MacConkey Agar w/ 0.5% Bile Salts w/o Crystal Violet

 Principle

• MacConkey agar is used for the identification and enumeration of lactose fermenting and lactose non-fermenting enteric bacteria. It is recommended by the BIS committee under the specifications IS 5887 (Part I and Part II) -1976.
• The media is composed of peptone, lactose, bile salt, sodium chloride, neutral red, and agar. Peptones provide nitrogen and other nutrients necessary for the growth of microorganisms.
• Lactose is a carbon source and plays an important role for the selection of lactose fermenting microbes. Bile salt inhibits the growth of gram-positive except Staphylococci and Enterococci. Neutral red is a pH indicator dye.
• Agar is the solidifying agent. When lactose is fermented, acid is produced and results in bile salt precipitation.  Since the lactose fermenting colonies of coliform bacteria are pink in color and may be surrounded by a zone of bile precipitation.
• While the bacteria that do not ferment lactose remain colorless. This medium is modified to permit the growth of Staphylococcus and Enterococcus. It lacks crystal violet which inhibits the growth of gram-positive bacteria. The Staphylococci produce pale pink to red colonies and Enterococci produce compact tiny red colonies.

 Use: Recommended for isolating and differentiating enteric microorganisms and permitting the growth of Staphylococci and Enterococci. It is also used for the identification and enumeration of lactose fermenting and lactose non-fermenting enteric bacteria. It is recommended by the BIS committee under the specifications IS 5887 (Part I and Part II) -1976.