lab test #3

Created by niquot 

Upgrade to
remove ads

117 terms

If a bacteria produces acid from carbohydrate fermentation, what color will the medium turn?


what substances do you drop onto the bacterial colony when doing the catalase production test

hydrogen peroxide

in the catalase production test, what enzyme catalyzes the reaction


how can you tell if a catalase production test is positive

bubbles form

what are the two enzymes involved in nitrate reduction

nitrate reductase and reductase

If both steps of nitrate reduction are complete, what is the final end product that is made.

ammonia or nitrogen

If you added drops of reagent A and reagent B in the nitrate reduction test and the medium turns red, what does that indicate about the chemical reaction?

nitrite is present in the medium, the bacteria was able to reduce nitrate to nitrite.

you are performing the nitrate reduction test. After adding reagents (A and B) to the medium, there is no change to the medium. What is the next step you take to find out if the nitrate was reduced

add zinc powder

You are performing the nitrate reduction test. If after adding zinc powder, the solution turns red. What does that tell you about the chemical reaction.

nitrate was present. therefore no nitrate reduction occurred.

In what type of medium does motility test take place.

semi solid medium with reduced amount of agar.

when testing for starch hydrolysis, what reagent is used on the starch agar plate?

Grams iodine

when start is combined with grams iodine, what color does it turn.

bluish black

When performing the starch hydrolysis test, what will the medium look like if the bacteria breaks down the starch?

Clear area in the medium around the growth.

in casein hydrolysis, the enzyme casease breaks down casein into what?

polypeptides and amino acids

what does a medium look like in which casein hydrolysis has occurred.

clear area around growth.

in gelatin hydrolysis the enzyme gelatinase breaks down gelatin into what.

polypeptides and amino acids.

you are performing the gelatin hydrolysis test. After inoculation, incubation and refridgeration . How can you tell if the bacteria has the enzyme gelatinase (and can breakdown gelatin).

the medium is liquid.

you are performing the urea digestion test (urea hydrolysis test). What color does the solution turn if the bacteria is able to complete urea digestion.

bright pink

when a bacteria digests urea, what bi-products are produced.

h2O,CO2, ammonia

if a bacteria has the enzyme cysteine desulfurase it can convert cysteine into H2S(hydrogen sulfide). What will you see in the medium if this happens.

a black precipitate.

ampicillin and vancomycin do what?

inhibit cell wall synthesis

levoflaxin does what?

blocks dna gyrase

erythromycin does what

interrupts protein synthesis.

which kirby bauer test result should be most effective in treatment


what ways do microorganisms acquire resistance

alteration, degradation, impermeability of antibiotics. or modification of metabolic pathway so inhibited enzyme is no longer needed.

antibiotics that are effect against a broad array of bacteria. including both gram(+) and gram(-) organisms?

broad spectrum

antibiotics that are effective against a limited range of organisms

narrow spectrum

you have the measure the zone of inhibition and look up the interpretive criteria to determine if the bacteria is susceptible(S), Intermediate(I), resistant(R). True or false?


zone size alone doesn't determine the bacterias susceptibility or resistance to the antibiotic. True or false


you should stop taking antibiotics when the symptoms go away, and you start feeling better. true or false


antibiotics are not effective vs viral illnesses true or false.



pathogen with that zone size will likely be killed/inhibited by the concentration of drug in the bloodstream provided by the usual dose of that agent


provides a buffer zone to prevent small differences in the test from having a major impact on the interpretation.


Pathogen with that zone size will not likely be killed/inhibited.

what is true of enteric bacteria?

they normally inhabit the digestive tract.
they are gram negative rods
they are facultative anaerobes
they ferment glucose

what is true of MacConkeys agar

Bacteria that ferment lactose look pink
it is selective for gram negative bacteria
it is differential

you inoculate MacConkeys agar medium with bacteria. the bacteria grows but does not turn pink. what do you know about this bacteria?

it is gram negative
it does not ferment lactose

how does triple sugar iron agar differentiate bacteria

some bacteria might produce gas, others won't
some bacteria might produce hydrogen sulfide, others won't
it differentiates bacteria based on the ability to ferment glucose and other sugars.

indole test

determines whether a bacteria can degrade thryptophan

methyl red test

tests for mixed acid fermentation and the ability of an organism to produce highly acidic end products.

voges-proskauer test

determines whether an organism produces acetion by fermenting glucose

citrate utilization test

determines whether an organism can utilize citrate as its only source of carbon

what would you be able to learn form an organism during the citrate utilization test

whether or not the bacteria produces alkaline end products
whether or not the bacteria can utilize citrate as its only source of carbon

MacConkey agar contains

contains crystal violet and bile salts

triple sugar iron (TSI) agar contains


Voges-proskauer test

Requires adding two reagents to the medium and shaking it.

