exp 6: determination of coliform by MEMBRANE

Question 1

what does the endo medium do

Answer 1

promote coliform growth while inhibiting the growth of other microorganisms
-in this it helps to isolate for the wanted microorganisms or at least limit microorganisms that would grow on our membrane filter since usuing RAW water would nomally just cause an overgrowth on the membrane

Question 2

What are coliform. bacteria able to break down

Answer 2

LACTOSE, break them down into ALDEHYDES

Question 3

Why is endo medium useful for coliform

Answer 3

contain lactose and a dye called FUCHSIN, which reacts with the aldehydes formed from the breaking down of lactose and makes a compledx which appears SHINY GREEN, therefore the green sheen colonies identify coliform since few other microorgs other than coliform can break down lactose

Question 4

What are the two types of coliform groups

Answer 4

1) Total Coliform
-ferment lactose and produce acid/gas within 48 hours, or form GREEN SHEEN colonies on membrane filters using endo broth (24h 37 degrees)

2) FECAL COLIFORM
-ferment lactose and produce acid/gas
-produce BLUE COLONIES ON membrane filters using m-FC broth

Question 5

Why must we differentiate between the two types of coliform

Answer 5

because coliform can be found from sources OTHER THAN FECAL MATTER so may not indicate contamination (PATHOGENS), so fecal coliform counts will be more indicative of fecal pollution by warem bloooded animals than total coliform counts

Question 6

Advantages and disadvantages of this membrane filter method compared to multiple tube test (MPN)

Answer 6

membrane filter has greater sensitivity since larger volume sof water can be tested
-easier to reproduce these results
-shorter time to do it because does not required completed or confirmed tests

DISADVANTAGE OF MEMRABE:
- water must be free of Cyanobacteria since this can clog up filter

Question 7

Method

Answer 7

add 100 ml of water to the filter with the grid thing on it

-after sample drawn through rinse with sterile water
PLACE CAREFULLY ON AGAR, make sure that grid side is up

repeat with other filter as well

Question 8

how to determine the numnber of coliform on each plate

Answer 8

the number of colonies (green for EMB, blue for MFC)

Question 9

how does mfc isolate for it

Answer 9

has bile salts that prevent the growth of call types of coliform