Microbiology Lab Quiz

Question 1

Aseptic Techniques

Answer 1

Aseptic technique means using practices and procedures to prevent contamination from pathogens. It involves applying the strictest rules to minimize the risk of infection.

Question 2

Microscopy

Answer 2

Microscopy is the technical field of using microscopes to view samples & objects that cannot be seen with the unaided eye.

Diaphragm: controls how much light rays reaching the condenser.

Condenser: used to collect and focus the light from the illuminator on to the specimen.

Question 3

Protists

Answer 3

Eukaryotes

Algae or Protozoa

Algae: Excavata, Archaeplastida, Chromalveolata

Protozoa: Flagellates, amoeba, ciliates, Apicomplexa

Question 4

Motility Methods

Answer 4

Wet mount: a procedure in which a small amount of a liquid culture is placed on a microscope slide and covered with a
cover slip.

Hanging drop: a cover glass is prepared with a small dab of petroleum jelly (Vaseline) on each corner and a single loopful of a liquid culture in the center. A special slide with a depression in the middle is then placed over the cover glass with the concavity in the slide centered over the drop.

Question 5

Simple Staining

Answer 5

The simple stain is used to determine cell shape, size and arrangements of bacteria. The simple stain is a very simple staining procedure involving a single solution of stain.

Methylene blue, crystal violet, or safranin

Question 6

Gram Staining

Answer 6

Gram stains differentiates between gram negative and gram positive bacteria.

Gram positive: purple
Gram negative: pink

1. Crystal violet
2. Iodine
3. Alcohol
4. Safranin

Question 7

Endospore Staining

Answer 7

The endospore stain is a differential stain used to visualize bacterial endospores.

Vegetative cells: pink
Endospores: green

1. Malachite Green
2. Heat (steam)
3. Water
4. Safranin

Question 8

Acid-fast Staining

Answer 8

The acid-fast stain is a differential stain primarily used to detect members of the genus Mycobacterium.

Positive: pink
Negative: blue

1. Carbolfuschin
2. Heat (steam)
3. Acid alcohol
4. Methylene blue

Question 9

Antimicrobic Sensitivity Testing

Answer 9

A sensitivity analysis is a test that determines the “sensitivity” of bacteria to an antibiotic. It also determines the ability of the drug to kill the bacteria.

Streptomycin
Tetracycline
Erythromycin
Kanamycin
Penicillin
Chloramphenicol

Question 10

DNA Extraction from Bacterial Cells

Answer 10

Genomic DNA extraction is an important part of the process when it comes to studying DNA. Pure DNA, separated from the proteins and fluid of cells, is needed on its own in order to be used for various molecular applications.

Question 11

DNA Profiling

Answer 11

DNA profiling is the process where a specific DNA pattern, called a profile, is obtained from a person or sample of bodily tissue. Even though we are all unique, most of our DNA is actually identical to other people’s DNA. However, specific regions vary highly between people. These regions are called polymorphic.

Question 12

Fluid Thioglycollate Medium

Answer 12

A general purpose, liquid medium used to determine the oxygen requirements of bacterial specimens, fluid thioglycollate is also
commonly used to grow microaerophiles and anaerobes.

Question 13

Mannitol Salt Agar

Answer 13

A solid medium with both selective and differential properties, mannitol salt agar is used for the isolation of staphylococci from a mixed culture of bacteria.

The medium contains the carbohydrate mannitol as a carbon source, 7.5% NaCl as a selective agent, and phenol red to detect the fermentation of mannitol to acidic end products.

Mannitol Fermentation
Positive: Yellow
Negative: Red

Question 14

MacConkey Agar

Answer 14

A medium with both differential and selective properties, MacConkey agar contains bile salts and crystal violet to select for Gram-negative bacteria as well as the carbohydrate lactose and the pH indicator neutral red to differentiate between lactose fermenters and lactose non-fermenters.

Positive: pink
Negative: yellow

E.coli

Question 15

Eosin Methylene Blue Agar

Answer 15

Eosin methylene blue agar is a slightly selective medium for the isolation of Gram-negative enteric bacteria. The medium is also differential.

Lactose-fermenting: blue-black
Non-lactose-fermenting: colorless to amber.

Question 16

Blood Agar

Answer 16

Blood agar is commonly used for cultivating fastidious organisms as well as for observing any hemolytic reactions such as those seen with certain species of Streptococcus.

Alpha: partial
Beta: complete
Gamma: None

Question 17

Triple Sugar Iron Agar

Answer 17

Triple sugar iron agar is a differential medium used to evaluate fermentation of sucrose, glucose, and lactose as well as the production of hydrogen sulfide and/or gas. The medium is most often used to help identify Gram-negative rods, such as members of the Enterobacteriaceae.

Ferment sugar: yellow
Non-fermenting: Red
H2S gas: black
Oxygen: Air production

Question 18

Catalase Test

Answer 18

The catalase test detects the presence of the enzyme catalase, which catalyzes the breakdown of hydrogen peroxide to water and oxygen gas.

Question 19

Gelatinase Test

Answer 19

The gelatinase test is used to differentiate those organisms that can enzymatically liquefy gelatin from those that cannot. After an incubation of up to 7 days, the tubes are refrigerated, and those that fail to solidify are considered gelatinase positive; those that solidify upon cooling are gelatinase negative.