Microm 302 Quiz 4

UW

How do you narrow down the identify an unknown bacterium?

Determine its shape and Gram stain reaction

What is the definition of turbid?

Cloudiness due to bacterial presence

Why should you mix a suspension before taking a sample?

Some organisms tend to sink in broth, so it's important to mix it before taking a sample.

What does "streaking" imply?

It implies streaking for isolation

What is the difference between a broth and a solid culture?

A solid culture is typically more concentrated than broth.

How much of a colony should you take when making a smear?

A light touch since you'll use it again to streak

Why would you re-streak an isolated colony?

To ensure you have a pure culture

Why should you save plates from an ongoing experiment?

So you always have a source of the organism being studied until you know an inoculated culture has grown

What is the purpose of a saline suspension?

Ensures a relatively uniform and light inoculum in each biochemical test

What happens if an organism makes enzymes to hydrolyze gelatin?

It will cause the solidifying properties of gelatin to be lost, so the gelatin will liquify as the organism grows

How can you check if an organism is able to break down gelatin?

By putting your sample in a can of cold water. If it is still liquid after 10 mins, this is a positive result.

What is tryptone broth?

It is a broth with high levels of amino acid tryptophan

What can tryptophan be broken down into and by what?

Some bacteria can break down tryptophan to produce indole, a byproduct of tryptophan metabolism

How can indole be detected in a biochemical test?

A colored indicator, Kovac's reagent, can be added and will be red at the top for a positive result, and yellow-brown for a negative result

What is in a sugar fermentation broth and in the tube?

Sugar and a pH indicator are in the broth, and a Durham vial is an inverted tube at the bottom on the tube to trap any gas that is created as a byproduct of the carb fermentation

Is a sugar ferment a good environment for bacteria to grow?

Yes because they are a nutritionally complete media

What will a positive sugar ferment test look like?

The acidic end products of fermentation will lower the pH = pH indicator will turn pink. Gas may also be present trapped under the Durham tube.

What does NG stand for?

No growth

What does NC stand for?

No change

What does A stand for?

Acid

What does AG stand for?

Acid and gas

What are NG, NC, A, AG used to explain?

Sugar ferment results

What does it mean that sulfonamides are selectively toxic?

They are more harmful to bacteria than to humans

How is a sulfonamide selectively toxic?

It interferes with the biochemical folic acid pathway

Why do humans and bacteria need folate?

It forms part of coenzyme F that is needed for certain amino acid and nucleotide synthesis

Do bacteria or humans produce their own folate and how?

Bacteria make their own folate from the precursor PABA. Humans need to get it from their diet

What is the difference between bacteriostatic and bactericidal?

Bacteriostatic agents inhibit bacteria without killing them and bactericidal agnets will kill bacterial cells

Are sulfonamides bacteriostatic or bactericidal?

Bacteriostatic

How do PABA and sulfa work in the folate pathway?

Sulfa will compete for the active site and competitively inhibit PABA. Sulfa and PABA are similar molecules so the enzyme will won't be able to distinguish the two.

What are 2 ways competitive inhibition can be reversed?

by adding excess PABA, which can outcompete sulfa for the active site. Or By non-competitve reversal, where excess end products (amino acids and nucleotides) can be added

What is the folate pathway?

PABA (inhibited by sulfa) -> Folate -> Coenzyme F -> amino acid/nucleotide synthesis

Obligate aerobes

Need oxygen and produce catalase (Micrococcus luteus)

Obligate anaerobes

Killed by oxygen, don't produce catalase (clostridium sporogenes)

Facultative anaerobes

can use oxygen but don't need it since they can ferment and produce catalase. (E coli)

Why do we boil a sample for 10 mins?

To get rid of any oxygen in the sample

How can you evenly distribute micoorganims in a tube?

Roll it between your hands

How can vegetative cells be killed?

By boiling, but not all can be killed

What are endospores?

They are resistant cell forms that can withstand starvation, desiccation, extreme temp and pH, irradiation

What causes botulism?

Clostridium botulinum

What does equilibrated mean?

to be in equilibrium

Why do we have controls in experiments?

To compare results of an experiment

Why are samples incubated?

To determine is there are any viable cells in a sample remaining

At what temp is e coli killed

70C

At what temp is bacillus endospores killed?

Above 100C

What is UV light used for and when/not?

To disinfect by destroying airborne organisms. It is not used for things glass/plastic since it penetrate it.

How does UV light affect organisms?

Causes mutations by causing thymine dimers to form to the point where the repair system is overwhelmed

What should you do when operating UV light?

wear safety goggles or place hands under the light

What is the name of the normal microbiota in the mouth and where?

Streptococcus salivarius on the tongue

How does S. salivarius grow into a gumdrop?

It can use sucrose to produce a polysaccharide capsule. otherwise they grow small and white

What is phenotype?

Observable characteristic

Genotype

Total genetic information

How is dental plaque made?

Streptococcus mutans makes a capsule and sticks to the tooth and lets other bacteria stick

How are cavities made?

The bacteria on the plaque can produce acid which eats away at the tooth enamel

What is a differential medium?

Allows the growth of a variety of organisms, but makes one type or group distinctive in apperance.

What is the lag phase?

Cell number is constant although metabolism is happening

What is the exponential/log phase?

When cells multiply rapidly

What is the stationary phase?

When nutrients are depleted and toxic metabolic activity is for maintenance function (not growth). No net cell increase (death = growth)

What is the death phase?

Rate of cell death increases

What is the definition of generation time?

Amount of time it takes cells to double in number

What is Nitrogen fixation?

Organisms convert N2 into ammonia which then go into organic compounds. Earth would run out of organic N without it

Who does N fixation?

Prokaryotes including many soil bacteria (azotobacter, clostridium, klebsiella)

What micoorganisms can make antibiotics?

Soil ones. Penicillin from fungus Penicillium, streptomyces, bacitracin from bacillius

What are geosmins

chemicals that give soil characteristic earthy odor

How long ca endospores stay viable?

50 to thousands of years

What can soil microbes cause?

Tetanus from clostridium tetani/botulinum endospores inoculate into tissue and germinate. and botulism

What are spread plates?

Add dilute sample spread over agar surface.

How are streptomyces colonies and bacillus endospores differentiated in a test?

Heat kills the vegetative cell not the endospores.

What is different about staining spores?

They are stain resistant so gram stain doesn't work well. They appear as colorless body

How do you stain endospores?

1. cover smear ONLY with piece of paper towel

2. saturate with malachite green

3. heat slide over boiling water for 10 mins and keep paper towel saturated

4. rinse with water and flood with water to decolor

5. counterstain with safranin for 1 min

Vegetative cells will safranin (pink) stain but endospores won't and will be green.