Microbiology Final Exam

Total magnification =

objective x ocular (10x)

width of pointer at 10x objective

size of object = 25um

width of pointer at 40x objective

size of objects = 6um

width of pointer at 100x objective

size of object = 2.5um

Why do we incubate plates inverted?

To prevent condensation dripping onto the colony, which prevent them from forming colonies

What features can be seen on a wet mount that's not visible on a stained slide?

motility

What features can be seen on both the wet mount and the stained slide? (4)

-size
-shape
-grouping of organisms
-type of organisms

True or False
Microscopes are stored with 40x objective facing down and lenses free of oil.

False, Microscopes should be stored at 4x objective facing down.

True or False
Aseptise technique is important to prevent contamination within your culture and your environment

True

True or False
A plastic capped culture tube is water-tight and can be placed on its side .

False
Often liquid can leak out

True or False
Plastic pipettes are never placed back in its wrapper after use but are immediately discarded into biohazard

True

Why is it necessary to heat fix a bacterial slide specimen before staining?

To prevent bacteria from sliding off the slide

What bacterial structure is Gram stain giving us information about?

Whether there is a thick polypeptidoglycan on the bacteria's cell wall or not

Thick peptidoglycan is a .... cell

Gram positive cell

Thin peptidoglycan is a .... cell

Gram negative
-thin layer can't retain stain, so loses the purple color

What unique structure did we see in Spirillium volutans using methylene blue?

Volutin granules

When doing a streak plate, what must you do with your loop between each set of streaks?

Sterilize the loop with fire to kill off additional bacteria on the loop

Sulfa drugs are structural analogs of which chemical?

PABA

Which step in Gram stain is time sensitive?

decolorization with alcohol 20 - 30 seconds
If too little: both Gram positive and negative will be purple
If too long: both will be pink

what is the purpose of iodine in Gram stain?

To complex crystal violet

For a valid plate count, the number of colonies need to fall within _____

30 - 300 colonies

Which of the following plate would be consider countable?
A. 15
B. 55
C. 124
D. 526
E. 1325

B and C

Agar melts at approximate

100 degrees

At when temperature does agar starts to solidify?

45 degrees

In aerobe/anaerobe experiment, why do we need to keep the melted agar deeps in boiling water for about 10 minutes instead of cooling them directly to 50 degrees?

To boil off the oxygen in the tube so anaerobes can grow

What does it mean for a compound to be bacteriostatic?

The compound does not kill bacteria. However, it inhibits its growth my competing for the binding site

In clinical labs, isolated colonies are often restreak onto another plate. Why?

To get a more pure culture

What feature of Bacillus allows it to survive in temperatures that would kill E Coli?

Bacillus produce endospores that could stand extreme conditions, including heat. E coli does not produce endospore

What does UV light do to the bacteria to kill them upon exposure?

UV light causes neighboring pyrimidines to bind to each other, distorting the shape of DNA which prevents DNA replication

UV light often causes DNA to form....

thymine dimers

Why can't UV light be used to sterilize media under a Petri dish lid?

UV light can't penetrate glass

True or False
Strep. salivarius undergoes a change in genotype when in the presence of sucrose.

False
S. salivarius only undergoes phenotype changes since the genome stays the same, but different genes got turned on

What is the purpose of glucose salt + E coli tube in the sulfa drug experiment? What does the result mean?

-The tube is to ensure E coli will grow (positive control)
-The growth shows that the E coli is functional and should grow in other tubes if sulfa does not inhibit it

To find the original sample of bacteria (formula)

colonies 1/dilution 1/amount plated

What specifically does Agrobacterium do to cause crown gall?

It introduces a Ti plasmid into the host's genome which codes for tumor-like growth in the plant roots

How does Agrobacterium benefit from crown gall?

The plant produce opines, which is a molecule that Agrobacterium can use as fuel and only few bacteria can uses it. This makes Agrobacterium grow without competition

TSY + sucrose is an example of ____ medium

differential
Since the medium grows the bacteria we inoculated and differentiates between two different forms

Strep. salivarius use sucrose to make ____, so the colonies look like gumdrops

capsules

What cellular activities are occurring during the lag phase of bacterial growth?

The cells are producing proteins and are undergoing metabolic activities. The amount of cells stay constant

Generation time calculation

time/generation

What does a positive catalase test looks like?

Bubbles/gas produced

Why do you need to cool gelatin before you can interpret the results?

