lab questions
which of the following could be considered virulence factors for Staphylococcus aureus? -mannitol fermentation -DNase -coagulase -growth in high salt environments
-DNase -coagulase
match the following bacteria with their color after gram staining (pink or purple) -E. coli -Staphylococcus aureus -Neissera gonorrhoeae -Salmonella typhi
-E. coli --> pink -Staphylococcus aureus --> purple -Neissera gonorrhoeae --> pink -Salmonella typhi --> pink
What do each of the three control quadrants tell you about your material and methods? Some might give you multiple pieces of information. (Consider the list above.)
-StrS sector: growth in this sector could indicate your strains are not what you think they are or your agar plate does not have the correct amount of streptomycin (too much or too little) -StrR sector: lack of growth in this sector could indicate your strains are not what you think they are or your agar plate does not have the correct amount of streptomycin (too much) -StrS cells + DNase + DNA: growth in this sector could indicate your DNA is contaminated by the original resistant strain, something besides transformation is occuring
which of the following reagents would you need to perform a direct ELISA? -an antibody against the protein you are testing for -an anti-antibody -a chromogenic substrate for the enzyme linked to an antibody -a labeled competitive protein
-an antibody against the protein you are testing for -a chromogenic substrate for the enzyme linked to an antibody
capsule staining is different from other classic microbiology staining protocols because : (select all that apply) -capsule staining only uses one dye as compared to all staining protocols where two or more dyes are used -capsule staining does not use heat fixation, as other staining protocols do, to preserve capsule structure -capsule staining is a negative staining protocol, compared to many other staining protocols that are positive staining -capsules are specialized microorganism structures and require different techniques to visualize
-capsule staining does not use heat fixation, as other staining protocols do, to preserve capsule structure -capsule staining is a negative staining protocol, compared to many other staining protocols that are positive staining -capsules are specialized microorganism structures and require different techniques to visualize
capsule staining is different from other classic microbiology staining protocols because: select all that apply -capsule staining only uses one dye as compared to all staining protocols where two or more dyes are used -capsule staining does not use heat fixation, as other staining protocols do, to preserve capsule structure -capsule staining is a negative staining protocol, compared to many other staining protocols that are positive staining -capsules are specialized microorganism structures and require different techniques to visualize
-capsule staining does not use heat fixation, as other staining protocols do, to preserve capsule structure -capsule staining is a negative staining protocol, compared to many other staining protocols that are positive staining -capsules are specialized microorganism structures and require different techniques to visualize
negative staining
-cell is clear/colorless -background is stained dark/black -india ink -nigrosin
positive staining
-cell is colored by dye -background is not stained -methylene blue -crystal violet
please match the following chemicals with their function -crystal violet -safranin -ethanol -iodine -counterstain -decolorizer -primary stain -mordant
-crystal violet --> primary stain -safranin --> counterstain -ethanol --> decolorizer -iodine --> mordant
as you create your smear from a sample on solid media, it is important to use an appropriate amount of material and evenly disperse the organism onto the surface of the slide. which of the following can occur due to using excessive material as you create a smear preparation? select all that apply -it will be difficult to apply stain correctly to the slide for visualization -it will be difficult to distinguish bacterial cell morphology and arrangements of cells on the smear sample -it will be difficult to remove excess dye stain in later steps of the smear procedure -it will be difficult to sterilize the slide after the procedure is complete
-it will be difficult to apply stain correctly to the slide for visualization -it will be difficult to distinguish bacterial cell morphology and arrangements of cells on the smear sample -it will be difficult to remove excess dye stain in later steps of the smear procedure
what are two purposes of heat fixing?
