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why is agar used as solidifying agent in culture media instead of gelatin?

agar remains as a solid during growth of bacteria and few microbes can degrade agar

Heliobacter pylori bacteria grow in human stomach and produce large amounts of urease. Of what value is this urease to Heliobacter?

it neutralizes the very acidic environment of the stomach

Why is baby's wet diaper have smell of ammonia?

high amounts of urea or uric acid which are both sources of ammonia

What would you find in the liquid of hydrolyzed gelatin?

growth of bacteria

When an exoenzyme hydrolyzes gelatin

it liquifies and does not solidify even when cooled below 20 degrees C

how can organisms that do not use starch grow on a starch agar plate?

another organism on the starch agar plate breaks down the starch into smaller sugars

if an organism grown in th OF-glucose medium that is exposed to air, is the organism oxidative or fermentative? Explain.

oxidative. acids are produced as intermediates in respiration

how can you tell from OF-glucose medium whether an organism uses glucose aerobically?

it turns yellow in the top of the open tube

how can you tell from OF-glucose medium whether an organism ferments glucose?

it turns yellow

how can you tell from OF-glucose medium whether an organism does not use glucose?

it turns blue or green

How can you tell amylase is an exoenzyme and not an endoenzyme?

Exoenzyme is determined by looking for a change in the substrate outside of the bacterial colonies

The clearing around bacteria in a starch hydrolysis test indicates that the starch was ____________


In a starch hydrolysis test unchanged starch will stain____________

dark blue or black or dark brown

nutrient agar that contains vancomycin is selective/differential for _________________

selective; bacteria resistant to antibiotic vancomycin

what ingredient is what makes mannitol salt selective?


EMB agar is selective/differential


peptone is used as a __________ ___________ in media

food source

the purpose of agar in media is

to contain culture media

human cells would stain


Why would a physician perform a Gram stain on a sample before prescribing and antibiotic?

to determine treatment and what antibiotic to prescribe

Suppose you are viewing a gram-stained field of red rods an purple cocci through microscope. what would you conclude?

the sample is mixed bacteria

suppose you performed a gram-stain on a sample from pure culture for bacteria and observed a field of red and purple cocci. adjacent cells were not always the same color. what do you conclude?

it was a badstain

what are the steps of gram-staining procedure in order?

1. crystal violet 2. iodine 3. ethyl alcohol 4. salfranin (no step can be omitted)

Why will gram-positive cells more than 24 hours old will stain negative?

because the cell walls degrade and may not retain the primary stain

Bacteria can be seen without staining. Why then was Koch's recommendation for fixing and staining bacteria important in microbiology?

it makes it easier to see the bacteria

can dyes other than methane blue be used for direct staining?


In heat fixing bacteria, what would too much heat do to the cell?

damage the cell and you would not be able to see it through the microscope

methylene blue can be prepared as a basic stain or an acidic stain. how would the pH of the stain affect the staining of bacteria?

pH determines a particle charge. methylene blue is considered basic stain, if it is negative ion, it is an acidic stain

the purpose of heat fixing the smear is to...

kill the organism and help cells stick to slide and prevent cell lysis

another method of fixing smears is to use methanol instead of heat. Alcohol chemically fix the bacteria by...

removing water to dehydrate cell and it kills the cell

the value of a simple stain is to ...

determine cell morphology, size, and arrangement

the catalase test is used often used clinically to distinguish two genera of gram-positive cocci, _________________ and ________________; it is also used to distinguish genera of gram-positive rods ______________and _____________

staphylococci, streptococci; bacillus, clostridium

how can the pseudomonas aeruginosa grow in the absence of oxygen?

it is facultative

bacteria capable of living with or without oxygen

facultative anaerobes

bacteria that cannot tolerate the presence of oxygen because they lack catalase

obligate anaerobes

require oxygen

obligate aerobes

bacteria that cannot use bacteria but tolerate it fairly well

aerotolerant anaerobes

Aerobic bacteria can not grow in the absence of Oxygen. what would you need to determine whether bacteria growing on a petri plate from the brewer jar are aerobes?

gas envelope of sodium bicarbonate

in Thioglycolate tube, _________ appears in the presence of access oxygen, and _________ when it is reduced

pink; colorless

what do you attribute odors of anaerobic decomposition?

methane gas is produced

clostridium bacteria are killed in the presence of oxygen. would you expect it to produce catalas

No, because oxygen is not present

why would cytochrome oxidase deficiency cause sever muscle weakness?

cytochrome oxidase helps regulate energy production

nitrate reduction would occur more often in the presence or absence of oxygen? Why?

absence, because there is more energy where oxygen is

the presence of gas in nitrate test indicates

nitrates were reduced to nitrogen gas

anaerobic respiration and fermentation both do NOT require oxygen. what are differences

anaerobic respiration uses substance such as sulfate or nitrate, whereas fermentation uses same molecule as donator and acceptor (has no external electron acceptor)

hydrogen peroxide bubbles when poured on skin cut because

it is catalase and getting rid of infection

______ is final electron acceptor in aerobic respiration. ___________________________ acts as the final acceptor in anaerobic respiration

oxygen; inorganic compounds other than oxygen

how can you tell that the media provided for this exercise were sterile?

no growth present

for bacterium, what is the evolutionary advantage to forming pellicle in a liquid medium?

to access oxygen

aseptic technique is used to

exclude contaminates

how do you know bacteria in a semisolid agar deep are motile?

shows appearance of branching from the point of inoculation

_______________ is another way to determine motility


primary use of deeps

determine motility

primary use of broths

provide large number of bacteria in a small space and they are easily transported

inoculation loop is preferable for transferring bacteria into a

broth culture

inoculating needle is preferable fro transferring bacteria into an

agar deep

agar technique provides more info than broth because

one can see if there are different kinds of microbes by the size and shape of the colonies

the value of a petri plate in microbiology

they contain solid media and provide a large surface area for examination of colonies

bacteria use _____________ and _____________ for nutrient agar

peptone and beef extract

structural difference b/w capsule and slime layer

capsule is organized in tight matrix that excludes small particles; slime layers are more easily deformed and will not exclude particles and is more difficult to see

function of capsule

stick cells together and protects cells from digestive enzymes and chemicals

advantages of endospore formation confers upon a bacterialcell

helps dehydrate it and intercalates in DNA, which stabilizes DNA against heat denaturation

transient microbiota

microbes that are present for days or weeks

normal microbiota

microbes that are permanent

a surgeon washes hands with 10 minute scrub followed by antiseptic because

this removes transient microbiota

increased magnification affect field of vision how?

decrease field of vision, less of sample is seen


when a subject is in focus with one lens, it will be in focus with all the lenses

__________ affects the amt of light reaching the ocular lense


2 ways to enhance resolving power

numerical aperture, and smaller wavelengths of light

what are the advantages of low-power obj. over oil immersion obj for viewing fungi or algae

because fungi have large cells and low power allows for better depth of vision and can use lower light

if water were accidentilly used in place of immersion oil ...

the image would not be clear, because water doeas not have same refraction index as glass

source of energy for bacterial flagellar movement comes from the

proton motive force

function of bacterial flagella is

movement through liquid and to change direction of the cell

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