Selective and Differentials

PEA Ingredients

Phenyethyl alcohol

PEA (Selective Only)

Inhibits gram negative

PEA Selective Results

Colonies should be gram positive (p)

CNA Ingredients

• Antibiotics

  • Colistin

  • Nalidixic Acid

• Sheep blood

CNA Selective and Differential

• Selective: Inhibits gram negative

• Differential: ability to hemolyze

CNA Selective Results

Colonies should be gram positive ©

CNA Differential Results

• Clearing of media = beta hemolysis = full breakdown of red blood cells

• Greening of media = alpha hemolysis = partial breakdown of RBC

• No change in media = gamma hemolysis = no breakdown of RBC

MSA Ingredients

• Mannitol

• Sodium Chloride (NaCl)

MSA Selective and Differentials

• Selective: Inhibits non-osmotolerant bacteria

• Differential: ability to ferment mannitol

MSA Selective Results

Colony growth should indicate Staphylococcus

MSA Differential Results

• Yellow media = ferments mannitol = probable S. aureus

• Pink/red media = does not ferment mannitol = Staphylococcus other than S. areus

BEA Ingredients

• Bile

• Esculin

BEA Selective and Differential

• Selective: Inhibits gram positive

• Differential: ability to break down esculin

BEA Selective Results

Colonies should be gram negative (b)

BEA Differential Results

• Darkening of media = break down of esculin = probable member of Group D Staphylococcus, Streptococcus, or Enterococcus

• No darkening of media = does not break down esculin = not a member of Group D Staphylococcus, Streptococcus, or Enterococcus

MAC Ingredients

• Bile salts

• Lactose

• Crystal violet

• Neutral red

MAC Selective and Differential

• Selective: Inhibits gram positive

• Differential: ability to ferment lactose

MAC Selective Results

Colonies should be gram negative (m)

MAC Differential Results

• Pink to red growth = lactose fermentation = probable coliform

• Colorless growth = no lactose fermentation = noncoliform

EMB Ingredients

• Lactose

• Eosin

• Methylene Blue

EMB Selective and Differential

• Selective: Inhibits gram positive

• Differential: ability to ferment lactose

EMB Selective Results

Colonies should be gram negative (e)

EMB Differential Results

• “Dark” growth (purple to black with or without green metallic) = Ferments lactose with acid production = probable coliform

• Pink growth = ferments lactose with little acid production = possible coliform

• Colorless growth = does not ferment lactose = noncoliform