labo exam 2

Question 1

MacConkey agar

Answer 1

inhibits growth of Gram +

lactose fermenters turn pink

Question 2

Mannitol salt agar

Answer 2

halotolerant, halophile

Mannitol fermenters turn the medium yellow

Question 3

starch agar

Answer 3

+ iodine, clear zone around colony= production of amylase

Question 4

milk agar

Answer 4

clear zone around colony= production of caseinase

Question 5

pheno Red-SUGAR- Durham tube

Answer 5

yellow gas= fermentation of the sugar (acid is produced)

Question 6

peptone iron agar

Answer 6

cysteine to H2S (turn balck, able to degrade cysteine and produce H2S)
complete reaction: cysteine= hydrogen sulfide (by cysteine disulfurase) = ferrous sulfide (black precipitate) by ferric ammonium citrate

Question 7

nitrate broth

Answer 7

+ nitrate 1,2: red: nitrate reducer
+ nitrate 1,2 + Zn: no reduction of nitrate
+ nitrate 1,2 + Zn: No change in color: complete reduction of nitrate to N2 (denitrifier)

Question 8

tryptone broth

Answer 8

+ Kovac’s reagent: red ring= indole producer from the AA tryptophan

Question 9

MR-VP (methyl red- Voges Proskauer)

Answer 9

MR: + methyl red, pink: acid production from glucose
VP: + VPI, VPII, pink = production of acetyl methyl carbinol

Question 10

simmons citrate agar

Answer 10

bright blue: organisms can use citrate as its sole carbon source

Question 11

what is IMViC tests

Answer 11

series of 4 tests that are used to differenciate memebers of the Gram - intestinal bacilli.
I= indole test (tryptone broth)
M= methyl red
V= voges-proskauer
C= citrate

Question 12

3 physical methods to control microorganisms + what they do

Answer 12

1. moist heat: coagulation or proteins thus rendering enzymes inactive ** it kill faster than dry heat
2. dry heat: oxidation of cell components
3. UV light: dimerization of thymine in the same strandof DNA which will cause errors in the DNA replication. Photoreactivation: exposure of the culture to visible light, it reverse the killing actions of UV light