·MacConkey Agar is both selective and differential
i. Selective:
Ø Contains bile salts and crystal violet
Ø Inhibits growth of gram-positive bacteria
Ø Isolates gram-negative bacteria
ii. Differential:
Ø Contains lactose and neutral red
Ø Lactose fermenters produce acid, causing the colonies to turn red
Ø Non-lactose fermenters do not produce acid. Thus, colonies either remain their normal colour or the colour of the medium
·Examples of selective and differential MacConkey agar:
i. Selective:
https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEifA_dd_12HTAv2_R10mgzL4Q-BRbnTNLSHvXmvRW-ezfe0LMwNwEhv4lGWSpGP0QsrRgZrXqp-XXhmEAvjRNJIzta4CNxI44panv99Ms9ygxegeKV1kHABQPfxh70IQjnds4KTm3DqP8p7/s1600-h/MacConkey_agar.jpg
Gram-positive bacteria- red colonies
Gram-negative bacteria- colourless colonies
ii. Differential:
https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhQ_TFHYc2h1h031cuzklhUDWXGlWEGXcZ3FpvnBAAaeUFw290eXTDNlhWZyBCHI2cDPZ3D8JxvukJxamjoBl3RUiINEUK54_Oiz7l6fSJtOHaI5W7sjPX6TYGc_NxC35iLreATAz6QIvjr/s1600-h/MacConkey_agar_with_LF_and_LF_colonies.jpg
Lactose fermenters turn the colonies pink.
Colonies of the non-lactose fermenters are colourless.
