Exp 7 E.coli detection

Question 1

E.Coli characteristics

Answer 1

Gram –

Short rod, no spores

Facultative

Ferments lactose to acid and gas

Metabolically capable = non-fastidious

Question 2

FDA method

Answer 2

Bacteriological Analytical Manual (BAM)

Question 3

BAM steps

Answer 3

Homogenate of 25 g in 225 mL of PBS

Enrichment step

Direct plate onto MacConkey agar (incubation 35 °C, 24h)

Hybridization with specific gene probes for virulence genes

Question 4

rapid method

Answer 4

LST-MUG assay

Question 5

LST-MUG assay

Answer 5

based on the presence of β-glucouronidase (GUD) in E.coli, which cleaves the MUG substrate to release 4-methylumbelliferone

Question 6

biochemical properties of E.coli

Answer 6

Indole (Tryptophan metabolism) +

Methyl Red (Acidity) +

Voges/Proskauer
(Butaindiol/acetoin metabolism) –

Citrate –

Sugar Fermentations

Eosin Methylene Blue

Question 7

Test for biochemical

Answer 7

IMViC

Question 8

IMViC

Answer 8

Indole, Methyl Red, Vogue-Proskauer, Citrate Utilization

Question 9

Indole test

Answer 9

Indole test is used to determine the ability of an organism to split amino acid tryptophan to form the compound indole. Tryptophan is hydrolyzed by tryptophanase to produce three possible end products – one of which is indole.

Question 10

Methyl Red test:

Answer 10

To determine if the medium become more acidic due to mixed acid production

Question 11

The Voges-Proskauer (VP) test:

Answer 11

presence of the neutral end-product acetoin

Question 12

Citrate test:

Answer 12

The principle of the Simmon’s citrate agar test is as follows. The enzyme citrate permease imports citrate in the cell. Inside the cell, the citrate is oxidized to yield the gas carbon dioxyde. When this gas is combined with sodium and sodium carbonate is formed, which changes the color of the agar.

Question 13

mixed acid fermentation acids

Answer 13

lactic acid, succinic acid, acetic acid

Question 14

number of moles during mixed fermentation

Answer 14

In mixed acid fermentation, E. coli produces per mol glucose (fill 4 mol acidic products,1 mol EtOH,1 mol CO2, and 1 mol H2.