Microbiology lab exam 2 part 2

Why is it important to first determine whether growth occurred in a differential medium such as starch agar, before examining the plate for starch hydrolysis?

Because hydrolysis cannot happen unless growth occurs.

If an organism grows in the OF glucose medium that is exposed to air, is the organism oxidative or fermentative?

Could be either.

Differentiate "fermentation" from "anaerobic respiration":

Fermentation- glucose is oxidized. Anaerobic- inorganic compounds reduce nitrates

Differentiate "aerobic respiration" from "anaerobic respiration":

Aerobic- O2 is final electron receptor. Anaerobic- an inorganic compound is the final electron.

Helicobacter pylori bacteria grow in the human stomach. These bacteria produce a large amount of urease. Of what value is this urease to Helicobacter?

Ammonium ion can neutralize stomach acid.

Which organism(s) gave a positive test for starch hydrolysis?

The organism that gave positive test for starch hydrolysis is the Bacillus subtilis. This is due to its hydrolytic enzyme amylase. This was observed after the addition of iodine. There was an obvious clearing around areas of starch hydrolysis.

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

absence, because there is more energy where oxygen is

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

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

why are fermentation tubes evaluated at 24 and 48 hours

24 for carbohydrate source and 48 for peptone source

If Iodine Were Not Available How Would You Determine If Starch Hydrolysis Had Occurred?

A dye called Phadebas can be used to determine if starch hydrolysis had occurred if iodine were not available.

reduction

A reaction in which a species gains electrons.

what would be found in the clear area that would not be found in the blue area of a starch agar plate after the addition of iodine?

Glucose and amylase.

Is nitrate reduction beneficial or harmful to farmers?

HARMFUL- plants use nitrate as a nutrient. When nitrate is reduced to nitrous oxide or nitrous gas, the soil is depleted of nitrates

Why look for black precipitate (FeS) in the butt instead of on the surface of an H2S test?

Hydrogen sulfide formed @ the surface of the tube can escape as a gas. In the butt, hydrogen sulfide will combine with ferrous sulfide.

If an organism metabolizes glucose aerobically, what result will occur in the fermentation tubes?

Increase acid production, turning it yellow and producing gas in the tubes

In a blue diaper syndrome, a baby's urine turns blue in its diapers following the administration of oral

It is caused by a defect in tryptophan absorption. Bacterial degradation of tryptophan in the intestine leads to excessive indole production and thus to indicanuria which, on oxidation to indigo blue

What would the organism use for energy?

Peptone

When canned foods spoil, what causes the blackening of the cans?

Reduction of sulfur in various compounds forms hydrogen sulfide. The H2S reacts with metal ions (e.g. ferrous ions) to form metal sulfides, which are black.

In the nitrate reduction test, what does the presence of gas indicate?

That nitrogen gas was formed

Aerobic organisms degrade glucose, producing carbon dioxide and water. What acid turns the indicator yellow?

carbonic acid

How can you tell from OF glucose medium whether an organism uses glucose aerobically? ferments glucose? doesn't use glucose?

The organism will produce acid in the open tube only and the indicator will turn yellow in the top of the open tube. If carbohydrate is metabolized in both tubes, fermentation has occurred. These results will have a dark blue color due to ammonia production and the peptone is used instead of carbohydrate.

Why does hydrogen peroxide bubble when it is poured on a skin cut?

There is a catalase enzyme present on our skin and it cause the hydrogen peroxide to seperate.

A person changing a baby's wet diaper smells ammonia. Why?

Urea in the urine is hydrolyzed by bacteria from the baby's feces

Could an organism be a fermenter and also be both MR and V-P negative? Explain...

Yes, some fermenters could produce excess neutral products other than acetone, such as alcohol and lactose acid

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

because amylase leaves the bacteria and spreads out into the agar.

if a bacterium cannot ferment glucose, why not test it's ability to ferment other carbohydrates?

because glucose is a monosaccharide and is already in it's simplest form, other carbohydrates would need to be broken down into monosaccharydes

How could you determine whether a bacterium fermented the following carbohydrates, mannitol,sorbitol,adonitol,or arbinose?

color change and form of gasses The basics is that whenever you want to try to detect a sugar or sugar alcohol fermenter, use a medium with pH indicator since fermenters break down sugar/sugar alcohols to acid. If you use phenol red, fermenters of the sugar alcohol will turn the agar yellow; if you use neutral red, it becomes deep red/pink. Non-fermenters are forced to use peptone instead of the sugar alcohol where the process will liberate ammonia that causes the agar medium to turn alkaline, thus changing the neutral red to lighter pink, somewhat colourless.

Decarboxylation of an amino acid results in the evolution of carbon dioxide. Would a gas trap, such as that used in a fermentation test, be an accurate measure of decarboxylation?

decarboxylation happens when pyruvate is converted to acetyl CoA, which happens in every cell type. So again, you could determine *that* decarboxylation is taking place, but *not* from where.

What would you find in the liquid of hydrolyzed gelatin?

growth of bacteria

what would happen if an organism used up all the carbohydrate in the fermentation tube

it would use acetonin and become basic turning pink

Nutrient gelatin can be incubated at 35°C. What would you have to do to determine hydrolysis after incubation at 35°C.?

sit the tubes in ice for 5 minutes so it can cool to 20°C. If bacteria eat the gelatin it turns to a liquid. If bacteria do not eat gelatin it stays solid. Bacteria who eat gelatin are hydrolysis +.

What is the source of urea in the body?

which ammonia is converted to urea kidneys

Could an organism be both MR and VP positive? Please explain?

yes an organism can be MR & VP positive both. for example staphylococcus.