Lab Practical

Question 1

What is magnification of ocular lens

Answer 1

10x

Question 2

Total magnification when using scanning
Low?
High power?
Oil?

Answer 2

4 x 10= 40x total
Low= 10 x 10= 100x
High= 40 x 10 = 400x
Oil= 100 x 10 = 1000x

Question 3

What is the condenser lens

Answer 3

Concentrates light on subject

Question 4

What is the iris diaphragm

Answer 4

Adjust amount of light admitted into condenser

Question 5

How much ml of sterile agar into a Petri dish

Answer 5

15ml

Question 6

Define a colony forming unit

Answer 6

Visible mass of microbial cells resulting from growth of one cell or clump of cells on medium

Question 7

Chromogenesis of cfus refer to what

Answer 7

Their pigmentation

Question 8

Cfu optical characteristics refer to

Answer 8

How opaque (not allowing light to pass!) or translucent (allowing light to pass) they are 
( or iridescent or opalescent or glistening or dull)

Question 9

3 descriptive terms for cfus

Answer 9

Pigmentation, optical characteristics, colony surface

Question 10

Difference between independent and dependent variable

Answer 10

You manipulate the independent variable (the change), measure the outcome of the dependent variable (variable affected by the change)
(Ex: amount of water given to plants: size of plants, health of plants)

Question 11

Briefly list how to do a wet mount slide

Answer 11

Drop of water on slide, add culture w transfer loop, mix, place cover slip over

Question 12

Which was more effective at removing germs from hands; hand washing or sanitizer

Answer 12

Washing

Question 13

How transfer loop and culture tubes are sterilized

Answer 13

Bactericinerator 10-15 sec

Question 14

Describe how to make a dry mount slide (smear)

Answer 14

Drop of water, make target circle, sterilize loop and transfer organisms, spread drop out, allow to dry on hot plate set to LO
once dry; dye w crystal violet, methylene blue, or carbolfuchsin, remove excess w stream of water, blot dry

Question 15

gram Positive v gram negative gram stain color

Answer 15

Positive= purple (crystal violet remains) 
Negative= pink (crystal violet washed away Bc pokes holes in thin peptidoglycan layer)

Question 16

Structural difference between gram neg and pos bacteria

Answer 16

Pos= thick peptidoglycan cell wall w teichoic acids 
Neg= outer lipid membrane, thin peptidoglycan layer

Question 17

How a negative stain works

Answer 17

Nigrosin dyes the background of the slide, cells appear clear and unstained
Little distortion in morphology

Question 18

Acid-fast v non-acid-fast colorization

Answer 18

Acid-fast= Red 
Non= blue (counterstained)

Question 19

Why acid-fast organisms retain the first dye, carbolfuschsin

Answer 19

Have waxy material in cell wall (mycobacterium), heat(mordant) applied when staining and waxy material absorbs dye

Question 20

Purpose of spore stain

Answer 20

Stain endospores (v resistant cell structure)

Question 21

Purpose of blotting paper in spore stain

Answer 21

Prevents rapid evaporation of stain (keep it saturated!)

Question 22

Spores of a spore stain appear what color, vegetative cells?

Answer 22

Green

Vegetative = Red

Question 23

Radiation in what region of light spectrum are lethal to microorganisms

Answer 23

Ultraviolet region; between 100-400 nm

Question 24

Most lethal UV wavelength on microorganisms

Range of effective germicidal activity

Answer 24

265 nm (optimal absorption by DNA) 
Germicidal= 240-300nm

Question 25

How UV radiation hurts microbes

Answer 25

Forms thymine dimers (mutates genetic code)

Question 26

Enzyme that fixes thymine dimers (photoreactivation)

Answer 26

Pyrimidine dimerase

Question 27

Which more resistant to UV light: serratia marcescens or bacillus subtilis
Why?

Answer 27

Bacillus subtilis more resistant Bc gram pos, thicker cell wall

Question 28

Goal of streak plate method

Answer 28

Isolate individual CFUs

Question 29

Procedure for streak plate

Answer 29

Flame loop, cover area 1
Flame again, cover 2 … etc
Flame between each streak !

Question 30

How to interpret fermentation test

Answer 30

Turns yellow: fermented the broth and lowered the pH (acid produced)
Bubble in Durham tube: produced gas (CO2)
(Acid or acid+gas= fermentation occurred)

Question 31

Purpose of hydrogen sulfide test

Answer 31

Metabolic by product of certain bacteria, v poisonous gas, if produced reacts w heavy-metal salt forming black precipitate

Question 32

How hydrogen sulfide test works

Answer 32

Peptone contains thiosulfate and sulfur containing amino acids, if bacteria can break down amino acid it combines w sulfur creating hydrogen sulfide gas

Question 33

Chemicals used for inhibiting bacterial growth are bacteriostatic or bactericidal

Answer 33

Bacteriostatic

Question 34

Purpose of coagulate test

Answer 34

Presence of coagulase enzyme indicates high pathogenicity (can wall itself off from host immune system)

Question 35

Neg v positive coagulase test

Answer 35

Evidence of clotting= positive, has coagulase ezyme that combined w platlets in rabid plasma

Question 36

Molds are usually anaerobic aerobic or facultative

Answer 36

Aerobic (need air to grow)

Question 37

Purpose of Vaseline in mold growth plate

Answer 37

Lifts cover slip up, exposes mold to air

Question 38

Requirements of growing mold cultures

Answer 38

O2, moisture