What is MacConkey Broth?
MacConkey Broth is a modification of the medium developed by scientist MacConkey. MacConkey Broth is used for the cultivation of gram-negative Bacteria.

Storage of MacConkey’s Broth
- MacConkey’s Broth medium should be kept upright at 2-30 °c.
- Adequate storage definitely increases the life and quality of the product.
- Freezing and overheating will cause the scale to deteriorate of the medium.
- MacConkey’s Broth should not be used beyond the expiration date.
- Expiration dates apply to tubes and packages that can be opened, adequately stored.
Composition of MacConkey Broth
- Peptone – 20 gm
- Sodium taurocholate – 5 gm
- Lactose – 10 gm
- Sodium chloride (NaCl) – 5 gm
- pH – 7.2
- Distilled water – 1 liter
- Neutral red (1% sol.) – 4 ml
Ingredients | Amount |
---|---|
Peptone | 20 gm |
Sodium taurocholate | 5 gm |
Lactose | 10 gm |
Sodium chloride (NaCl) | 5 gm |
Neutral red (1%) | 4 ml |
Distilled Water | 1 Liter (As our need) |
Preparation of MacConkey broth
- The dye should be added only after adjusting the pH.
- Distribute 10 ml in different test tubes.
- Put Durham’s tubes in an inverted position in these tubes.
- Sterilize by autoclaving at 121 °c for 15 minutes.
What is MacConkey agar?
- MacConkey agar (MAC) is a solid differential media.
- This agar is developed in the 20th century by Alfred Theodore MacConkey.
- It is a solidifying agent which solidifies the liquid medium.
Composition of MacConkey agar
- Peptone – 20 gm
- Sodium taurocholate – 5 gm
- Lactose – 10 gm
- Sodium chloride (NaCl) – 5 gm
- Distilled water – 1 liter
- pH – 7.2
- Neutral red (1% sol.) – 4 ml
- Agar – 2-3%
Ingredients | Amount |
---|---|
Peptone | 20 gm |
Sodium taurocholate | 5 gm |
Lactose | 10 gm |
Sodium chloride (NaCl) | 5 gm |
Neutral red (1%) | 4 ml |
Agar (2-3%) | 13.5 gm |
Distilled Water | 1 Liter (As our need) |
Preparation of MacConkey agar
- Sterilize by autoclaving at 121 °c for 15 minutes.
- The method of plates preparation is the same as that of Nutrient agar. This medium is used for the cultivation of enteric bacteria.
- Sodium taurocholate ( bile salt) inhibits non-enteric bacteria. The lactose fermenters ( E.coli, Klebsiella spp.) utilize lactose in the medium and produce acid and gas.
- Acid production changes colour from neutral red to pink and gas production is detected in inverted Durham’s tubes in MacConkey’s broth tubes.
- In MacConkey’s agar plates color of colonies of lactose fermenting organisms are pink and are opaque as at acidic pH, neutral red precipitates in the colony.
- Lactose non-fermenters (Salmonella spp. and Vibrio spp.)show no pink coloration around the colony, in fact, the medium changes the colour to yellow and the colonies remain translucent.
Uses of MacConkey agar
- MacConkey agar is used in selective and differential media for the isolation and differentiation of non-fastidious gram-negative rod-shaped bacteria, particularly members of the family Enterobacteriaceae and the genus Pseudomonas.
- It is also used for the differentiation of lactose fermenting from lactose non-fermenting gram-negative bacteria.
- MacConkey agar is used for the isolation as well as differentiation of gram-negative bacteria.
Limitations of MacConkey Agar
- Some strains may be encountered that grow poorly or fail to grow on this medium.
- Some strains may swarm on MacConkey Agar medium.
Result and Observation of MacConkey Agar

“Lactose fermenting strains, grow red or pink and may be surrounded by a zone of acid precipitated bile. The red colour is due to the production of acid from lactose, absorption of neutral red, and a subsequent colour change of the dye when the pH of the medium falls below 6.8.”
“Lactose non-fermenting strains, such as Shigella and Salmonella are colourless and transparent and typically do not alter the appearance of the medium. Yersinia enterocolitica may appear as small, non-lactose fermenting colonies after incubation at room temperature.”
Reference and Sources
- http://www.cabri.org/guidelines/micro-organisms/M203Ap1.html
- https://microbiologyinfo.com/macconkey-agar-composition-principle-uses-preparation-and-colony-morphology
- https://en.wikipedia.org/wiki/MacConkey_agar
- https://microbeonline.com/macconkey-agar-mac-composition-preparation-uses-and-colony-characteristics
- https://www.carlroth.com/com/en/media-for-salmonella-shigella/macconkey-agar/p/x922.1
Further Readings
- Acid fast staining of bacteria
- Algae
- Aseptic Transfer Technique
- Bacterial Flagella, Fimbriae and Pili
- Bacterial Growth and Nutrition
- Extremophiles
- Fimbriae vs Flagella
- Fimbriae vs Pili
- Growth Curve of Bacteria
- Instruments used in Microbiology Laboratory
- McFarland Standards
- Monochrome Staining
- Negative Staining
- Preparation and Sterilization of culture media
- Serial Dilution in Microbiology
- Spread Plate Technique
- Streak Plate Technique