• Selective Agent: None. *Results:
  • foggy= + result
  • clear= - result
    *Positive Organisms:
  • Staphylococcus aureus (+)
    *Negative Organisms:
  • Staphylococcus epidermidis (-)
  • Micrococcus luteus (-)