Biology 250. Sample Questions for Lab Quizzes

Lab Quiz 1:

The total magnification achieved by the combination of the ocular and the oil immersion lens on the microscope you are using in class is: a. 10x b. 40 x c. 1000x d. 900x e. 100x
The point of using the oil with an oil immersion lens is to increase: a. resolution b. magnification c. illumination d. all of the above Explain your answer:
Using only a simple stain, what can you determine about bacteria? (three things)
Give three examples of aseptic technique used in the microbiology laboratory other than handwashing and disinfection of the lab bench.
One purpose of aseptic technique is to prevent contamination of the laboratory environment and personnel. What is the other one?
What are you trying to achieve by doing a streak plate (correctly)?
What does a streak plate enable you to observe about the bacteria that you cannot observe by looking at the bacteria growing on a slant or in a broth?
What are two purposes of heat-fixing a smear before you stain it? (or Why do you heat-fix smears? Give 2 answers.)
Why is oil used with the oil immersion lens?
What does parfocal mean?
Why is it important to use good aseptic technique? Give two examples of aseptic technique.
Why do you incubate and store your culture plates upside down (inverted)?
What is the purpose of doing a 3 section streak plate?

Lab Quiz 2:

Which of the steps/reagents above distinguishes between Gram positive and Gram negative cells?
What cell structure is responsible for the difference in staining detected by the Gram stain procedure?
What would a smear of a mixture of Gram negative and Gram positive organisms look like if the final step were omitted?
What is the purpose of doing a differential stain?
What is the difference between a differential stain and a simple stain?
Why is the Gram stain called a differential stain?
What color is a gram negative organism at the end of a Gram staining procedure? A Gram positive organism?
What is the most important step in the Gram staining procedure? Why?
What is the purpose of the 95% ethanol step in the Gram staining procedure? The Gram’s iodine?
Explain the use of a Durham tube.
In the PR broths you did last week, the pH indicator was ______________________________.
In the presence of acid production, what color does it (the pH ind. above) turn? ________________________.
Gas is detected in PR broths tubes by a ________________________________.
The two major products of carbohydrate catabolism detected in the PR (phenol red) broths are ___ and ___.
On the starch plate, if an organism exhibits a positive reaction, the starch is converted to _______________________. The reagent that must be added to the plate is ________________.
The enzyme that catalyzes this conversion (starch to answer above) is _________________________.
What color should the starch agar plate become (after the addition of iodine) if the organism is starch hydrolysis negative? Positive?
An MR positive organism converts glucose to ______________ that is detected by the methyl red.
The color of a positive reaction for MR should be ____________________.
A VP positive organism converts glucose to __________________. Can this product be detected by a pH indicator? ___________
Before you add reagents to MR or VP tubes, or record results for PR broths, what must you be sure has occurred?
(T or F) An organism normally is not positive for both the MR (methyl red) and VP (Voges-Proskauer) tests.

Lab Quiz 3:

An enzyme converts a _________________________ to a ____________________________.
You inoculate a tryptone broth. After 48 hours incubation, you add _______________ reagent, mix gently, and observe that the reagent layer that forms at the top of the broth is cherry red. This is a positive reaction. It means that the organism possesses the enzyme ________________, which is the enzyme that breaks down tryptophane to produce ________________________ .
The enzyme that hydrolyzes urea is called ____________________.
What color is a positive reaction on a urea slant? ________________________
In a SIM tube, blackening in the butt of the tube indicates _____________ production.
Growth only along the line of the stab in SIM indicates that the organism is ____________. Growth throughout the medium indicates that the organism is ____________.
Give the genus and species for a Gram negative bacillus that we have worked with.
What color does the phenylalanine slant turn after you add the reagent if the reaction is positive?
Explain the reasoning you need to use to identify an unknown using a flow chart like the one supplied to you in class last week. Give specific examples.
Give the genus and species for an organism that is phenylalanine positive and urea positive.
Give the genus and species of a lactose positive organism.
State the class of enzymes which hydrolyze large protein molecules.
What is the waste product of protein in most vertebrates?
What would you find in the liquid of a hydrolyzed gelatin?
What is deamination?
What is the signifigance of deamination in bacteria?

