Microbio Lab 3

Question 1

pure cultures

Answer 1

contains only a single kind of an organism, whereas a mixed culture contains more than one kind of an organism; can study morphological and physiological characteristics of an individual organism

Question 2

streak plate

Answer 2

physical dilution of cells over the plate surface until a single cell is deposited in an area and grows to produce an isolated bacterial colony (quadrant streak method and radiant streak) Requires more skill but less time and materials

Question 3

pour plate

Answer 3

separating one species of bacteria from another by diluting one loopful of organisms across a series of tubes of liquified nutrient agar in such a way that one of the plates poured will have an optimum number of organisms to provide good isolation requires less technique but requires more time and materials

Question 4

colony

Answer 4

identical progeny of the original cell and can be picked and used for further study of the bacterium

Question 5

simple staining

Answer 5

the use of a single stain to color a bacterial cell (methylene blue, basic fuchsin, and crystal violet)

Question 6

basic dyes

Answer 6

dyes that contain color bearing ionic groups (chromophores) that are positively charged (cationic); stain negative exterior of cell

Question 7

acidic dyes

Answer 7

dyes that have anionic chromophores; repelled by bacterial cells and stain background of slide

Question 8

bacillus

Answer 8

rod shaped cells bacilli, coccobacillus, fusiform

Question 9

cocci

Answer 9

spherical shaped cells diplococci, tetrads, streptococci, staphylococci

Question 10

spirals

Answer 10

corkscrew shaped rods comma, spirillum, spirochaetes

Question 11

fusiform bacteria

Answer 11

rod shaped bacteria with tapered ends

Question 12

pleomorphism

Answer 12

pertains to irregularity of form; demonstrating several different shapes

Question 13

metachromatic granules

Answer 13

distinct reddish-purple granules within cells that show up when the organism are stained with methylene blue; they are masses of volutin, a polymetaphosphate

Question 14

palisade arrangement

Answer 14

parallel arrangement of rod-shaped cells

Question 15

flagella

Answer 15

major organelles of motility in bacteria; allow cells to move toward nutrients in the environment or move away from harmful substances; rigid helical structure

Question 16

chemotaxis

Answer 16

movement toward nutrients or away from harmful substances

Question 17

wet mount

Answer 17

A drop of viable cells is placed on a microscope slide and covered with a cover glass; observed using phase-contrast ; dry out easily

Question 18

hanging drop

Answer 18

a drop of cells is placed on a cover glass, which is then placed over a special slide that has a concave depression in its center; the coverslip is held in place with vaseline and it creates an enclosed chamber which prevents drying

Question 19

Brownian motion

Answer 19

cell movement caused by currents under the glass; movement due to molecular bombardment of cells causing cells to shake or ‘jiggle’ but not move in any specific direction

Question 20

monotrichous

Answer 20

Question 21

lophotrichous

Answer 21

Question 22

peritrichous

Answer 22

Question 23

amphitrichous

Answer 23

Question 24

Robert Koch

Answer 24

Father of medical microbiology; developed isolation methods for obtaining pure cultures of bacteria

Question 25

Define the term “colony” as it relates to bacterial growth on solid media?

Answer 25

A single pure colony is the identical progeny derived from a single cell. One colony is equal to approximately one billion cells.

Question 26

What colony characteristics can be used for differentiation of bacterial species? As an example, compare the properties of colonies of Serratia marcescens and Micrococcus luteus on your streak plate.

Answer 26

Useful colony characteristics for differentiation of bacterial species include size, color, shape, texture, opacity, and odor. For example, Serratia marcescens colonies are red, irregular in shape, and have a strong odor. Micrococcous luteus, on the other hand, are yellow, opaque, round, and dome-shaped.

Question 27

Why is dilution a necessary part of pure culture preparation?

Answer 27

When working with a culture that may contain millions of cells, dilution on a solid medium is essential for separating the cell with enough space so that they can grow into isolated colonies.

Question 28

What advantages does the streak plate method have over the pour plate method?

Answer 28

Streak-plate method is more economical in materials and time.

Question 29

What advantages does the pour plate method have over the streak plate method?

Answer 29

Pour-plate method requires less skill, has optimization built it, and will most likely produce the desired result.

Question 30

Before inoculating and pouring molten nutrient agar into a plate, why must the agar first be cooled to 50 degrees Celsius?

Answer 30

So that microbes added to the medium will not be killed by excessive heat, but it must not be cooled too much because it will solidify before the cells can be dispersed and poured. If too hot when poured, excess moisture will form on the lid of the plate.

Question 31

Explain why plates should be inverted during incubation?

Answer 31

Plates are inverted so that moisture does not accumulate on the lid and drop to the agar surface. This will cause the organisms to spread and negate the dilution effect. Also agar plates tend to dehydrate faster in the upright position.

Question 32

Describe the difference between the appearance of surface and subsurface colonies in a pour plate. Why do these differences occur?

Answer 32

Subsurface colonies are small and embedded in the agar. They do not have the identifying characteristics of surface colonies such as edge, surface characteristics, and in some cases, pigment. Subsurface colonies must grow under limited oxygen conditions, which would affect growth and some characteristics.

Question 33

Flagella structure

Answer 33

A rigid filament that occurs in the form of a helix (constitutes the main part of the flagellum structure). The filament is connected to a hook that is attached to a shaft that is inserted into a series of rings. Gram positive cells possess S & M rings and gram negative cells possess S,M,L, and P rings

Question 34

How do flagella generate motility?

Answer 34

proton motive force (basal body transports protons across cell membrane)

Question 35

Which arrangement of flagella would be more likely to be associated with a highly motile species?

Answer 35

lophotrichous; confirm by looking at how far it travels

Question 36

Differentiate between directional motility, Brownian movement, and water current movement?

Answer 36

Directional motility is movement in random directions, and caused by flagella

Brownian movement is caused by molecular bombardment (jiggling)

Water current movement is movement in the same direction

Question 37

Between wet mounts and hanging drop slide preparations, which is more resistant to evaporation? Which works best with phase-contrast microscopy?

Answer 37

Hanging drop slides are more resistant to evaporation, although wet mount slides work better with phase-contrast microscopy.

Question 38

What concentration of agar is used in a semisolid medium for motility determination? How does that compare to a typical solid medium?

Answer 38

A concentration of 0.4% agar is used to make semisolid media, which when stabbed, allow motile bacteria to swim but hold nonmotile in place. Typical solid medium contains 1.5% agar, which when stabbed, would not allow movement of motile bacteria.

Question 39

Why are semisolid media sometimes preferred over slide techniques for evaluating bacterial motility?

Answer 39

Exposure of individuals to pathogens is more likely when making wet slides as opposed to stabbing a semisolid medium where the bacteria are contained. There are also fewer false positives when using semisolid media because their is no Brownian movement or water current.

Question 40

If SIM medium was used for motility determination for Proteus vulgaris, what noticeable change to the medium was observed?

Answer 40

SIM is a semisolid medium that will not only show motility (M) of P. vulgaris, but also sulfide production (S), which is visualized as a balck precipitate that forms in the medium when H2S complexes with iron salts

Question 41

colony not on streak lines

Answer 41

contamination

Question 42

staphylococcal

Answer 42

cocci in clusters

Question 43

streptococcal

Answer 43

cocci in clusters

Question 44

tetrad

Answer 44

four

Question 45

diplococcus

Answer 45

pairs

Question 46

motility test

Answer 46

Use semisolid media (0.3 or 0.4% vs 1.5% agar-allows motile bacteria to move through agar)

Contains tetrazolium dye that turns red when there is growth