exp 5: determinatio of coliform in water by MPN Flashcards

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1
Q

what is the potability of water determinedby

A

the KINDS of microorgsnims not the number
as long as pathogens are not present

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2
Q

What does the public health service drinking eater standards state baout water

A

it should be entirely free of pathogens

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3
Q

how are pathogens introduce

A

fecal origins, seweage system

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4
Q

coliform bacteria used as an indicator why

A

bc sewages have alot of them, associated with fecal matter
-can be detected easier and quicker than pathogens
-presence indicates presence of fecal matter, not of harmful microorganisms as coliform are non-pathogenic

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5
Q

Sequence of most probably number method (MPN test)

A

1) Presumptive test
-innoculate known amount of water into lauryl tryptose tubes, if it contains gas after 48h, then it is PRESUMED to have fecal matter and unsafe to drink
2) Confirmed Test
-sometimes pos result of presumed may be due to the presence of other bacteria such as clostridium or bacillus so this test is done to ensure that it is coliform
-loopful from laural tryptose added to green lactose bile broth (more selective for coligorm)
-if gas, then pos
-OR can make a eosin methylene blue (EMB) or ENDO streak plate of laural broth (pos if GREEN METALLIC SHEEN typical coliform colonies or PINK colonies with dark center (E.aerogenes) is present
3)Completed Test
-innoculate the colonies from the confirmed test into Lauryl tryptose broth, checks to amke sure that acid/gas is produced)
-streak a nutrient agar slant using the same colony (slant used to do a gram test to see if it is gram-neg, nonsporeforming bacilli : COLIFORM)

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6
Q

what does coliform look like on endo or EMB plate (select for gram neg)

A

-GREEN METALLIC SHEEN (ecoli)
-PINK WITH DARK CENTER (e.aerogenes)

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7
Q

METHOD

A

PRESUMPTIVE
-3 double strength samples LAURYL
-6 single strength LAURL
-added creek water to it
-observe for gas

CONFIRMED TEST
add three loopfuls of lauryl to green lactose bile broth
-streak plate the highest diluted (one of the 0.1 ml single strength) on the plate

COMPLTETD
innoculate one laural tube and an agar slant
on slant make a gram stain and look to see if it is gram neg rods with no spores

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8
Q

What is the MOST PROBABLE NUMBER

A

-techniqie to coint the # of cells
-the most probable number of coliform present in the sample
-use the MPN index to determine
-essentailly just look at how many of the double strength adn how many of the single strength got pos results and match to it

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9
Q

Why can EMB be used for confirmed test

A

because it inhibits the growth of gram pos due to methylene blue
-gram neg LACTOSE FERMENTERS produce dark center colonies
-coliform, ecoli and enterbacter can be dofferenctiated on it based on how they look. ecoli have grreen shee n e aero does not

-select broth of the highest dilution (so one of the 0.1 ml ones) for test

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10
Q

why is ecoli a better indicator of sewage presence than enterbacter aerogenes

A

ecoli not normally found in soil whereas enterobacter is

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11
Q

what does ecoli look like on emb agar compared to e aerogenes

A

ECOLI: metallic green sheen, flat

E.Aerogenes: non metallic sheen, gummy, mucoid, larger

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12
Q

what was seen on the gram stain

A

PINK RODS

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13
Q

what were the results

A

MPN
presumptive: 4.6 coliform/ml
confirmed: 4.6 coligorm/ml

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