-making the bacteria adhere to the slide -making the bacteria permeable to the dye
why is aseptic technique important during laboratory activities like smear preparation? select all that apply -proper aseptic technique aids in keeping microbes from spreading to other surfaces, where they might be contacted by others in the lab -proper aseptic technique helps prevent contamination from being introduced into your sample during preparation -aseptic technique aids in selecting a treatment, because we can observe what methods kill the infectious agent -aseptic technique helps prevent accidental infection of the handler
-proper aseptic technique aids in keeping microbes from spreading to other surfaces, where they might be contacted by others in the lab -proper aseptic technique helps prevent contamination from being introduced into your sample during preparation -aseptic technique helps prevent accidental infection of the handler
Escherichia coli
-shape: bacilli -arrangement: none -gram character & color after staining: negative / pink
Salmonella typhi
-shape: bacilli -arrangement: none -gram character & color after staining: negative / pink
Neisseria gonorrhoeae
-shape: cocci -arrangement: diplo -gram character & color after staining: negative / pink -expresses alternate forms of pilin to prevent detection by the host
Staphylococcus aureus
-shape: cocci -arrangement: staphylo -gram character & color after staining: positive / pink -blocks the binding of phagocytes to opsonized bacteria
now that you have seen the difference in the smear preparation afters simple methylene blue staining, which of the following is correct regarding your smear now? select all that apply -the addition of methylene blue helps show the intact appearance and localization of the cells, compared with no staining -the addition of methylene blue makes visualizing some bacterial cell characteristics more apparent, compared to no staining -addition of methylene blue highlights the bacterial cell nucleus and organelles that were difficult to discern without stain -the addition of methylene blue helps visualize the shape and arrangements of bacterial cells that were difficult to discern without stain
-the addition of methylene blue helps show the intact appearance and localization of the cells, compared with no staining -the addition of methylene blue makes visualizing some bacterial cell characteristics more apparent, compared to no staining -the addition of methylene blue helps visualize the shape and arrangements of bacterial cells that were difficult to discern without stain
now that you have seen the difference in the smear preparation after simple methylene blue staining, which of the following is correct regarding your smear now? select all that apply -the addition of methylene blue helps visualize the shape and arrangements of bacterial cells that were difficult to discern without stain -addition of methylene blue highlights the bacterial cell nucleus and organelles that were difficult to discern without stain -the addition of methylene blue helps show the intact appearance and localization of the cells, compared with no staining -the addition of methylene blue makes visualizing some bacterial cell characteristics more apparent, compared to no staining
-the addition of methylene blue helps visualize the shape and arrangements of bacterial cells that were difficult to discern without stain -the addition of methylene blue helps show the intact appearance and localization of the cells, compared with no staining -the addition of methylene blue makes visualizing some bacterial cell characteristics more apparent, compared to no staining
what is the purpose of adding a strip of paper to the spore stain procedure? choose all that apply -the paper is protective to the scientist doing the stain -the paper is sticky and removes live bacteria from the smear -the paper helps hold stain away from the sample -the paper keeps the dye from evaporating too quickly during the heating step -the paper allows for more contact time between the dye and spores
-the paper keeps the dye from evaporating too quickly during the heating step -the paper allows for more contact time between the dye and spores
what are the advantages to using a met mound slide preparation? -wet mount slide preparation is a long and difficult process -the specimen behavior can be viewed -the specimen may be alive -the specimen could be viewed moving
-the specimen behavior can be viewed -the specimen may be alive -the specimen could be viewed moving
what are advantages to using a wet mount slide preparation?
-the specimen could be viewed moving -the specimen behavior can be viewed -the specimen may be alive
what is the purpose of heat fixing?
-to kill the cells and make them stick to the slide -denatures enzymes that could break down the cell
streak plate isolation can be used for many reasons. select all situations where someone might apply this technique -when studying an overgrowth of microbes in lake erie -when cloning genes in the lab -when testing the ingredients of a salad bar to find the cause of a food borne illness -when determining the cause of a throat infection
-when studying an overgrowth of microbes in lake erie -when cloning genes in the lab -when testing the ingredients of a salad bar to find the cause of a food borne illness -when determining the cause of a throat infection
if your completed quadrant streak plate showed two different and distinct colony appearances, what could you conclude? select all that apply -your technique was poor, as correct quadrant streak plate protocol would have eliminated all but one species in the sample -your initial bacterial culture inoculum contained two unique bacteria species -your plate was incoulated with a single species, but break in aseptic technique could have allowed contaminant bacteria to also grow -your bunsen burner flame was too hot and caused growth of bacteria too early during the streaking
-your initial bacterial culture inoculum contained two unique bacteria species -your plate was incoulated with a single species, but break in aseptic technique could have allowed contaminant bacteria to also grow
capsule staining procedure
1.) apply primary stain (india ink or nigrosin) to a clean slide 2.) use inoculating loop to aseptically mix bacterial sample with primary stain 3.) create a thin smear by dragging a clean slide through the sample 4.) allow sample to thoroughly air dry 5.) apply secondary stain (crystal violet) to smear 6.) rinse with water and prepare for microscopy
put the following endospore stain steps in the proper order -make a slide smear of B. megaterium -steam the bacteria with malachite green for 5 minutes -gently rinse the slide for 30 seconds -counterstain with safranin for 1 minute -heat fix the slide -rinse the slide for a couple of seconds
1.) make a slide smear of B. megaterium 2.) heat fix the slide 3.) steam the bacteria with malachite green for 5 minutes 4.) gently rinse the slide for 30 seconds 5.) counterstain with safranin for 1 minute 6.) rinse the slide for a couple of seconds
put the following endospore stain steps in the proper order -rinse the slide for a couple of seconds -counterstain with safranin for 1 minute -make a slide smear of B. megaterium -gently rinse the slide for 30 seconds -heat fix the slide -steam the bacteria with malachite green for 5 minutes
1.) make a slide smear of B. megaterium 2.) steam the bacteria with malachite green for 5 minutes 3.) gently rinse the slide for 30 seconds 4.) counterstain with safranin for 1 minute 5.) heat fix the slide 6.) rinse the slide for a couple seconds
when using the plasmid mini prep kit described in the YouTube video, scientist typically start with _____ ml of an overnight culture of bacteria and end with ____ microliters of DNA
1.5 ; 50
to make the 500 ml of TAE buffer for gel electrophoresis, a graduate student needs to mix water and 5X TAE buffer. how much of each does she need?
