CHAPTER 3 GUIDE

Question 1

What are the 3 Isolation techniques?

Answer 1

1. Streak plate method 2. Loop dilution, or pour plate, technique 3. Spread plate technique

Question 2

What is the Streak plate method?

Answer 2

a small droplet of sample is spread with a tool called an inoculating loop over the surface of the medium according to a pattern that gradually thins out the sample and separates the cells spatially over several sections of the plate.

Question 3

What is the Loop dilution, or pour plate, technique?

Answer 3

the sample is inoculated, also with a loop, into a series of cooled but still liquid agar tubes so as to dilute the number of cells in each successive tube in the series.

Question 4

What is the Spread plate technique?

Answer 4

a small volume of liquid from a diluted sample is pipetted onto the surface of the medium and spread around evenly by a sterile spreading tool (sometimes called a “hockey stick”).

Question 5

What are the 7 different types of stains?

Answer 5

1. Gram staining 2. Acid-fast stain 3. Endospore stain (spore stain) 4. Structural stains 5. Structural stains 6. Capsule staining 7. Flagellar staining

Question 6

What is Gram staining?

Answer 6

It is an important diagnostic staining technique for bacteria.

Question 7

What is an Acid-fast stain?

Answer 7

It is another commonly used differential stain. This stain originated as a specific method to detect Mycobacterium tuberculosis in specimens.

Question 8

What is an Endospore stain (spore stain)?

Answer 8

It is similar to the acid-fast method in that a dye is forced by heat into resistant survival cells called spores or endospores formed in response to adverse conditions.

Question 9

What are Structural stains?

Answer 9

They are used to emphasize special cell parts such as capsules, endospores, and flagella that are not revealed by conventional staining methods.

Question 10

What is Capsule staining?

Answer 10

It is a method of observing the microbial capsule, an unstructured protective layer surrounding the cells of some bacteria and fungi.

Question 11

What is Flagellar staining?

Answer 11

It is a method of revealing flagella, the tiny, slender filaments used by bacteria for locomotion.

Question 12

What are the 4 processes of Gram staining?

Answer 12

1. crystal violet (the primary dye) 2. Gram’s iodine (IKI, the mordant) 3. an alcohol rinse (decolorizer) 4. contrasting counterstain?usually, the red dye, safranin.

Question 13

Describe the step by step flow of light through a microscope to create image.

Answer 13

1. Magnification in most microscopes results from a complex interaction between visible light waves and the curvature of the lens. 2. When a beam or ray of light transmitted through air strikes and passes through the convex surface of glass as the bending or change in the angle of the light ray as it passes through a medium such as a lens. 3. When an object is placed a certain distance from the spherical lens and illuminated with light, an optical replica, or image, of it is formed by the refracted light.

Question 14

What are the 5 main parts of a microscope that affect the image?

Answer 14

1. Lamp filter 2. Iris diaphragm 3. Condenser 4. Objective lens 5. Ocular lens

Question 15

What is the purpose of lamp filter in the microscope?

Answer 15

The light formed by the lamp is directed through it.

Question 16

What is the purpose of iris diaphragm in the microscope?

Answer 16

It is the opening before the condenser which receives the light from the lamp filter.

Question 17

What is the purpose of condenser in the microscope?

Answer 17

It gathers the light rays and focuses them into a single point on the specimen.

Question 18

What is the purpose of objective lens in the microscope?

Answer 18

It is where the image is formed.

Question 19

What is the purpose of ocular lens in the microscope?

Answer 19

This is where the image is projected, which forms a final magnification.

Question 20

Why do we need to culture microbes?

Answer 20

In some ways, culturing microbes is analogous to gardening. Cultures are formed by “seeding” tiny plots (media) with microbial cells.

Question 21

Differentiate between magnification and resolution.

Answer 21

Magnification is the ability to make objects appear enlarged while Resolution is the capacity of a microscope lens system to accurately distinguish between two separate entities that lie close to each other

Question 22

Describe how the numerical aperture related to resolution.

Answer 22

The other factor influencing resolution is the numerical aperture (NA), a mathematical constant derived from the physical structure of the lens. This number represents the angle of light produced by refraction and is a measure of the quantity of light gathered by the lens.

Question 23

Describe how the wavelength related to resolution.

Answer 23

The wavelength of light is an important factor in the resolution of a microscope. Shorter wavelengths yield higher resolution. The greatest resolving power in optical microscopy requires near-ultraviolet light, the shortest effective visible imaging wavelength.

Question 24

Why do we use oil for oil immersion lenses?

Answer 24

We need oil immersion lenses to maximize its resolving power. This transmits a continuous cone of light from the condenser to the objective, thereby increasing the amount of light and, consequently, the numerical aperture. Without oil, some of the peripheral light that passes through the specimen is scattered into the air or onto the glass slide; the scattering decreases resolution.

Question 25

What is the difference between a negative stain and a positive stain?

Answer 25

Negative stain is a staining technique that renders the background opaque or colored and leaves the object unstained so that it is outlined as a colorless area while Positive stain is a technique in which dye affixes to a specimen and imparts color to it. It takes advantage of the ready binding of bacterial cells to dyes.

Question 26

What is the difference between simple and differential stains?

Answer 26

Simple stain is a type of positive staining technique that uses a single dye to add color to cells so that they are easier to see while the Differential stain is a technique that utilizes two dyes to distinguish between different microbial groups or cell parts by color reaction.

Question 27

Why can’t a Gram stain be performed on cultures older than 24-48 hours?

Answer 27

Because older in older cells, the cell wall begins to degenerate causing the purple stain to not stay in the cell.

Question 28

Could a Gram stain be used to diagnose the flu? Why or why not?

Answer 28

Yes. Because Gram stain can point to a preliminary cause of infection and in some cases it is possible to begin drug therapy on the basis of this stain. Even today, Gram stain remains an important and unbeatable first tool in diagnosis.

Question 29

What is the difference between a mixed culture and a contaminated culture?

Answer 29

Mixed culture is a container growing two or more different, known species of microbes while Contaminated culture has had contaminants that is any undesirable material or organism.

Question 30

Can you isolate bacteria more easily using liquid or solid media?

Answer 30

It is easier to isolate bacteria using solid media because solid media are advantageous for isolating and culturing bacteria and fungi.

Question 31

What is the difference between enrichment and selective media?

Answer 31

Enrichment media is a nutrient medium supplemented with blood, serum, or some growth factor to promote the multiplication of fastidious microorganism’s while selective media contains one or more agents that inhibit the growth of a certain microbe or microbes.

Question 32

In differential media, what is meant by a differential component?

Answer 32

The differential component refers as variations in colony size or color, in media color changes, or in the formation of gas bubbles and precipitates.