microbiology quiz 4

Question 1

visualization of bacteria using the light microscope can be difficult. because

Answer 1

they are very small, and are trasnparent/colorless

Question 2

what do we use to help us study bacteria

Answer 2

staining

Question 3

what does staining do

Answer 3

shows great contrast between bacteria and background

Question 4

stains consist of

Answer 4

chromophore

Question 5

chromophore is a

Answer 5

colored ion. and a counter ion to balance charge

Question 6

the chromophore can be positively charge known as a

Answer 6

cationic stain

Question 7

the chromophore can be negatively charge known as a

Answer 7

anionic stain

Question 8

charges in chromopore give

Answer 8

different properties to stain

Question 9

what charge do bacterial cells carry at ph 7

Answer 9

negative

Question 10

what are some cationic stains

Answer 10

methylene blue, crystal violet, carbolfuchsin.

Question 11

what are anionic stains

Answer 11

nigrosin

Question 12

anionic stains dont

Answer 12

stain cells directly but stain background

Question 13

2 types of staining techniques

Answer 13

differential and simle

Question 14

simple stains use only a

Answer 14

single stain and are used for observing characteristics such as
morphological shape (cocci, rods, spirilla), size, and characteristic arrangements (singles,
tetrads, chains)

Question 15

differential stains use

Answer 15

two contrasting stains. This type of staining can be used for separating
organisms into groups (Gram stain, Acid-fast stain) or for visualizing particular structures
(Capsule stain, Spore stain)

Question 16

All staining techniques require the preparation of a _____prior to carrying out the staining

Answer 16

smear

Question 17

Successful
staining of bacteria requires obtaining a suitable ____

Answer 17

smear

Question 18

A good smear will be of appropriate ______
to view individual cells, will withstand the repeated ______ steps involved in the staining procedure,
and the cells will retain their original _______.

Answer 18

thickness;washing;morpholgies

Question 19

slides are

Answer 19

sterile

Question 20

use only _________ for transferring bacterial cultures

Answer 20

flamed loop

Question 21

Broth culture:: Before taking organisms, make sure you____ the culture.

Answer 21

mix.

Question 22

how many loopfulsof glass are suspended are applied directly to glass suface

Answer 22

2-3

Question 23

spread organism over the

Answer 23

glass surface

Question 24

some organisms are difficult to get a good smear from due to the presence of

Answer 24

salt and of medium constituents which interfere with the bacteria ‘sticking’ to the glass slide.

Question 25

solid media

Answer 25

Organisms growing on solid medium must be emulsified in a drop of water so as to make a good smear.

Question 26

to dry the slide

Answer 26

put it on slide drier

Question 27

why do we heat fix smear

Answer 27

without heat fixing the bacterial smear will be washed away during thestaining procedure

Question 28

. During the heat fixing, bacteria. Alternatively, smears can be fixed by passing the slide (after it is dry) over the flame of a Bunsen Burner two or three times. If you cannot touch the slide to your hand you have heated it too long.

Answer 28

coagulated and fixed to the glass slide.

Question 29

To heat fix using the slide dryer leave the slide on the drier for _ minutes after the slide is dry

Answer 29

5

Question 31

let stain sit for how long before pouring out

Answer 31

1-2 min

Question 32

what do you doa fter pouring stain off culture

Answer 32

wash off and blot dry

Question 33

what do you examine the slides under

Answer 33

oil immersion

Question 34

gram stains can be used to differentiate wteen

Answer 34

gram positive and gram negative bacteria

Question 35

The basis of differentiation resides in both _____ and _____ of the cells.

Answer 35

phyisical and chemical

Question 36

The mechanism of the gram stain reaction is still

Answer 36

not known.

Question 37

what are theoies o how staining works

Answer 37

Cell wall of gram positive organisms is composed of a heteropolymer of protein and sugar, called murein which provides a barrier through which the crystal violet-iodine complex cannot pass on decolorization A specific gram positive substrate may exist within cell. All major macromolecules have been implicated (lipids, carbohydrates, proteins, nucleic acids); there is evidence of a crystal violetribonucleic acid-iodine complex in gram positive cells Crystal violet-iodine complex, in gram-positive organisms binds to the magnesium-ribonucleic acid component if the cell wall. The resulting magnesium-RNA-crystal violet-iodine complex is more difficult to remove than the crystal violet-iodine complex.

Question 38

gram stain involves use of four reagents

Answer 38

primary stain-crystal violet mordant- grams iodine Decolorizing agent -organic solvent (alcohol or acetone) Secondary or Counter stain- sefranin

Question 39

sefranin serves to

Answer 39

recolor cells that have lost primary stain after alcoho

Question 40

mordant allows

Answer 40

- solution that forms insoluble complex with the primary stain or allows for better complex formation between dye and target compound .

Question 41

declorizing agent

Answer 41

used to remove primary stain from cell

Question 42

Most important step in the Gram stain is

Answer 42

decolorization

Question 43

Bacteria that do not lose primary stain when treated with decolorizer stain purple are

Answer 43

gram positive

Question 44

Gram ______, lose primary stain after decolorization and after counterstaining appear pink.

Answer 44

negative

Question 45

Gram positive bacteria that are not fixed with ______will lose primary stain and appear Gram negative

Answer 45

mordant

Question 46

if ________ left on too long , Gram positive organisms will lose stain and appear gram negative

Answer 46

decolorizer is left on too long

Question 47

the best gram stains are prepared using fresh cultres less then _____ hours

Answer 47

24

Question 48

As the culture_____, organisms tend to lose viability and ability to retain the primary stain.

Answer 48

ages

Question 49

because of aging this might happen

Answer 49

cells may appear gram variable, with some cells being purple (Gram positive) and others red (

Question 50

Lab Procedure

Answer 50

1.Prepare heat smears 2.place slides on rack and dye with crystal violet for 1 min 3.wash with water o staining rack and drain 4. flood with iodine for 1 min 5. wash with water 6. decolorize (apply acetone) 5-15 seconds 7. wash with water 8. counter stain with sefranin for 30-45 sec 9. wash. 10 blot dry record observation