Indole production

Contains tryptophan

triple sugar iron agar positive and negative results

medium turns black if the bacteria uses iron to produce hydrogen sulfide

indole production positive and negative results

if an organism can degrade tryptophan, a red ring appears at the top of the medium

methyl red test positive and negative results

an organism that doesn't produce acid will cause this liquid medium to remain yellow.

MacConkey agar selects for?

gram negative bacteria

Voges-Proskauer test mediums turns

reddish-pink color of acetoin is present

urea hydrolysis broth appears

pale or amber color in a negative test

citrate utilization test medium turns

blue blue indicating that a medium is alkaline

Enteric bacteria are

Bacteria that normally inhabit the human digestive tract

what enzyme breaks down starch into glucose?


MacConkeys agar is selective to what bacteria

Gram-negative bacteria

MacConkeys agar is a differential agar. True or False


A positive test for a MacConkeys agar test would be?

Bacterial growth is pink

What does an Indole test determine

Determines whether an organism can degrade tryptophan

In a urea digestion Ammonia will?

Raise the Ph

Casease breaks down milk protein which releases what?

amino acids

selective media

allow certain bacteria to grow while preventing other bacteria from growing.

differential media

contain indicators that distinguish bacteria from another

enriched media

contain extra nutrients, growth stimulants.

what is blood agar

both enriched and differential

blood agar is differential because types of bacteria lyse red blood cells similarly. true or false


what organisms does MacConkey agar inhibit

Gram positive bacteria

MacConkey agar is selective because it contains bile salts and crystal violet. true or false


what color will growth on MacConkey agar turn if a bacteria produces acid?


what is true of mannitol salt agar

it is selective
it has a Ph indicator
it is differential

Carbohydrate fermentation(broth)-what is the reaction?

(glucose,lactose,sucrose)------Fermentation/enzymes--------->acid & or gas

Carbohydrate fermentation(broth)-what is the procedure

Durham tube to detect gas formation Phenol red pH indicator is in the medium

Carbohydrate fermentation(broth)-what is the interpretation

red=no acid(-)
no gas(-)

Oxidase test(trypticase soy agar(TSA) plate-streak for isolation-reaction


Oxidase test(trypticase soy agar(TSA) plate-streak for isolation- what is the procedure?

smear bacterial colony onto drop of oxidase test reagent on filter paper

Oxidase test(trypticase soy agar(TSA) plate-streak for isolation- Interpretation

(+)-purple color within 1 mins
(-)-No purple(or delayed faint purple color)

Catalase production(trypticase soy agar(TSA) plate-streak for isolation- What is reaction

Hydrogen peroxide--->catalase--->2h2O + O2

trypticase soy agar(TSA) plate-streak for isolation- Procedure

Smear bacterial colnoy on glass slide; add drop of 3% hydrogen peroxide

trypticase soy agar(TSA) plate-streak for isolation- interpretation


Nitrate reduction(nitrate broth)-reaction

Nitrate--->nitrate reductase---nitrite---->reductase--->ammonia or nitrate

trypticase soy agar(TSA) plate-streak for isolation- Procedure

Stage 1- add 5 drops of (A sulfanilic acid) and (B napthylamine)
Stage 2- add C zinc powder

Motility test(motility test broth)-procedure

inoculate by stabbing with a needle

motility test(motility test broth)-interpretation

(+)organisms grow & spread away from line of innoculation
(-)Nonmotile will only grow at line of penetration

Indole production(Tryptophan broth)-Reaction

Tryptophan--->tryptophanase--->indole + pyruvate

Indole prodction(tryptophan borth)-procedure

Add 8 drops of Kovacs reagent

Indole production(tryptophan broth)-Interpretation

Red at top=indole present(+)
Yellow clean ring=no indole present(-)

