Practicals/Techniques

Question 1

What is MacConkey MAC agar used to test for?

what do lactose producing/fermenting bacteria do?

what do the bile salts in MAC do?

what are the different pH indicators?

Answer 1

gram negative bacteria

make acidic environment = pink, which can cause bile salts to precipitate out of MAC to balance pH

inhibit growth of gram positive organisms- left with gram negative on plate

neutral = red
<6.8 = pink
>6.8 = colourless

Question 2

What is the Gregersen test?

what is a positive & negative test?

Catalase test?

positive & neg test?

oxidase test?

pos? neg?

Answer 2

ability for bacteria to be lysed with potassium hydroxide - gram

positive = gram negative bacteria have materials spill = sticky suspension
negative = not sticky (gram +)

seeing which bacteria expresses higher levels of catalase

positive = bubbles (gram +ve) express more catalase
negative = no bubbles (gram -ve)

seeing if oxidase is present

positive = purple spot (gram +ve) expressed oxidase
negative = no spot (gram -ve)