Lab Practical Flashcards
What is magnification of ocular lens
10x
Total magnification when using scanning
Low?
High power?
Oil?
4 x 10= 40x total
Low= 10 x 10= 100x
High= 40 x 10 = 400x
Oil= 100 x 10 = 1000x
What is the condenser lens
Concentrates light on subject
What is the iris diaphragm
Adjust amount of light admitted into condenser
How much ml of sterile agar into a Petri dish
15ml
Define a colony forming unit
Visible mass of microbial cells resulting from growth of one cell or clump of cells on medium
Chromogenesis of cfus refer to what
Their pigmentation
Cfu optical characteristics refer to
How opaque (not allowing light to pass!) or translucent (allowing light to pass) they are ( or iridescent or opalescent or glistening or dull)
3 descriptive terms for cfus
Pigmentation, optical characteristics, colony surface
Difference between independent and dependent variable
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)
Briefly list how to do a wet mount slide
Drop of water on slide, add culture w transfer loop, mix, place cover slip over
Which was more effective at removing germs from hands; hand washing or sanitizer
Washing
How transfer loop and culture tubes are sterilized
Bactericinerator 10-15 sec
Describe how to make a dry mount slide (smear)
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
gram Positive v gram negative gram stain color
Positive= purple (crystal violet remains) Negative= pink (crystal violet washed away Bc pokes holes in thin peptidoglycan layer)
Structural difference between gram neg and pos bacteria
Pos= thick peptidoglycan cell wall w teichoic acids Neg= outer lipid membrane, thin peptidoglycan layer
How a negative stain works
Nigrosin dyes the background of the slide, cells appear clear and unstained
Little distortion in morphology
Acid-fast v non-acid-fast colorization
Acid-fast= Red Non= blue (counterstained)
Why acid-fast organisms retain the first dye, carbolfuschsin
Have waxy material in cell wall (mycobacterium), heat(mordant) applied when staining and waxy material absorbs dye
Purpose of spore stain
Stain endospores (v resistant cell structure)
Purpose of blotting paper in spore stain
Prevents rapid evaporation of stain (keep it saturated!)
Spores of a spore stain appear what color, vegetative cells?
Green
Vegetative = Red
Radiation in what region of light spectrum are lethal to microorganisms
Ultraviolet region; between 100-400 nm
Most lethal UV wavelength on microorganisms
Range of effective germicidal activity
265 nm (optimal absorption by DNA) Germicidal= 240-300nm
How UV radiation hurts microbes
Forms thymine dimers (mutates genetic code)
Enzyme that fixes thymine dimers (photoreactivation)
Pyrimidine dimerase
Which more resistant to UV light: serratia marcescens or bacillus subtilis
Why?
Bacillus subtilis more resistant Bc gram pos, thicker cell wall
Goal of streak plate method
Isolate individual CFUs
Procedure for streak plate
Flame loop, cover area 1
Flame again, cover 2 … etc
Flame between each streak !
How to interpret fermentation test
Turns yellow: fermented the broth and lowered the pH (acid produced)
Bubble in Durham tube: produced gas (CO2)
(Acid or acid+gas= fermentation occurred)
Purpose of hydrogen sulfide test
Metabolic by product of certain bacteria, v poisonous gas, if produced reacts w heavy-metal salt forming black precipitate
How hydrogen sulfide test works
Peptone contains thiosulfate and sulfur containing amino acids, if bacteria can break down amino acid it combines w sulfur creating hydrogen sulfide gas
Chemicals used for inhibiting bacterial growth are bacteriostatic or bactericidal
Bacteriostatic
Purpose of coagulate test
Presence of coagulase enzyme indicates high pathogenicity (can wall itself off from host immune system)
Neg v positive coagulase test
Evidence of clotting= positive, has coagulase ezyme that combined w platlets in rabid plasma
Molds are usually anaerobic aerobic or facultative
Aerobic (need air to grow)
Purpose of Vaseline in mold growth plate
Lifts cover slip up, exposes mold to air
Requirements of growing mold cultures
O2, moisture