100 ml 5X TAE buffer and 400 ml water
when using the oil immersion lens on our microscopes, the total magnification of the image would be _____ X
1000X
if the window on a P20 micropipette displays the numbers "1 5 5" from top to bottom, what volume will be measured?
15.5 microliters
a mutation in which of the following would make a bacterium resistant to streptomycin? -mecA -23S rRNA -16S rRNA -transpeptidase
16S rRNA
you have a DNA prep that is 250 micrograms/ml and you would like to load 500 nanograms on a gel. how many microliters should you load?
2 microliters
what is the total magnification of a specimen using the 40X objective?
400X
to create 50 ml of media containing 50 mg/ml kanamycin, how many microliters the 50 mg/ml kanamycin stock do you add to the nutrient broth?
50 microliters
if you wished to make your own hand sanitizer, what concentration of isopropyl alcohol would be the best at killing microbes? -less than 60% -60-70% -90% -100%
60-70%
How would the procedure for making a smear prep differ when you use a culture of bacteria on a plate instead of in a liquid broth?
A small amount of water should be mixed with the bacteria on the slide if the culture is from a plate in order to diliute it
Consider the mechanism of actions for the antibiotics that were effective against all the bacteria. Why do you think these antibiotics seem to be immune to the structure of the cell envelope?
Amoxacillin has an additional amino group that allows it to pass through cell membranes more easily. Ciprofoxacin is a small molecule that is able to pass through the cell membrane more easily
Name two genera of bacteria that are able to form endospores
Bacillus and Clostridium
Why is it important that the TSI test poured as a slant? How might it affect your results if it were poured straight up instead?
By pouring the agar at an angle, it provides a larger surface for oxygen exchange. This allows the bacteria near the top of the tube to use the peptone for energy in aerobic cell respiration. If the tube were not poured with a slant, then there would be very little oxygen in the upper part of the tube and we would not be able to get a two-toned result.
Suggest a reason why some antibiotics were given different diameters for zones of inhibition to determine sensitivity.
Certain zones of inhibition were determined to correlate to in vivo treatments.
Two of the identification tests used for Staphylococci are also virulence factors and benefit a pathogen such as S. aureus to grow in certain environmental conditions or avoid the immune system. Which of the tests are for virulence factors and what benefit does each provide the bacteria when causing disase?
Coagulase: S. aureus produces this enzyme which results in the clumping of proteins in plasma and can use this mechanism to surround itself with a protective layer of protein in order to evade the host phagocytes DNase: allows S. aureus degrade the mesh of extracellular DNA so it can escape neutrophil traps
Did all the antibiotics work equally well on the gram negative strains? Explain.
Differences between Gram Negative: Pseudomonas aeruginosa was more resistant to everything except ciprofloxacin. This is likely due to the fact that in addition to the outer membrane which protects its cell wall-synthesizing enzymes, it also has an efflux pump that pumps out a variety of antibiotics before they can kill
Why might the results of this test not perfectly reflect what works best to treat infections in humans?
Different antibiotics are absorbed at different rates in humans. We may not be able to reach a high enough concentration to kill some bacteria. Some antibiotics may not be stable in stomach acid or the intestines and may need to be injected. Additionally, some antibiotics can only be administered as an intravenous drip. This changes the viability of treatment.
Which additional tests could you do to confirm the presence of a coliform?
Durham Fermentation tube and endospore staining (this would show the bacterial shape as well)
from all your data, what can you conclude about the optimal temperature for E. coli?
E. coli grows faster at 37C than 30C. this is supported by the fact that the slope of the lines in graph 1 and 2 are steeper at 37C than at 30C. in addition, the generation time for the bacteria at 30C is longer than at 37C, indicating it takes longer for E. coli to double at 30C than at 37C
Although most E. coli cells were killed rapidly by UV light, some seemed to survive even after 16 minutes of treatment. How can you explain that?
E. coli likely acquired mutations that hyperactivated its repair systems.
Bacillus megaterium is able to induce endospore formation, yet both cultures of Bacillus megaterium are not equally resistant to UV light. What does that tell you about endospore formation and UV light?
Endospores are typically produced due stress. The bacteria will die in minutes due to UV light so the new B. megaterium are unable to produce endospores before they are killed by the UV light. The old B. megaterium culture already contains endospores before UV treatment so they are better equipped to survive.
Which of the above organisms are coliforms?
Escherichia coli and Citrobacter freundii
What is the MIC of an antibiotic? In a Kirby-Bauer assay, where would you find it? For treatment of an infection in humans, is it better to have an antibiotic with a higher or lower MIC? Why?
