microbiology lab final - text

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what is pink coloration due to in indole test?

tryptophanase and indole production. kovac's reagent (dmb/amyl alcohol/hcl) makes complex if there is free indole

what does amyl alcohol (part of the Kovac's reagent) do in the indole test?

allows the complex to float on top of the medium

halo around the optochin disc indicates which bacteria?

streptococcus pneumonia

halo around the bacitracin disc indicates which bacteria?

streptococcus pyogenes

mannitol salt agar is used to isolate and differentiate which two bacteria?

pathogenic staphylococcus aureus and non pathogenic staphylococcus epidermidis

why are pathogenic strains of s. aureus able to ferment mannitol sugar and change color around bacteria to a yellow halo

the mannitol fermentation and acid fermentation does this. the pH is lowered and changes the color to yellow

what is the indole enriched with?

tryptophan from the peptic digest of casein

what is the enzyme the indole test is looking for?

tryptophanase enzyme, which is secreted by some bacteria

what does the addition of the kovac's reagent do in the indole test?

it forms a red/pink colored complex that floats on top of the media, this is a positive result

what is the citrate test used to differentiate?

differentiate between common intestinal bacteria

what are the two enzymes needed to have a citrate positive result

citrate permease (helps bring citrate into cell) and citrase (breaks down citrate once inside of cell)

what is the original color of the simmons citrate media

green, if a positive result the medium will turn blue. e aerogenes is blue and e. coli is green

what is the methyl red test used for

used to detect if bacteria are able to form stable mixed acids by the fermentative pathway. used to differentiate primarily between bacteria that produce large amounts of acids from those that generate acetone/butanediol. the methyl red is the pH indicator, red at pH 4.4 turns yellow when pH goes towards alkaline pH 6.0, orange shade is inconclusive result.

what does the voges-proskauer test look for

it is used to check if acid products are further metabolized to form butanediol via the butanediol pathway. butanediol is non acidic.

is the detection of butanediol in the voges-proskauer test easy or difficult

it is difficult to detect the presence of butanediol. instead the two reagents (vp-I alpha napthol and vp-II KOH) react with each other to form a colorless complex. this complex reacts with the peptones in the media and forms red/wine colored complex. it is easier to check for acetoin than butanediol, acetoin comes before butanediol in the pathway. if there is no color change or it is copper color then it is VP negative

what does macconkey agar test for?

intestinal fermenters from non fermenters

describe the contents of macconkey agar

bile saltes, lactose sugar, crystal violet, ph indicator

what do the bile salts in macconkey agar do?

they inhibit the growth of all but certain gram negative rods

what does the lactose sugar do in macconkey agar?

it shows with bacteria are able to ferment lactose sugar. the ph indicator then is affected by the acid production of the fermentation and changes color, the lower the ph the pinker the colonies will be

what are the two color results for the macconkey agar test?

pink colonies: means they can ferment lactose and produce acid to change the ph indicator. yellow/colorless colonies, they do not use lactose. instead they metabolize the peptone components of the media and ammonia is generated and it pushes the pH into alkaline

what is the purpose of the urea broth test

to find out which bacteria are rapid urease producers

name one rapid urease producer

proteus mirabilis

nutrient agar, what do you see happening to pseudomonas sps

the green color and mucoidal colonies. the green is because of the phycocyanin pigment. happens on burn victims because pseudomonas is a ubiquitous bacteria

mannitol salt agar test, what is it used for?

to isolate and differentiate pathogenic s. aureus from non-pathogenic s. epidermidis

blood agar test, what is it used for?

to isolate streptococcus pneumonia from streptococcus pyogenes.

what are the three types of hemolysis

alpha (partially uses RBC producing a discoloration); beta (completely uses rbc producing a clear zone); gamma (does not use rbc and no change in medium is seen)

example of alpha hemolysis

streptococcus pneumoniae

example of beta hemolysis

streptococcus pyogenes

describe the nutrient agar colonies for s epidermidis and s aureus

s epidermidis have less growth, whiter and brighter, pin head colonies, non pathogenic.
s. aureus has more growth, off white/buttery color, large colonies, pathogenic

what are the two stages of the life cycle of the protozoa?

trophozoite and cyst

what are vacuoles in terms of protozoa?

conspicuous organelle seen in some members. 2 types contractile vacuole; food vacuole

describe contractile vacuole

regulates fluid within the cell, avoids cell bursting

describe food vacuole

membranous sac formed by the plasma membrane, fuses with the lysosomes inside the cell. lysosomes are the food vesicles, they digest the food stuffs to allow for absorption

what are cysts?

they are the resting form with dormant cytoplasm. is a means of survival and dispersal to new host. are the equivalent of endospores but are not resistant to heat and other environmental conditions

what does the micronuclei control?

it is required for sexual reproduction

what does the macronuclei control?

it is derived from the micronuclei. it has a role in routine cellular functions and asexual reproduction

what is the ectoplasm of protozoan cell

it is slightly more dense, granular, and just below the plasma membrane

what is the endoplasm of protozoan cell

beneath the ectoplasm, there is no barrier between the two.

what is the mode of action for bacitracin?

it inhibits transport of peptidoglycan precursors, NAG/NAM across the membrane. it is toxic and restricted to topical application, it is generally part of first aid ointment.

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