Untitled Deck

Question 1

What is the mechanism of bleach (sodium hypochlorite)?

Answer 1

Oxidizes proteins and damages DNA, leading to cell death.

Question 2

What makes Bacillus subtilis resistant to UV and disinfectants?

Answer 2

It forms endospores that resist environmental damage.

Question 3

What type of mutation does UV light cause?

Answer 3

Thymine dimers in DNA.

Question 4

What does ciprofloxacin target?

Answer 4

DNA gyrase, preventing DNA replication.

Question 5

Which antibiotic disrupts bacterial membranes and is effective only on Gram-negative bacteria?

Answer 5

Polymyxin B

Question 6

What is MIC?

Answer 6

Minimum Inhibitory Concentration – the lowest concentration of an antibiotic that prevents bacterial growth.

Question 7

What does a yellow glucose fermentation tube mean?

Answer 7

Acidic byproduct; positive for fermentation.

Question 8

What does bubbling in the catalase test indicate?

Answer 8

Presence of catalase enzyme.

Question 9

What is the differential agent in Mannitol Salt Agar?

Answer 9

Mannitol + phenol red (pH indicator).

Question 10

What is the purpose of EMB agar?

Answer 10

To detect lactose fermentation by Gram-negative bacteria.

Question 11

What does a positive urease test look like?

Answer 11

Bright pink color due to ammonia production.

Question 12

What are the three parts of the SIM test?

Answer 12

Sulfur reduction, Indole production, Motility.

Question 13

What is a plaque in a virus assay?

Answer 13

Clear area where cells have been lysed by viruses.

Question 14

What does ELISA detect?

Answer 14

Presence of a specific antigen (or antibody) via enzyme-linked color change.

Question 15

Why do antigen-antibody complexes stay on the plate during ELISA?

Answer 15

They are bound to the plate through strong interactions.

Question 16

How do you make a 1 M NaCl solution?

Answer 16

Dissolve 58.5 g NaCl in 1 L of water.

Question 17

What’s the formula for diluting solutions?

Answer 17

C₁V₁ = C₂V₂

Question 18

How many grams for 100 mL of a 5% NaCl solution?

Answer 18

5 g

Question 19

How does ethanol kill microbes?

Answer 19

By denaturing proteins and disrupting lipid membranes.

Question 20

Why is 70% ethanol more effective than 100% ethanol?

Answer 20

Water is needed to penetrate cells and slow evaporation, allowing better protein denaturation.

Question 21

What makes hydrogen peroxide a good disinfectant?

Answer 21

It generates reactive oxygen species (ROS) that damage DNA, proteins, and lipids.

Question 22

Which disinfectant is most effective against spores?

Answer 22

Bleach (sodium hypochlorite).

Question 23

What kind of light is used to kill microbes in UV experiments?

Answer 23

UV-C light (~254 nm).

Question 24

What is a thymine dimer?

Answer 24

A bond between two adjacent thymine bases in DNA caused by UV light, disrupting replication.

Question 25

How does Bacillus subtilis survive UV exposure better than E. coli?

Answer 25

It produces endospores with protective coatings.

Question 26

What type of DNA repair can some bacteria perform after UV exposure?

Answer 26

Photoreactivation (using photolyase enzymes to reverse thymine dimers).

Question 27

What class of antibiotic is penicillin and what is its target?

Answer 27

β-lactam; inhibits peptidoglycan synthesis in bacterial cell walls.

Question 28

Which antibiotic inhibits protein synthesis by binding to the 30S subunit?

Answer 28

Streptomycin.

Question 29

Which Gram-negative-specific antibiotic damages the outer membrane?

Answer 29

Polymyxin B.

Question 30

Why don’t all antibiotics work equally on Gram-positive and Gram-negative bacteria?

Answer 30

Differences in cell wall structure—Gram-negatives have an outer membrane.

Question 31

What is the purpose of the coagulase test?

Answer 31

To detect the enzyme coagulase, which clots plasma (Staphylococcus aureus is positive).

Question 32

What does a positive catalase test indicate?

Answer 32

The bacterium produces catalase to break down hydrogen peroxide (bubbles appear).

Question 33

Which agar is both selective and differential for Staphylococcus species?

Answer 33

Mannitol Salt Agar (MSA).

Question 34

What kind of hemolysis causes a clear zone around colonies on blood agar?

Answer 34

Beta-hemolysis (complete lysis of RBCs).

Question 35

What does a metallic green sheen on EMB agar indicate?

Answer 35

Strong lactose fermentation (e.g., E. coli).

Question 36

What does the SIM test check for?

Answer 36

Sulfur reduction, indole production, and motility.

Question 37

What does a red layer after adding Kovac’s reagent in SIM mean?

Answer 37

Positive indole production.

Question 38

What does the MR test detect?

Answer 38

Strong acid production from glucose fermentation (mixed acid pathway).

Question 39

What result indicates positive citrate utilization?

Answer 39

Color change to blue on Simmons citrate agar.

Question 40

What does a pink color in the urease test mean?

Answer 40

Positive urease activity (alkaline pH from ammonia).

Question 41

What does each plaque on an agar plate represent?

Answer 41

A single virus particle that infected and lysed host cells.

Question 42

What is the PFU/mL formula?

Answer 42

(Number of plaques × dilution factor) / volume plated (in mL).

Question 43

What is the difference between the lytic and lysogenic cycles?

Answer 43

Lytic: immediate replication and cell lysis; Lysogenic: viral DNA integrates into host genome.

Question 44

Why is T4 bacteriophage specific to E. coli B?

Answer 44

It recognizes specific surface receptors on that strain only.