Methyl Red Test(MRVP medium)-Reaction

Glucose---fermentation/enzymes-->highly acidic products

Methyl Red Test(MRVP medium)-Procedure

Add 5 drops methyl red indicator

Methyl Red Test(MRVP)-Interpretation

Red=acid is present
yellow=not acidic

Voges-proskauer test (MRVP medium)-reaction


Voges-proskauer test (MRVP medium)-procedure

Add 15 drops of VP reagent A;mix. Add 5 drops VP reagent B; Mix let set ~4hr

Voges-proskauer test (MRVP medium)-interpretation

Redish color in 4 hr(+)
Yellow brown-no acid(-)

Citrate utilization(citrate agar slant)-reaction


Citrate utilization(citrate agar slant)-procedure

Bromthymol blue pH indicator is in the medium

Citrate utilization(citrate agar slant)-interpration

blue=alkayline, citrate used(+)
green=not alkaline, citrate not used(-)

Carbohydrate fermentation(glucose,lactose,sucrose)-(triple Sugar Iron Agar(TSI))-Reaction


Carbohydrate fermentation(glucose,lactose,sucrose)-(triple Sugar Iron Agar(TSI))-Procedure

Phenol red pH indicator is in the medium

Carbohydrate fermentation(glucose,lactose,sucrose)-(triple Sugar Iron Agar(TSI))-Interpretation


Hydrogen sulfide production(triple sugar Iron agar slant)-reaction

na thisulfate--->S reduction enzymes---->H2S

Hydrogen sulfide production(triple sugar Iron agar slant)-procedure

Ferrous sulfate is in the medium

Hydrogen sulfide production(triple sugar Iron agar slant)-interpretation

Black=hydrogen sulfide(+)

starch hydrolysis(starch agar)-reaction


Starch hydrolysis(starch agar)-Procedure

Add gram's iodine to cover surface of plate

Starch hydrolysis(starch agar)-interpretation

(+) clear area in medium around growth, starch hydrolyzed
(-)Dark area around growth, staach not hydrolyzed

Casein hydrolysis(skim agar)-reaction

Casein--->caseinase--->Polypeptides & amino acids

Casein hydrolysis(skim agar)-interpretation

(+)clear area around growth, casein hydrolyzed
(-)no change in medium around growth

Gelatin Hydrolysis(nutrient gelatin deep)-Reaction

Gelatine--->gelatinase---->Polypeptides & amino acids

Gelatin hydrolysis(nutrient gelatin deep)-procedure

Refrigerate or chill before reading

Gelatin hydrolysis(nutrient gelatin deep)-interpretation

Medium is liquid, gelatin was hydrolyzed(+)
Medium remains solid, gelatin was not hydrolyzed(-)

Urea hydrolysis(urea broth)-reaction

Urea + 2h20--->urease--->ammoinia+co2+h20

urea hydrolysis(urea broth)-procedure

Phenol red pH indicator is in the medium

urea Hydrolysis(urea broth)-Interpretation

(+)bright pink, urea hydrolyzed
(-)pale amber color, or no change urea not hydrolyzed

Hydrogen sulfide(H2S) production(Peptone iron agar deep)-reaction

Cysteine---> cysteine sulfurase--->H2S + alanine

Hydrogen sulfide(H2S) production(Peptone iron agar deep)-Procedure

Iron sulfate is in the medium

Hydrogen sulfide(H2S) production(Peptone iron agar deep)-interpretation

(+)Black precipitate, H2S produced
(-)No black precipitate, no H2S produced.

MacConkey Agar

growth=gram negative-red/pink lactose perfementer, colorless=non lactose fermenter
no growth=non gram negative.

Please allow access to your computer’s microphone to use Voice Recording.

Having trouble? Click here for help.

We can’t access your microphone!

Click the icon above to update your browser permissions above and try again


Reload the page to try again!


Press Cmd-0 to reset your zoom

Press Ctrl-0 to reset your zoom

It looks like your browser might be zoomed in or out. Your browser needs to be zoomed to a normal size to record audio.

Please upgrade Flash or install Chrome
to use Voice Recording.

For more help, see our troubleshooting page.

Your microphone is muted

For help fixing this issue, see this FAQ.

NEW! Voice Recording

Click the mic to start.

Create Set