It is the minimum concentration required to inhibit growth of bacteria. You want a lower MIC because while the antibiotic may not act on eukaryotic cells, high concentrations can cause liver damage due to having to process large quantities of the antibiotic.
why is the gram stain called a differential stain?
It uses two or more stains and results in the bacteria turning different colors based on their cell wall characteristics.
an undergraduate working in a molecular biology lab loaded 3 samples on an agarose gel: a DNA ladder, uncut plasmid DNA and the same plasmid cut with an enzyme that only cuts in one place. he loaded the DNA ladder in lane 1 but was distracted when loading the other two samples and does not know which is which. the stained gel is shown below. https://learn-us-east-1-prod-fleet02-xythos.content.blackboardcdn.com/5c1270dbb5a74/17168560?X-Blackboard-Expiration=1636059600000&X-Blackboard-Signature=4c6NdNZhhmYFFISL1pSuaB%2FwIzeWxmU%2F8DPEAF59CBw%3D&X-Blackboard-Client-Id=100342&response-cache-control=private%2C%20max-age%3D21600&response-content-disposition=inline%3B%20filename%2A%3DUTF-8%27%27cut%2520and%2520uncut%2520plasmid%2520DNA.jpg&response-content-type=image%2Fjpeg&X-Amz-Algorithm=AWS4-HMAC-SHA256&X-Amz-Date=20211104T150000Z&X-Amz-SignedHeaders=host&X-Amz-Expires=21600&X-Amz-Credential=AKIAZH6WM4PL5SJBSTP6%2F20211104%2Fus-east-1%2Fs3%2Faws4_request&X-Amz-Signature=dfdb7f6eae8eae334968512b1c6983df99a9ab8ea20e11472d151f336ea8beba please explain to the student which lane has the cut and uncut plasmid DNA and how you know that
Lane 2 has the cut DNA and land 3 has the uncut DNA. When you cut a circular plasmid with an enzyme that cuts once, then you should see a single band and that is what is seen in Lane 2. When you run uncut plasmid DNA, you will have mix of supercoiled DNA (which runs faster than linear DNA), nicked DNA and multimers. In lane 3 we see multiple bands and one of them runs faster than the linear cut DNA in lane 2. This is consistent with uncut DNA.
Why was malachite green used to stain the endospore rather than a stain such as crystal violet?
Malachite green doesn't bind well to cell structures so it rinses easily with water
Does the picking of apparently isolated colonies always give pure cultures? Explain.
No it does not. It is possible that two cells are so close to one another that when they replicate to form colonies the piles of cells are merged and our eyes would not be able to detect this. The only way to be sure that you have a culture that was truly pure (made from a single cell) is to pick that colony and restreak it. If you then pick a single from this second streak plate, you are more likely to have a pure culture. Scientists will often repeat the process a third time to ensure purity.
Could any of these organisms on the plates be the potentially lethal food pathogen Listeria? How do you know?
No, Listeria is a gram positive food pathogen so it will not grow on the MacConkey agar because of the crystal violet and bile salts in the media. Hektoen Enteric Agar plates also contain biles salts and therefore select for gram negative bacteria.
Did any of the food products potentially have Salmonella? How do you know?
No, there were no black precipitates formed on the Hektoen Enteric Agar in any of the samples. A black precipitate would indicate the potential presence of Salmonella because this bacteria can reduce sulfate.
Did the same antibiotic work the best on all strains? If not, which worked best on the gram positive strain?
No, they had different efficacies Worked Better against Gram Positive: Penicillin, Erythromycin
Can you determine with certainty that any of the bacteria from the food are coliforms? Why or why not?
No, we cannot say that the colonies are coliforms. From the plates, we are not able to tell if they produce gas during fermentation of lactose, if they are bacilli, or if they form endospores.
what is an advantage of using OD measurements over calculating the cfu/ml?
OD measurements give you an immediate answer that doesn't require overnight growth and is less subject to human error
On the figure below, make a prediction as to which quadrants you expect to see growth
On the plate with NO streptomycin, there should be growth in all sectors except the DNA. If the DNA sector grows, then there are two possibilities for what has happened - either your crude DNA extract was contaminated at some point, or more likely, you did not break open all your bacteria in the extraction procedure and some survived.
what is an advantage of using an SPC over OD measurements?
SPC gives you actual number of cells whereas OD only gives you a relative number
Which of the above organisms are exclusively gastrointestinal pathogens and are not typically members of the human gut flora?
Salmonella typhimurium and Shigella
How would using an acidic or negatively charged stain change the appearance of your image under the microscope?
The cell surface will repel the stain so the background will be stained but the cells will not
What factors about the bacterium or the environment will increase the chances of a successful transformation?
The efficiency of transformation is dependent on having competent cells. Competency is induced by a stressful environment which includes cells dying, the presence of UV light, and lack of food. The factors that induce competency varies amongst bacterial strains and species.
