BMS 127 Selective and Differential Agars

Question 0

What does Xylose Lysine Deoxycholate (XLD) agar differentiate?

Answer 0

Detects sugar fermentation and lysine decarboxylate.

Salmonella = red colonies with black centers
Shigella = red colonies
E. coli = yellow to orange colonies
P. aeruginosa = pink, flat, rough colonies

Question 1

What does Bile Esculin agar differentiate?

Answer 1

Enterococcus vs. Staphylococcus.

Enterococcus turns the medium black

Question 2

What does Eosin Methylene Blue agar detect?

Answer 2

Selects for Gram-negative bacteria, differentiates between Lac +/- and E.coli

Lac+ = purple-black colonies
Lac- = clear colonies (Shigella, Salmonella)
E. coli = metallic green colonies

Question 3

What does Hektoen Enteric agar detect?

Answer 3

Used to identify Salmonella and Shigella from patient specimens. Inhibits Gram-positive bacteria, contains indicators for Lactose fermentation and H2S production.

Salmonella = black colonies
Shigella = translucent green colonies

Question 4

What is MacConkey agar used for?

Answer 4

Used to grow lactose fermenting Gram-negative bacteria.

Lac+ = red/pink colonies
Lac- = white/colorless colonies with gold or brown centers

Question 5

What does a TSI slant detect?

Answer 5

A TSI slant can detect sugar fermentation, gas production and H2S production.

yellow butt/red slant = acid butt/alkaline slant = only glucose fermented
yellow butt/yellow slant = glucose + another sugar fermented
red butt/red slant = no sugar fermentation
fractures = gas production
black butt = H2S production

Question 6

What are the three possible results from a blood agar hemolysis test?

Answer 6

yellow border = beta hemolysis (complete)
green border = alpha hemolysis (incomplete)
no border = gamma hemolysis (none)

Question 7

What does a starch plate detect the presence of?

Answer 7

amylase

Question 8

What does a triglyceride plate detect the presence of?

Answer 8

lipase

Question 9

What does a casein plate detect the presence of?

Answer 9

protease