Microbiology -- Chapter 2

Question 1

What are the different types of light microscope?

Answer 1

Bright-field, dark-field, phase-contrast, fluorescence

Question 2

What is “resolution”?

Answer 2

smallest distance two objects can be separated and still be distinguishable

Question 3

How is “total magnification” calculated?

Answer 3

10x ocular X 100x objective = 1000x total magnification

Question 4

Why is oil used at high magnification? (100x magnification total)

Answer 4

minimizes loss of light rays and makes it possible to reach 100x magnification without distortion

Question 5

What is meant by “sample fixation”?

Answer 5

____

Question 6

Whay are samples fixed?

Answer 6

detection and resolution of cells are enhanced

Question 7

What are basic and acidic dyes and how are they different from each other?

Answer 7

Basic dyes are positively chargfed and the surface of most bacteria are negatively-charged

Question 8

What is the simple-staining procedure?

Answer 8

1) place loopful of culture on clean side, 2) spread thin film, 3) air dry, 4) fix cells by addding methanol; air dry, 5) stain with methylene blue for 1 min, 6) wash off with water, 7) blot off with excess water, 8) view under microscope

Question 9

What is differential staining?

Answer 9

staining one kind of cell but not the other; Gram staining

Question 10

What is the Gram stian?

Answer 10

differential stain that differentials Gram-positive from Gram-negative by appearnace. Eukaryotes stian negative (turn pink). First used to distinguish streptoccocus pneumoniae.

Question 11

How is the Gram stain performed? (Steps + reagents)

Answer 11

1) add methanol to fix cells to slide. 2) add crystal-violet (purple) for 1 min, 3) add iodine to bind the stain to the G+ cells 1 min. 4) wash with ethanol to remove stain from G-. 20 sec. 5. Add safranin as a counterstain for 1 min (pink)

Question 12

What are G and G- colors after staining?

Answer 12

G+ —> purple…. G- —> pink

Question 13

What is the acid-fast stain?

Answer 13

stains mycolic acids (tuberculosis and leprosy) becuase they are not decolorize by acidified alcohol, non-acid-fast are coutnerstained methylene blue

Question 14

What important bacterial species might be stained by the acid-fast procedure?

Answer 14

mycolic acids — myobacterium tuberculosis and mybacterium leprosae

Question 15

Describe the “capsule stain”

Answer 15

Capsules are colorless against a staine dbackground, to visualize capsules surrounding bacteria

Question 16

Endospore staining?

Answer 16

bacterial endospore stains one color while vegetative cells is a different color

Question 17

What are 2 bacterial genera that produce endospores?

Answer 17

bacillus & clostridium, bacillus thuringiensis, bacillus antracis, clostridium botulinum

Question 18

What are relative sizes of various cells and molecules?

Answer 18

Glucose 0.5 nm. Protein 5 nm. Virus 50 nm. Bacterium 5,000 nm. Eukaryotic cells are 50,000 nm. Period in textbook is 500,000 nm.

Question 19

What can be visualized with each of the varius types of microscopes that we discussed? How are viruses visualized?

Answer 19

Viruses are detected by electron microscope.