Draw and label the structure of a gram (-) and gram (+) bacterium. Add the transpeptidase enzyme to both figures. Using these figures, explain why some antibiotics are more effective against gram (+) bacteria than gram (-) bacteria
The outer membrane does not allow large or polar molecules to pass through. This can protect the peptidoglycan layer from exposure to beta-lactam antibiotics such as penicillin. Antibiotics like ampicillin and amoxicillin are semi-synthetic antibiotics and have side chains added to the molecule allowing them to pass through the outer membrane. The transpeptidase will be located at the cell wall.
After overnight incubation, observe the turbidity in the tubes and answer the following questions: How do your growth results compare to the parental Staphylococcus strain that has not been exposed to streptomycin?
The parental strain was only able to grow in the absence of added streptomycin. The other isolates were all able to grow in some level of added streptomcyin indicating that they had mutated to be resistant to the antibiotic.
Are the colonies in the area of high streptomycin an induced or natural mutation?
These colonies are an example of natural spontaneous mutation because no physical or chemical treatment affected the DNA of the organism.
When you practiced the transfer of bacteria to a fresh tube of broth using your best aseptic technique, what would have been the purpose of including the following control? Transferring a loop of sterile broth to another tube of broth
This can control for both our transfer technique and whether the broth was sterile in the first place. If we see growth in the inoculated tube after overnight incubation, this could suggest that either our technique was not good and we contaminated our tube or that the broth wasn't sterile at the start. Either way, this should call in to suspect the tubes we inoculated with bacteria. The growth we see might not be due to the bacteria we planned to add, but instead comes from another source.
After overnight incubation, observe the turbidity in the tubes and answer the following questions: What is the significance of this experiment to human activities and the treatment of infectious disease?
This experiment shows how quickly bacteria can develop mutations to become antibiotic-resistant and stresses the importance of proper prescription use, limiting the use of antibiotics in food, and the maintenance of good hygiene. There are last resort antibiotics that can be used but they have a number of side effects.
How exactly does UV light kill microorganisms?
UV light causes pyrimidine dimers (such as thymine dimers) in DNA which causes the DNA to bend. The dimer prevents DNA polymerase from continuing replication.
Controls are set up to help you prove the conclusions you make from an experiment. In this experiment, what is is it we are hoping we can conclude?
What we are hoping to conclude is that the StrS cells took up DNA and were transformed to become StrR. The controls help us prove this by showing: · StrS cells are actually sensitive · There is enough streptomycin in the plate to kill non-resistant cells · There isn't too much streptomycin so that it kills resistant cells · The rate of spontaneous mutation by strep sensitive cells to resistant forms · The appearance of streptomycin resistance in our transformation sector is a DNA dependent event
Should we consider these non-coliform counts in determining whether a food is safe to ingest? What species could these be and are they dangerous?
Yes! Enteric pathogens like Salmonella and Shigella are not coliforms but cause GI infections in humans. Shigella and Salmonella do not ferment lactose to produce acid and gas.
Do the results of all the different media agree? Explain.
Yes, for example sulfate reduction was seen for organism one on the HE plate and lactose fermentation was seen for organisms 4 on the EMB plate, HE plate, and TSI tube.
Do you see a gradient of growth to match the streptomycin concentration gradient?
Yes, more growth on the side with no streptomycin and less growth on the side with a high concentration of streptomycin. This is because resistant bacteria may be able to survive in the high concentrations of streptomycin but the streptomycin sensitive bacteria cannot.
Do any of the foods potentially contain coliforms? Which ones and how do you know?
Yes, the 52 colonies appeared red on MacConkey agar meaning that the bacteria fermented lactose and it's gram negative. These results are confirmed by the yellow color on the Hekton Enteric agar further indicating that sugar fermentation created an acid.
Based on what you know about each of the three cultures, do the results makes sense? Please explain.
Yes, the old B. megaterium will have started to produced endospores which will make them much more diffcult to kill under the UV light because it created endospores due to nutrient depletion.The new B. megaterium will show decreased growth under lengthened exposure to UV light because they will not be able to preserve their DNA in endospores. E. coli is microbe typically found in the gut and not exposed to much UV light therefore it would not be expected to have a high tolerance to UV light. B. megaterium is a soil microbe that would have some exposure to UV light so it would need more defenses.
based on what you learned in this simulation, for which of the following samples would you skip the heat fixation step? -a sample of pond water, looking for living bacterial activity such as observing for mobility -a sample of patient sputum that you want to stain with heated carbol fuchsin dye, looking for tuberculosis -a sample of patient blood that you want to stain, looking for bacterial infection
a sample of pond water, looking for living bacterial activity such as observing for mobility
cells can become resistant to beta-lactam antibiotics by which of the following mechanisms? -conjugation -transformation -spontaneous mutation -all of the abvoe
all of the above
the evolution of influenza virus that causes relatively mild and limited disease epidemics is referred to as:
antigenic drift
why is it important to determine the generation time of the bacteria from data measured during the exponential phase?
