Lab Practical 2

Question 1

what are the possible end products that you get from fermentation

Answer 1

acid
alcohol
gas–> never produced by itself, always with acid or alcohol

Question 2

fermentation: what does it look like when you have a positive result for acid

Answer 2

ph becomes acidic, detected by phenol red

red at neutral ph and turns yellow as becomes acidic

Question 3

fermentation: what does it look like whne you have a positive result for gas

Answer 3

tested in durham tube, if positive a bubble will form and the color will change

Question 4

fermentation: what does it look like when you have a positive result for alcohol

Answer 4

the only way to tell if there is alcohol is if there is no acid produced, but there is gas produced

Question 5

steps for fermentation experiment

Answer 5

E. coli, A. faecalis, S. pastorianus and 3 broth tubes consisting of lactose, glucose and sucrose.
transfer E. coli into glucose, sucrose, and lactose tubes
repeat for S. pastorianus and A. faecalis

Question 6

reactions of catalase activity

Answer 6

2h2o2–>(catalase) 2h2o + o2(bubbles)

Question 7

what can catalase differentiate between

Answer 7

enterococcus and staphylococcus

Question 8

what is the purpose of oxidase test

Answer 8

determine between obligate aerobe (+) and facultative anaerobe (-)
determine if the organism can produce oxidase

Question 9

what does a positive oxidase test look like

Answer 9

purple or pinkish color=obligate aerobe

Question 10

steps for oxidase test

Answer 10

1. oxidase test paper, wooden stick, oxidase reagent, e. coli, a. faecalis, p. aeruginosa
2. add a drop of reagent to paper
3. using wooden stick, transfer large amount of bacteria onto paper
4. the result should occur within 20-30 seconds

Question 11

nitrate reduction

Answer 11

no3–> no2–>nh3 or n2
reduced by nitrate/nitrite reductase
identify bacteria containing nitrate reductase

Question 12

positive nitrate reduction test

Answer 12

1. red color change = positive for nitrate reductase

2. no change= positive for nitrate reductase

Question 13

steps of nitrate reduction

Answer 13

1. e. coli, s. epidermis, p. aeruginosa, and 3 nitrate broth tubes
2. transfer bacteria into each tube
3. incubate fore 48 hours
4. add nitrate a and b reagents
   if red=positive for nitrate reductase
   if no change move to 2
5. add zinc
   if red=negative
   if no change=positive for nitrate reductase

Question 14

what is the purpose of the durham tube in the carbohydrate fermentation broth

Answer 14

it can detect gas produced by a fermentation pathway

Question 15

would an obligate anaerobe be positive for catalase? why?

Answer 15

no because they die in the presence of oxygen

Question 16

what end product reacts with nitrate A and nitrate B reagents

Answer 16

NO2 because NO3 has been reduced

Question 17

what is the function of zinc in the nitrate reduction test

Answer 17

reduce NO3 to NO2. if there is a color change the result is negative because there was NO3 still in there

Question 18

starch hydrolysis

Answer 18

starch can be used for food by some bacteria however it is too big to get through the membrane. some bacteria produce an exoenzyme called alpha-amylase which breaks down starch allowing it to get into the membrane and used for food
test if alpha amylase is produced

Question 19

starch hydrolysis reaction equation

Answer 19

starch–>(alpha amylase) dextrins, maltose, glucose

Question 20

positive result of starch hydrolysis

Answer 20

clear around black line

black line indicates starch, clear indicates alpha amylase

Question 21

steps of starch hydrolysis

Answer 21

1. streak bacteria in straight line on plate

2. incubate for 24 hours then observe

Question 22

casein hydrolysis

Answer 22

protease reduces casein to amino acid to use as a source of food for bacteria

Question 23

positive casein hydrolysis test

Answer 23

bacteria will be clear against the opaque milky agar plate

indicates presence of protease

Question 24

gelatin hydrolysis

Answer 24

gelatin is broken down by gelatinase into amino acids to be used as a food source.

Question 25

why is gelatinase a virulence factor

Answer 25

because it breaks down connective tissue bc gelatin is connective tissue

Question 26

steps for gelatin hydrolysis

Answer 26

get gelatin tubes, stab 3/4th of the way down with needle with bacteria, incubate for 48 hours, then place in fridge

Question 27

positive gelatinase test

Answer 27

liquid after fridge = positive | solid=negative

Question 28

DNase test

Answer 28

DNase breaks down DNA into nucleic acid to transport across membrane as a food source

Question 29

positive DNase test

Answer 29

clear is positive | stays teal, negative

Question 30

why is DNase considered a virulence factor?

Answer 30

because it can degrade host DNA

Question 31

why are some bacteria able to grow on a milk plate even though they do not hydrolyze casein

Answer 31

they are able to metabolize other nutrients

Question 32

2 benefits of gelatinase produced by bacteria

Answer 32

1. breaks down gelatin to be used as food | 2. virulence factor bc breaks down connective tissue

Question 33

what 3 tesets are preformed with the sim tube

Answer 33

sulfide, indole, motility

Question 34

hydrogen sulfide test determines

Answer 34

if the microorganism can produce h2s

Question 35

sulfide test equationss

Answer 35

cysteine --cysteine desulfurase--> pyruvic acid + ammonia + h2s or thiosulfate--thiosulfate reductase--> sulfite h2s (anaerobic respiration)

Question 36

positive sulfide test

Answer 36

dark black line through the middle

Question 37

indole test determines

Answer 37

if indole is produced

Question 38

indole equation

Answer 38

tryptophan--tryptophanase--> pyruvic acid + ammonia + indole

Question 39

positive indole test

Answer 39

bright red on top is positive

Question 40

motility positive test

Answer 40

black strays away from line = positive | straight line = negative

Question 41

what does IMViC stand for

Answer 41

Indole, methyl red, voges-proskeur, citrate

Question 42

methyl red/ voges proskeur determines

Answer 42

if it is a mixed acid ferementer or butandediol fermenter

Question 43

methyl red tests will be positive if

Answer 43

its a mixed acid fermenter and turns red, at a ph of 4

Question 44

methyl red will be negative if

Answer 44

its a butanediol fermenter and turns yellow, ph of 6

Question 45

voges proskeur test will be positive if

Answer 45

its a butanediol fermenter and there is a red color

Question 46

voges proskeur will be negative if

Answer 46

its mixed acid fermeneter and there is an absence of red

Question 47

MRVP test steps

Answer 47

use mrvp broth tubes and an innoculating loop | place bacteria in tubes, incubate and observe

Question 48

citrate test determines if

Answer 48

microorganisms can use citrate as their sole carbon source

Question 49

citrate equation reaction

Answer 49

sodium citrate--citrate permease/citrase--> pyruvic acid = oxaloacetic acid = co2

Question 50

positive citrate test

Answer 50

blue

Question 51

steps for citrate test

Answer 51

use slant tube, transfer bacteria by smearing

Question 52

urease equation

Answer 52

urea + water --urease--> co2 + ammonia + water

Question 53

urease test determines

Answer 53

if produce urease enabling bacteria to use urea as a source of nitrogen

Question 54

positive urease test

Answer 54

bright red

Question 55

urea test steps

Answer 55

transfer bacteria and incubate. if turns red produces urease