Lab Questions

Question 1

MacConkey Agar

Answer 1

selective medium designed to indicate gram negative bacteria (enteric- in intestines) based on ability to ferment lactose. Bile salts and crystal violet inhibit growth of gram positive. Lactose fermenters turn pink!

Question 2

Enterobacteriaceae

Answer 2

gram negative bacteria that are capable of fermenting sugars such as lactose

Question 3

what plate can detect enterobacteriaceae bacteria?

Answer 3

MacConkey Agar

Question 4

Mannitol Salt Agar

Answer 4

selective for Halophiles ( thrive in high salt concentrations) and halo tolerant. Plate contains high level of salt (NaCl), the sugar mannitol and a pH indicator phenol red. if organism can ferment the mannitol the indicator turns yellow

Question 5

Starch agar

Answer 5

to detect starch hydrolysis or organisms- if capable of breaking down starch through amylase production will produce a clear zone around the plate while the rest of the plate is blue ( iodine wash)

Question 6

Milk agar

Answer 6

clear zone around the colony = production of caseinase that hydrolyzes casein

Question 7

Phenol red- SUGAR- Durham tube

Answer 7

phenol red indicator- turns yellow in acid enviromet ( below 6.8)
if organism can ferment the sugar an acidic byproduct forms (acetate?) = yellow

gas may form a bubble

Question 8

Peptone iron agar

Answer 8

to detect hydrogen sulfide production by microorganisms. cysteine —> H2s ( turns black bc able to degrade cysteine and produce H2S)

Question 9

nitrate broth

Answer 9

ability of an organism to reduce nitrate (NO3) to nitrite (NO2) using nitrate reductase and to use nitrification to produce N2 gas.

Question 10

first step of nitrate reduction test

Answer 10

add sulfanilic acid and napthylamine- if red occurs it means nitrate has been reduced to nitrite (positive result )

if not need to see if nitrate was not reduced or if nitrite has been fully turned into gas

Question 11

second step of nitrate reduction test

Answer 11

add powdered zinc- if turns red it means nitrate was present ! ( negative result ) and not reduced at all

Question 12

if after the addition of zinc the colour does not turn red this means

Answer 12

positive result and that the nitrate has been reduced into nitrogen gas

Question 13

if a red colour results after the addition of zinc it indicates

Answer 13

a negative result and that nitrate was still present

Question 14

if a red colour results after the addition of sulfanilic acid and napthylamine in the nitrogen broth test it indicates a

Answer 14

positive result and means that the nitrate (NO3) was reduced into nitrite (NO2)

Question 15

tryptone broth

Answer 15

ability to slit the amino acid tryptophan into indole

a positive test result in a red ring = indole producer

Question 16

MR-VP ( methyl red - Voges Proskaueh) test

Answer 16

test used to identify mixed acid fermenting bacteria that yield end acid product= RED from methyl red

AND

identify bacteria capable of producing acetyl methyl carbonyl from pyruvic acid (followed fermentation of glucose )

Question 17

Add MR - positive result is

Answer 17

red= acid production from glucose

Question 18

add VP1 and VP2 and a positive result is

Answer 18

red ring at top of broth tube= production of acetyl methyl carbonyl

Question 19

Simmons citrate agar ( in test tubes )

Answer 19

test used to determine the ability of bacteria to use citrate as its sole carbon source. if bright blue= organism used citrate as its sole carbon source

Question 20

IMViC test - what do the letters stand for?

Answer 20

acronym that stands for each of the four tests. first test is typtone broth (indole test ), MR-VP and then citrate 
I= indole
M= methyl red
V= Voges-Proskauer
C= citrate

Question 21

citrate positive test

Answer 21

bright blue= organism used citrate as its sole carbon source

Question 22

citrate test negative

Answer 22

green colour = no colour change

Question 23

what happens when UV light was exposed to microorganisms

Answer 23

damages DNA! UV light kills organisms in about 10 seconds. This is done by dimerization of thymine in the DNA- which disrupts the strand- can’t be copied.

Question 24

what happens during photo reactivation

Answer 24

the thymine dimer is broken ( by exposure to wave of longer wavelength)