because during this phase the cells are growing at their fastest rate
the organism that causes Strep throat will display _____ hemolysis on a ______ plate and be bacitracin ________. another name for this organism is group ____ Strep. this is to differentiate it from group ____ Strep which appears as ______ hemolytic on a blood agar plate but causes severe infections in newborns
beta ; blood ; sensitive ; A ; B ; beta
Mycobacterium tuberculosis
blocks phagosome-lysosome fusion
both the gram staining and endospore staining procedures are considered differential staining techniques. explain why
both techniques use two or more dyes, which turns the bacteria different colors depending on their unique characteristics
what is the purpose of skipping the heat fixation step in the capsule stain procedure? -capsules are fragile and can be destroyed with heating -heat fixation is unnecessary in capsule staining because the organisms are harmless -capsules are converted to slime layers if heated -heat fixation is unnecessary because organisms with capsules naturally adhere to the slide -capsules will appear too dark if heated
capsules are fragile and can be destroyed with heating
what is the purpose of skipping the heat fixation step in the capsule stain procedure? -heat fixation is unnecessary in capsule staining because the organisms are harmless -heat fixation is unnecessary because organisms with capsules naturally adhere to the slide -capsules are converted to slime layers if heated -capsules are fragile and can be destroyed with heating -capsules will appear too dark if heated
capsules are fragile and can be destroyed with heating
the best test to differentiate Streptococci from Staphylcocci would be the ________ test
catalase
the bubbling above occurred when hydrogen peroxide was dropped on the plate of bacteria. the enzyme _____ causes this bubbling when it converts hydrogen peroxide into water and _____
catalase ; oxygen
What was the position of the endospore on our B. megaterium?
central
which type of ELISA will allow you to quantitate a protein by testing its ability to displace the binding of a labeled protein of the same type?
competitive
you isolated 50 microliters of plasmid DNA using a mini prep kit. the spectrophotometry readings for this DNA are: -260 nm = 0.220 -280 nm = 0.089 what is the concentration of your DNA prep? is this DNA pure?
concentration = 11 micrograms/ml purity = 2.47, NOT pure
of the following methods for genetic transfer, which is the only one that requires direct cell-cell contact? -transformation -conjugation -transduction
conjugation
which of the three factors affecting image quality is altered by the light source? -contrast -magnification -resolution
contrast
which of the three factors affecting image quality is altered by the light source? -contrast -resolution -magnification
contrast
after performing the schaeffer fulton stain, the _____ appeared green and the ____ cells looked pink
endospore ; vegetative
after performing the schaeffer fulton stain, the _____ appeared green and the______ cells looked pink
endospores ; bacterial
Trypanosoma brrucei
gene conversion
please explain why gram negative bacteria tend to be more resistant to beta-lactam antibiotics than gram positive bacteria
gram negative bacteria have an outer membrane that prevents the antibiotics from accessing transpeptidase. gram positive bacteria have no outer membrane so there is nothing that prevents antibiotics from binding to and inhibiting their cell wall enzymes
what should the results in the graph relating OD to cfu/ml look like?
graph should be a straight line because there is a direct relationship between the number of cells and the turbidity of the culture. since temperature has no effect on this relationship, the lines for the 2 cultures should be on top of one another.
please explain how the improper use of antibiotics has contributed to the rise in antibiotic resistant bacteria
if someone with a bacterial infection, they are infected with a population of bacterial with a range of antibiotic resistance. when they begin taking an antibiotic only the least resistant bacteria die off. it takes longer to kill the more resistant bacteria in the population. if then, the person stops taking their antibiotic prematurely, they leave behind the most resistant bacteria which are able to grow, potentially making the person sick again. this time, they have many more resistant bacteria in the population and it is likely they won't be able to use the same antibiotic. they have selected for resistant bacteria like we did when we plated on the gradient plate
why is it important to push the plunger to the first stop when drawing up liquid?
if you go to the second stop, you will measure too much liquid
what is important to remember when using oil immersion? -immersion oil can only be used with the 100X objective, and without it, the image is blurry -immersion oil increases the magnification of the 100X objective lens -immersion oil helps with resolution with all objective lenses
immersion oil can only be used with teh 100X objective, and without it, the image is blurry
what is important to remember when using oil immersion? -immersion oil can only be used with the 100X objective, and without it, the image is blurry -immersion oil helps with resolution with all objective lenses -immersion oil increases the magnification of the 100X objective lens
immersion oil can only be used with the 100X objective, and without it, the image is blurry
if an MR test for a bacterium turns red, what assumption can you make about that bacterium? -it would turn a lactose durham tube yellow -it would turn a glucose durham tube yellow -both A and B -you cant make any assumptions about the durham tube
it would turn a glucose durham tube yellow
for the hand washing experiment, the plates were incubated in a 37 degree celcius incubator. why do you think this temperature was chosen?
