assignment of class

1. MacConkey Agar

2. What is MacConkey Agar
 MacConkey agar (MAC) was the first solid
differential media to be formulated which was
developed at 20th century by Alfred Theodore
MacConkey.
 MacConkey agar is a selective and differential media
used for the isolation and differentiation of non-
fastidious gram-negative rods, particularly members
of the family Enterobacteriaceae and the
genus Pseudomonas.
 Neutral red is the PH indicator

3. Composition of MacConkey Agar
ingredients amount
Peptone (pancreatic digest of gelatin ) 17 gm
Proteose peptone (meat and casein ) 3gm
Lactose monohydrate 1o gm
Bile salts 1.5gm
Sodium chloride 5gm
Neutral red 0.03gm
Crystal Violet 0.001g
Agar 13.5gm
Distilled Water Add to make 1 liter

5. USES OF MacConkey Agar
 MacConkey agar is used for the isolation of gram-
negative enteric bacteria.
 It is used in the differentiation of lactose fermenting
from lactose non-fermenting gram-negative bacteria.
 It is used for the isolation of coli forms and intestinal
pathogens in water, dairy products and biological
specimens.

7. Preparation of MacConkey Agar
1. Suspend 49.53 grams of dehydrated medium in 1000
ml purified/distilled water.
2. Heat to boiling to dissolve the medium completely.
3. Sterilize by autoclaving at 15 lbs pressure (121°C) for
15 minutes.
4. Cool to 45-50°C.
5. Mix well before pouring into sterile Petri plates.

9. Result Interpretation on MacConkey Agar
 Lactose fermenting strains
grow as red or pink and may be
surrounded by a zone of acid
precipitated bile.
 The red colour is due to production
of acid from lactose, absorption of
neutral red and a subsequent colour change of the dye
when the pH of medium falls below 6.8.

10. CONTD…
•Lactose non-fermenting
strains, such as Shigella
and Salmonella are
colourless and transparent
and typically do not alter
appearance of the medium.
•Yersinia enterocolitica may appear as small, non-
lactose fermenting colonies after incubation at room
temperature.

12. Some lactose fermenting
organism
Some non-lactose
fermenting organism
E.Coli Salmonella species
Enterococci Shigella species
K.Pneumoniae Proteus species
Y.Enterocolitica
NOTE
Bacteria which do not grow on MacConkey agar include
Streptococcus Pyogenes, Streptococcus Pneumoniae,
Viridans streptococci , and Pasteurella species

14. Quality control
 The quality control is tested with at least one known
organism to demonstrate growth or positive reaction
and at least one organism to demonstrate inhibition or
negative reaction

15. Contd…
Control Organism Expected Results
E. coli (ATCC 25922) Pink colonies
Staphylococcus aureus (ATCC 25923) Growth
Streptococcus faecalis (ATCC 29212) Growth with magenta pink
Colonies Proteus mirabilis (ATCC 12453 ) No swarming
Beta haemolytic Streptococcus No growth