Practical 3 MacConkey & Eosin Methylene Blue

Question 1

define enterobacteriaceae

Answer 1

family of gram neg bacteria
the enteric “gut” bacteria

Question 2

define coliform

Answer 2

suggest fecal contamintation and the possible presence of enteric pathogens

Question 3

what are EMB and MAC agar selective for

Answer 3

these are selective for gram negative organisms

Question 4

why do EMB and MAC contain indicators

Answer 4

to differentiate lactose fermentors from non-fermentors

Question 5

what carbohydrate is contained in both EMB and MAC agar

Answer 5

lactose monohydrate

Question 6

What is the INHIBITOR for MAC agar

Answer 6

bile salts and crystal violet

Question 7

what is the INDICATOR for MAC

Answer 7

neutral red dye

Question 8

what do you tell a difference in a fermenter and non fermenter of lactose on MAC agar

Answer 8

fermenter- lower ph which turns colonies to pink/red
nonfermenter- retain their normal colors or color of broth

Question 9

in EMB agar what inhibits the growth of gram-positive organisms

Answer 9

Eosin Y & Methane Blue

Question 10

what is the INDICATOR in EMB agar

Answer 10

Eosin y & methane blue

Question 11

what color would indicate lactose or sucrose fermentation on EMB

Answer 11

Dark purple or black
pink to dark purple

Question 12

what color would indicate non fermenters of lactose or sucrose on EMB

Answer 12

typically retaining their normal color or take on the color of the media

Question 13

is EMB selective or differential

Answer 13

BOTH

Question 14

is MAC selective or differential

Answer 14

BOTH