Practical Testing and Agar

Question 1

Blood Agar

Answer 1

Differential
nutrient-rich blood supplement that discolours in the presence of Haemolysins
differentiates bacteria on their haemolytic ability

alpha
beta
gamma

Colonies form which require additional nutrients from the blood

Question 2

CLED
Cystine-Lactose-Electrolyte Deficient

Answer 2

Differential and Partially Selective
inhibits gram-pos
contains lactose indicators - differentiates between fermenting () and non-fermenting () gram-negs
== if fermenting is present, acidic products form, causing colour change

USED FOR UTIs

Question 3

MacConkey agar

Answer 3

Differential and Selective
for Enterobacteriaceae
selective agents inhibit gram-pos
bile salts + crystal violet = gram-neg
lactose and pH indicators = differentiate between lactose-fermentors and non-fermentors ()
fermentors = pink colonies
non = colourless

GIT INFECTIONS

Question 4

Pseudomonas Centrimide agar (PCA)

Answer 4

Differential and selective
for Pseudomonas aeruginosa
Cetrimide = selective agent = P.a has the ability to modify its outer-membrane to resist centrimide
BLUE/GREEN colonies

UTIs

Question 5

Muller Hinton

Answer 5

Not differential or selective
USED FOR AST
all can grow

Question 6

Sulfide indole motility medium (SIM)

Question 7

Mannitol Salt agar (MSA)

Answer 7

7.5% NaCl
Selective and Differential
colour change red to yellow if the bacteria produces _ to ferment the mannitol

S. aureus