Review Note

Last Update: 09/26/2023 05:06 AM

Current Deck: Testing Arthur::MGY377 Lec 1 + vid

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Front

Why is MacConkey Agar described as both selective and differential?

Back

Selective b/c bile salts and crystal violet inhibit the growth of Gram + bacteria so only E.coli and some Gram - can grow.

Differential b/c E.coli can ferment lactose but other enteric Gram - bacteria cannot. A colony of E. coli will change the pH due to fermentation, which turns the 'neutral red' dye pink.

Image

MacConkey Agar
MacConkey Agar is both 'selective'
and 'differential'.
It is selective because the bile salts
and crystal violet inhibit the growth
of Gram-positive bacteria. Only E.
coli and a few other Gram-negative
gut bacteria can grow on it.
It is differential because E. coli can
ferment lactose but other enteric
Gram-negative bacteria cannot. A
colony of E. coli will change the pH
due to fermentation. ..which turns
the 'neutral red' dye pink.
not E. coli
E. coli
eptone — 17 g
Proteose peptone — 3 g
Lactose — 10 g
Bile salts — 1.5 g
odium chloride —5 g
Neutral red — 0.03 g (the pH indicator)
rystal violet — 0.001 g
odium taurocholate (bile salts)
gar- 13.5 g
ater — add to make 1 litre• adjust pH to 7.1 +/— O.

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