left at room temperature so that growth of the microbes from the fomites are in their normal temperature environment
DNA is _______ charged and runs towards the ______ pole during electrophoresis
negative ; positive
when a mother is Rh _____ and a father is Rh _____, hemolytic disease of the newborn is a complication that can arise during their ______ pregnancy. this will happen if the first baby was Rh ______ and the second baby is Rh ______. this is because Ig___ antibodies can cross the placenta and attack the baby's blood
negative ; postive ; second ; positive ; G
due to the time restriction of 90 minutes, we did not see a full growth curve of E coli. looking at your graph, which phase(s) of growth do you see for the two cultures?
only log phase
which of the following patterns is used to streak an agar slant? -pass the loop across the surface of the slant -pass the loop across the surface of the slant and push the loop completely to the bottom of the tube -pass the loop across the surface of the slant and cut several lines into the agar making a grid pattern
pass the loop across the surface of the slant
a family member is afraid they were exposed to the virus a few days ago and would like to be tested for SARS-CoV-2. please explain to them which type of test they should get and why. give a brief explanation of the test so that a non biologist can understand how it works
since the family member has only recently been exposed to the virus, it is unlikely they would have begun to make antibodies yet. therefore testing for antibodies using the quick lateral flow antibody test would not be useful and would likely give a false positive. a better test for this person would be the test for the virus itself using the RT-PCR test. the test takes your saliva or mucus and tests for the virus there. a sample is taken from the patient, any virus in it is broken, open to release its genetic material and then that genetic material is amplified by enzymes. if the virus is there, the lab tech will be able to detect the DNA once it is amplified. if there is no virus, then nothing gets amplified and the test is negative
a student with a boil on their arm went to student health where the pus was swabbed. this cotton swab was then sent to a lab to identify the cause of the infection. what would be the first two things that would need to be done to identify this microbe?
streak for singles to isolate pure cultures of whatever is growing and gram staining
explain how hand sanitizer works to kill bacteria
the alcohol in hand sanitizer denatures and unfolds proteins, along with killing any bacteria that has a membrane
both the gram staining and endospore staining procedures are considered differential staining techniques, why?
the both use more than two dyes and the cells will look different depending on their structures
after gentle lysis, a culture of bacteria is spun in a microcentrifuge and separated into a pellet and supernatant. which of the following is true about thee two fractions?
the chromosomal DNA is in the pellet and the plasmids are found in the supernatant
what is the advantage of starting with the 4X objective before moving to the 10X and then the 40X objective?
the field of view is larger, and it is easier to focus
what is the advantage of starting with the 4x objective before moving to the 10x and then the 40x objective? -the field of view is larger, and it is easier to focus -the field of view is easier to focus -the field of view is larger
the field of view is larger, and it is easier to focus
how do the coarse and fine focus knobs work on a brightfield microscope? -the focus knobs move the eyepieces farther apart or closer together -the focus knobs move the stage toward and away from you as you are looking at the microscope -the focus knobs move the stage up and down
the focus knobs move the stage up and down
how do the coarse and fine focus knobs work on a brightfield microscope? -the focus knobs move the stage towards and away from you as you are looking at the microscope -the focus knobs move the eyepieces farther apart or closer together -the focus knobs move the stage up and down
the focus knobs move the stage up and down
in the conjugation experiment in the virtual lab, both the antibiotic resistant P. aeruginosa and the antibiotic sensitive Acinetobacter were plated separately on plates with and without antibiotics. what was the purpose of all four of these plates?
the goal is to show that both strains are able to grow in the lab (on the plate without antibiotics) and to verify their antibiotic resistance or sensitivity (on the plate with antibiotics)
when viewing a live, unstained prep of cells, how should the iris diaphragm be adjusted and why?
the iris diaphragm should be closed to increase contrast on the slide. with an increased contrast, you will be able to see everything very clearly, even the smallest microbes
if we had included an old culture of e.coli in our UV experiment, do you expect it would have been as resistant to UV light as the old culture of b. megaterium? please explain
the reason b. megaterium became resistant to UV when it aged is that it was able to form endospores which are UV resistant. e.coli is not able to make endospores so stress (like aging) would not make them UV resistant
why should the fine focus knob typically be used with the 10X and 40X objective lenses?
