Given below are two statements: Statement I: MacConkey agar is a media used for recovery of Gram positive bacteria from mixed bacterial culture.…
Given below are two statements:Statement I: MacConkey agar is a media used for recovery of Gram positive bacteria from mixed bacterial culture.Statement II: The bile salts and crystal violet in MacConkey agar inhibit growth of some bacteria.In the light of the above statements, choose the correct answer from the options given below:
Select an option to attempt
Correct Answer: Option D
Explanation
MacConkey agar selectivity:MacConkey agar is a SELECTIVE and DIFFERENTIAL medium:• Selective agents: Bile salts and crystal violet — these inhibit the growth of GRAM-POSITIVE bacteria (disrupting their less protective cell membranes).• Selective for: GRAM-NEGATIVE bacteria (enteric bacteria such as E. coli, Klebsiella, Salmonella, Shigella, etc.).• Differential: Lactose fermenters produce acid → pH indicator (neutral red) turns colonies PINK/RED. Non-fermenters remain colourless.Evaluation of statements:• Statement I: 'MacConkey agar is used for recovery of Gram-POSITIVE bacteria' — FALSE (it selects for Gram-NEGATIVE).• Statement II: 'Bile salts and crystal violet inhibit growth of some bacteria' — TRUE (they inhibit Gram-positive bacteria).Answer: Statement I is false but Statement II is true (Option 4).