Lab Quiz 4:

How does length of exposure correlate with survival of bacteria after exposure to UV light?
UV light causes ___________-_________________ to form in the DNA of bacteria exposed to it.
These in turn cause _____________________________ that may affect survival of the bacteria.
How would you expect spore formation to affect the survival of bacteria exposed to UV light? Did our class observe this result? Why or why not? (Guess...)
Give the name (correctly spelled and punctuated) for the organism we used in the UV exposure exercise.
Is ultraviolet radiation penetrating or nonpenetrating?
Give one example of where ultraviolet radiation might be used as a sterilizing agent.
What is a zone of inhibition?
Name the agar that is used in the Kirby-Bauer test. Why is this specific agar used?
(T or F) The lowest antibiotic concentration is found in the agar that is closest to the antibiotic disk.
What causes the zone of inhibition to form where it does for each organism?
Given the following measurements and table of standardized results, answer the questions below.: Tetracycline R: 14 or less, I: 15-18, S: 19 or more, Unknown: 17; Chloramphenicol R: 12 or less, I: 13-17, S: 18 or more, Unknown: 8; Bacitracin R: 8 or less, I: 9-12, S: 13 or more, Unknown: 14
Is the organism being tested R, I or S for tetracycline? _____
Is the organism being tested R, I, or S for chloramphenicol? ______
Is the organism being tested R, I, or S for bacitracin? _____
Given the information above, is tetracycline the antibiotic you would choose to treat a patient with an infection caused by this organism? ______ Why or why not?
Which antibiotic would you use to treat a patient with an infection caused by this organism?

Lab Quiz 5:

From your disinfectants handout, name four of the major groups of disinfectants and antiseptics. Give an example used in lab for each group.
From your handout, what are two general targets of action of disinfectants and antiseptics?
Which is generally more sensitive to disinfectants/antiseptics, gram positives or gram negatives?
Which is generally more sensitive to disinfectants/antiseptics, organisms in exponential growth, or those in the stationary phase?
Which is generally more sensitive to disinfectants/antiseptics, Pseudomonas or Escherichia?
What is the difference between a disinfectant and an antiseptic? (or Explain the difference....)
How can you determine if growth inhibition on a plate with Chemical X is bactericidal or bacteriostatic?
What are the Lancefield groupings for streptococci based on? Explain how it works.
You swab your throat and streak a blood agar plate. After incubation, you see several small, circular, translucent colonies surrounded by zones of completely lysed red blood cells. The colonies are catalase negative. You streak another plate to obtain a pure culture, and place optochin and bacitracin disks on a heavily inoculated area. The organism appears to be bacitracin sensitive but optochin resistant. What organism is this most likely to be (correctly spelled and underlined)?
Are there more bacteria found in the lower or upper respiratory tract? Why?
What tests would you do and how would you interpret the results to make a confirmed diagnosis of Staphylococcus aureus, given a gram positive coccus? (five tests possible, minimum three)
The substrate for the catalase test is __________________. The product is ________________.
Fibrinogen is converted to fibrin in a positive ______________________________ test.
A yellow color on a mannitol salt agar plate indicates ________________________________.
Greenish discoloration surrounding colonies on a blood agar plate is a sign of ______________.
In regard to the handwashing exercise, if most of the normal flora found resident on our skin is not harmful, why is it so important to effectively scrub your hands prior to surgery or performing a medical procedure?

Lab Quiz 6:

What is the index case in an epidemic?

Define the following terms: epidemic, pathogen, index case

What was the method of transmission of the “disease” in the epidemiology experiment?

During an epidemic, do all people who contact the infected individual acquire the disease? Explain.

Why did we use Serratia marcescens, which makes a red pigment at room temperature, for the epidemiology experiment?

In the epidemiology experiment, why were there more sector 5’s with red colonies than there were sector 1’s?

Explain the difference between differential and selective media.

How can you distinguish between lactose fermenters and nonlactose fermenters on a Hektoen agar plate?

What should Shigella (or Salmonella)look like on a triple sugar iron agar slant? (mention 4 reactions)

What is the inhibitory (or selective) agent in MacConkey’s agar? What does it inhibit (or select against)?

What is the selective agent found in Hektoen agar?

If you inoculated a SIM deep with an organism that was indole positive, nonmotile, and H2S positive, and incubated in and added reagents, what would the deep look like?

By inoculating a SIM deep, what three properties can you determine about the organism?

Given an organism that grows on an EMB plate, producing dark colonies with a metallic blue-green sheen, what could you infer about its catabolism and probable gram reaction?

Based on last week’s lab, what characteristics do the major pathogenic genera of gastrointestinal tract bacteria share? (two)

Correctly name the three major pathogenic genera of the GI tract that we studied in lab last week.

Most pathogens of the gastrointestinal tract are:

a. anaerobic organisms b. lactose-fermenting organisms c. non-lactose-fermenting organisms

(T or F) Most pathogens of the gastrointestinal tract are lactose-fermenting.

Which one of the fungi you observed was a yeast?

Which one had a polysaccharide capsule?

What dye did you use to stain some of the fungi?

What are germ tubes? Sporangia? Macroconidia? Hyphae?

The tape mount you made showed the filamentous growth and sporangia of what organism?

Which organism accounts for about 90% of all yeasts isolated by the diagnostic laboratory?

Why did you use India ink for one of the fungi? Which one?