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Flashcards in Lab 9 Deck (10):
1

What is the definition of coliform bacteria?

Coliforms are Gram-negative bacilli (faculative anaerobes) that ferment lactose (milk sugar) producing acid and gas products.

2

What coliform species is generally used as an indicator of fecal water contamination?

E.coli

3

What media is used in the presumptive test?

The media used was double-strength phenol red lactose broth (PRLB)

4

What is the function of the phenol red?

its function is its a pH indicator.

5

What is the function of the Durham tube?

The function of the Durham tube is for trapping gas produced during bacterial growth.

6

How is a positive and negative presumptive test recognized?

Color change to yellow and presence of gas in the Durham tube is a positive test result. A negative presumptive test is recognized by no color change and no gas.

7

Explain the "why" of a positive test.

Color change to yellow and presence of gas in the Durham tube is a positive test result because coliforms can ferment lactose which produces acid, where we get our color change from pink to yellow because of pH change, and gas where we get our bubble in the Durham tube.

8

What media is used in the confirmed test?

The media used in the confirmed test was EMB eosin methylene blue.

9

What is the function of the eosin and methylene blue in the media?

The function of the eosin and methylene blue in the media is it produces distinct colonies, the dyes in the medium will cause lactose-fermenting bacteria to produce a purple/pink color, black center or metallic sheen. The dyes also inhibit the growth of Gram-positive organisms.

10

How is a positive confirmed coliform test and a negative test recognized?

A positive confirmed coliform test is recognized by looking for E. coli colonies appearing very dark and there is often a green metallic sheen around the colony when light is reflected. and E. aerogenes colonies which are typically larger, pink colonies with a dark center. Presence of colonies of either organism is a positive confirmed coliform test. A negative test does not have either colonies present.