the slide should be close to in focus after focusing at the 4X objective. focusing the coarse focus knob would result in too large a change in focus
why should the fine focus knob typically be used with the 10x and 40x objective lenses? -the slide should be close to in focus after focusing at the 4x objective. focusing with the coarse focus knob would result in too large a change in focus -focusing using the coarse adjustment knob with the 10x or 40x objective may crack the stage -the coarse focus knob is nonfunctional with the 10x and 40x objective lenses
the slide should be close to in focus after focusing at the 4x objective. focusing with the coarse focus knob would result in too large a change in focus
you are observing Streptococcus pneumoniae on a slide that has been stained using the capsular staining method. however, you do not see capsules surrounding the cells as you expected. what is a likely reason for this? -the slide was over washed with water, rinsing off capsules -the counterstain was not applied for enough time -the slide was heat fixed, which can shrink or destroy capsules -nigrosin was used to stain the background of the slide
the slide was heat fixed, which can shrink or destroy capsules
you are observing Streptococcus pneumoniae on a slide that has been stained using the capsular staining method. however, you do not see capsules surrounding the cells as you expected. what is likely reason for this? -the slide was heat fixed, which can shrink or destroy capsules -the counterstain was not applied for enough time -the slide was over washed with water, rinsing off capsules -nigrosin was used to stain the background of the slide
the slide was heat fixed, which can shrink or destroy capsules
what is the total magnification of a specimen using the 40x objective? -the total magnification would be 4x -the total magnification would be 400x -the total magnification would be 40x
the total magnification would be 400x
why was one sterile broth inoculated with E. coli and the other was not? -the tube that did not have bacteria added serves as a positive control to ensure that the broth would support the growth of E. coli -the tube that did not have bacteria added serves as a negative control to ensure that the broth and the test tubes are sterile -the tube that did not have bacteria added serves as a negative control to ensure that the broth would support the growth of E. coli
the tube that did not have bacteria added serves as a negative control to ensure that the broth and the test tubes are sterile
unlike the other two graphs, the 3rd graph you made related OD to cfu/ml does not indicate the rate of E. coli growth since it does not include time on either of the axes. what does this graph show and what would be the purpose of creating such a graph?
this is a fixed relationship that should remain constant for E. coli at any temperature.
what is the role of the silica in the spin column?
to bind plasmid DNA and allow salts and other contaminants pass through the wash
the role of the NaOH in the lysis buffer is:
to denature the DNA
why is it important to completely sterilize your loop between specimens?
to prevent cross contamination
of the following methods for genetic transfer, which is the only one that would be inhibited by DNase? -transformation -conjugation -transduction
transformation
https://learn-us-east-1-prod-fleet02-xythos.content.blackboardcdn.com/5c1270dbb5a74/14497367?X-Blackboard-Expiration=1615312800000&X-Blackboard-Signature=VK9Ne78Xkxzm7WeaURuRUKk%2B2FGo11TUGFRvIKn1cww%3D&X-Blackboard-Client-Id=100342&response-cache-control=private%2C%20max-age%3D21600&response-content-disposition=inline%3B%20filename%2A%3DUTF-8%27%27SIM%2520tube%2520results.png&response-content-type=image%2Fpng&X-Amz-Algorithm=AWS4-HMAC-SHA256&X-Amz-Date=20210309T120000Z&X-Amz-SignedHeaders=host&X-Amz-Expires=21600&X-Amz-Credential=AKIAZH6WM4PL5SJBSTP6%2F20210309%2Fus-east-1%2Fs3%2Faws4_request&X-Amz-Signature=fb353f272f171213c885beb0023584ad02c32c7876e29b68d33b9456b8a8b0c2 match each tube with the correct description : -sulfate reducer, motile, lacks tryptophanase -non sulfate reducer, motile, expresses trytophanase -non sulfate reducer, motile, lacks tryptophanase -sulfate reducer, motile, expresses tryptophanase -non sulfate reducer, non motile, lacks tryptophanase
tube A --> non sulfate reducer, motile, expresses trytophanase tube B --> non sulfate reducer, non motile, lacks tryptophanase tube C --> sulfate reducer, motile, lacks tryptophanase tube D --> non sulfate reducer, motile, lacks tryptophanase tube E --> sulfate reducer, motile, expresses tryptophanase
creating a bacterial smear from the solid media, such as an agar plate or slant, often feels more tangible than creating a smear from liquid media. which of the following is appropriate when creating a smear in this fashion? -you can place a big lump of bacterial sample onto the slide to ensure the smear is as concentrated as possible -the tip of a gloved finger can be used to mix the bacteria and water on the surface of the slide -using the loop, you should disperse the bacterial sample material into a water drop on the slide
using the loop, you should disperse the bacterial sample material into a water drop on the slide
why is it important that bacterial transformation be tightly controlled in their natural environment?
when bacteria take up random pieces of DNA from the environment, they take a risk because the DNA could potentially be damaging to the cells. they therefore tend to induce competence only under stressful conditions when change within a population is beneficial
sometimes bacteria are grown on agar and sometimes in a liquid broth. how does your protocol differ when making a bacterial smear on a slide if you use one versus the other?
when you make a smear of liquid broth, you put a couple loops of the liquid bacteria directly on a slide, spread it out and leave it to dry. however, if you are working with bacteria growing on agar, you first need to add a couple loops of water onto the slide and then add a small amount of the bacteria into the water. you should then use your loop to mix the bacteria into the water to make a smooth and even mixture
