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
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 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
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
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 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
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
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
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
for bacterium, what is the evolutionary advantage to forming pellicle in a liquid medium?
to access oxygen
how do you know bacteria in a semisolid agar deep are motile?
shows appearance of branching from the point of inoculation
primary use of broths
provide large number of bacteria in a small space and they are easily transported
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
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
advantages of endospore formation confers upon a bacterialcell
helps dehydrate it and intercalates in DNA, which stabilizes DNA against heat denaturation
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
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