Gelatin is in liquid form at 37 degrees. So you need to freeze it to determine if gelatin can solidify before concluding the results

If pH indicator were left out of the sugar fermentation media, how would the results be affected?

You wouldn't know if there's any sugar metabolism since there's no color change. However, you can still determine if there's gas production. So, you can't make a definite determination

Why do we use spread plates instead of pour plates for the soil experiment?

Using spread plates avoid heating the agar up to 50 degrees, which can kill some bacteria species in the soil

True or False
No growth in lactose ferments broth indicates that bacterium cannot ferment glucose

false

At what temperature (what does the graph look like) would a bacteria have a shorter generation time?

higher temperature with a graph that slopes up faster than the others

In order to take up naked DNA from the environment, bacteria must be....

competent

In the DNA mediated transformation lab, you inoculated DNA DNase, and Trp- as a control. Why?

To rule out the transfer of DNA isn't because of transduction via a phage

What's is a protoroph?

The wild type, can grow and make all the proteins needed.

Auxotroph

mutant that can't synthesize certain proteins
-need more complex nutrient media to grow

How does laurel lactose sulfate broth selective?

It's a detergent that inhibits growth of Gram positive cocci and rods and Gram negative cocci

How is the laurel lactose sulfate broth differential?

It differentials between lactose fermenters and non lactose fermenters

Why do we test for indicator organisms rather than pathogenic ones?

-Pathogenic ones often exist in low amount and are hard to detect
-We often don't have any health guides to treat pathogenic ones

Why do we expect a higher fraction of streptomycin resistant E coli than in broth not containing an antibiotic?

Antibiotic selects for the antibiotic resistant mutants, while normal broth does not have the selective pressure

True or False
Phage can replicate without a bacterial host.

False
Phage needs a host for replication

In what relative population density do V. fischeri cells produce light?

high density

What causes clear plaques that characterize virulent phages?

Phages are in the lytic cycle and are replicating within the host, lysing the cells when they exit

What causes cloudy plaques that characterize temperate phages?

Some phages are in the lysogenic phase and the DNA are incorporated into the genome. So no lysing of the cell since no viral proteins are produced. However, some are in lytic phase and will lyse the cell

What's the morphology, metabolic capabilities, and identification of the dark colored colony on EMB plate?

Enterobacter
lactose fermenter
Gram negative rods

What are the morphology, metabolic capabilities, and identification of the colonies with green metallic sheen?

E coli
lactose fermenter
Gram negative rods

Narrow spectrum antibiotics

Can kill a a small amount of bacteria

Broad spectrum antibiotics

Can kill wide range of bacteria

What would the Bacillus cells look like after the decolorization step of endospore stain for endospores?

Green

What would the Bacillus cells look like after the decolorization step of endospore stain for vegetative cells?

Clear/colorless

What is the function of autoinducers in bioluminescent bacteria?

To detect the population density and determine if it's big enough to produce light

Over prescribing antibiotics have what effect on bacteria?

Create more antibiotic resistant bacteria since antibiotics select for the resistant mutants

True or False
Urine in the bladder is normally sterile

true

Where do bacteria that cause UTI normally come from?

Patient's own fecal microbiota

A urine sample contains high numbers of many different kinds of bacteria. What does this mean?

The collection method is poor since it's most likely contaminated with skin microbiota

Strep. pyogenes (Group A strep) grow on blood agar will have ____ clearing around colonies, indicating ___ hemolysis

complete, beta

In immunoprecipitation, antigen is ____ until antibodies bind to it, forming ___ protein complex

soluble.... insoluble

Describe one way that antibodies interfere with pathogen's ability to cause disease

Antibodies receptor binds to specific epitome on the pathogen, preventing the pathogen from binding to the host cell to cause infection

A scientist takes the liquid media from the culture of bioluminescent bacteria grow at high density and adds it to cells of the same species growing at low density. The recipient cells, which remain at low density, begin to bioluminesce. Why?

The liquid media contains the high concentration of autoinducers. When transferred to the low density colony, the large amount of autoinducers cause the cells to produce light

Will lambda lysogen be immune to superinfection by bacteriophage (different type of phage)

No, because it's a different type of phage, the bacteria needs to produce a different repressor protein to stop the new phage to produce viral proteins

E coli K12 lambda will produce what kind of clearing when infected the host E Coli k 12?

semi clearing since lambda is a lysogen