Exercise 6 Selective and Differential Media: Results and Colors in Agar

UWhat does a positive growth and negative lactose fermentation result on MacConkey agar indicate?

Non-lactose fermenting Enterobacteriaceae

What does a positive growth and positive lactose fermentation result on MacConkey agar indicate?

Lactose-fermenting Enterobacteriaceae = coliform

What does no growth on MacConkey agar indicate?

Gram-positive or nonenteric

What does positive growth and positive mannitol fermentation on MSA indicate?

Pathogenic species of Staphylococcus

What does positive growth and negative mannitol fermentation on MSA indicate?

Nonpathogenic species of Staphylococcus

What does no growth on MSA indicate?

Not a species of Staphylococcus or Micrococcus

What does alpha hemolysis on Blood Agar indicate?

Partial lysis of red blood cells, indicating the presence of some Streptococcus species.

What does beta hemolysis on Blood Agar indicate?

Complete lysis of red blood cells, indicating the presence of pathogenic Streptococcus species.

What does nonhemolytic growth on Blood Agar indicate?

No hemolysis

What does alpha hemolysis on Columbia CNA with Blood Agar indicate?

Alpha hemolysis

What does growth on Columbia CNA with Blood Agar indicate?

Gram-positive

What does no growth on Columbia CNA with Blood Agar indicate?

Gram-negative

What does positive growth and positive lactose fermentation on EMB agar indicate?

Lactose-fermenting Enterobacteriaceae = coliform

What is a coliform?

A lactose-fermenting Enterobacteriaceae

What does positive growth and negative lactose fermentation on EMB agar indicate?

Non-lactose fermenting Enterobacteriaceae

What does a green metallic sheen on EMB agar indicate?

Escherichia coli

What does no growth on EMB agar indicate?

Gram-positive or nonenteric

What does lactose fermentation indicate on MacConkey, EMB, or HEA agar?

Lactose-fermenting Enterobacteriaceae = coliform

What does positive growth and positive lactose fermentation on HEA indicate?

Lactose-fermenting Enterobacteriaceae = coliform

What does positive growth and negative lactose fermentation on HEA indicate?

Non-lactose fermenting Enterobacteriaceae

What do black centers on non-lactose fermenting colonies on HEA indicate?

H2S producer

What does no growth on HEA indicate?

Gram-positive or nonenteric

Pink/Red Colonies in McConkey Agar:

Lactose fermenters (examples: Escherichia coli, Klebsiella, and Enterobacter).

Colorless/Transparent Colonies in McConkey Agar:

Non-lactose fermenters (examples: Salmonella and [Shigella]).

No growth in McConkey Agar:

Gram-positive bacteria are blocked by crystal violet and bile salts in the agar.

Yellow Colonies/Agar on MSA:

Mannitol fermenters that produce acid (pathogenic)

Pink/RedColonies on MSA:

Nonpathogenic species of Staphylococcus

Green Metallic Sheen Colonies on EMB:

Positive for Growth, Positive for Lactose Fermentation, Lactose Fermenting Enterobacteriaceae = Coliform (Escherichia coli)

Dark Purple / Black / Pink Colonies on EMB:

Positive for Growth, Positive for Lactose Fermentation, Lactose Fermenting Enterobacteriaceae = Coliform

Colorless / Amber Colonies on EMB:

Positive for Growth, Negative for Lactose Fermentation, Non-Lactose Fermenting Enterobacteriaceae

No Growth on EMB:

Gram-positive or Nonenteric organism (inhibited by eosin and methylene blue dyes)

Yellow / Orange to Salmon-PinkColonies on HE Agar:

Positive for Growth, Positive for Lactose Fermentation, Lactose Fermenting Enterobacteriaceae = Coliform

Blue-Green / Green Colonies (without black centers) on HE Agar:

Enterobacteriaceae (e.g., Shigella)

Blue-Green / Green with Black Centers (or completely black) on HE Agar:

Positive for Growth, Negative for Lactose Fermentation, Non-Lactose Fermenting Enterobacteriaceae, Black Centers = H2S (Hydrogen Sulfide) Producer (e.g., Salmonella)

No Growth on HE Agar:

Gram-positive or Nonenteric organism (inhibited by bile salts)