Exam 2 (Ch. 3 Staining)

Question 1

preparing a smear (3 steps)

Answer 1

1. aseptically, a thin film of a specimen is spread on a slide
2. film is air dried
3. heat fix

Question 2

staining (def.)

Answer 2

procedures that use dyes to add color to microbes or cellular structures

Question 3

dyes (def.)

Answer 3

chemicals added to microbes

Question 4

name 2 types of dyes

Answer 4

basic dyes and acidic dyes

Question 5

basic dyes (def. and ex.)

Answer 5

have positively charged ions that help them adhere to negatively charged bacteria, ex: crystal violet, methylene blue, safranin and malachite green

Question 6

acidic dyes (2 things and ex.)

Answer 6

1. have negatively charged ions that are attracted to background
2. bacteria appear colorless against a stained background
   ex: nigrosin

Question 7

simple stain (2 things)

Answer 7

1. uses one dye

2. determines cell shapes and arrangements

Question 8

differential stain

Answer 8

places bacteria into categories

Question 9

special stain (def. and ex.)

Answer 9

stains specific parts of microbes, ex: Endospore stain, Negative stain and flagellar stain

Question 10

color of gram positive

Answer 10

purple

Question 11

color of gram negative stain

Answer 11

red

Question 12

ex. of gram positive bacteria

Answer 12

Bacillus

Question 13

ex. of gram negative bacteria

Answer 13

E. coli

Question 14

reason for being gram positive

Answer 14

thick walls of peptidoglycan that retain the primary stain

Question 15

reason for being gram negative

Answer 15

thin wals of peptidoglycan that allow decolorization

Question 16

color of acid fast positive

Answer 16

bright pink

Question 17

color of acid fast negative

Answer 17

blue

Question 18

ex. of acid fast positive

Answer 18

Mycobacterium tuberculosis

Question 19

reasons for acid fast results

Answer 19

1. some bacteria contain a waxy material called mycolic acid in their cell walls which makes staining difficult
2. once heat and carbolfuchsin are applied, acid alcohol does not decolorize the bacteria and they appear red
3. if the bacteria doesn’t contain mycolic acid, carbolfuchsin is decolorized with acid alcohol and methylene blue adheres

Question 20

if spores are present they will appear

Answer 20

green

Question 21

spores can be inside or______ the cell

Answer 21

outside

Question 22

for a spore stain, the bacteria cell will appear what color

Answer 22

red

Question 23

name the two bacteria that produce spores

Answer 23

Bacillus and Clostridium

Question 24

reasons for spore results (3 things)

Answer 24

1. spores are resistant to mild heat but heating in the microwave allows the spores to open
2. heat causes spores to absorb the primary stain and appear green
3. bacteria cells are decolorized with water and counterstain adheres to cells

Question 25

the negative stain is used to determine the presence of what

Answer 25

capsules

Question 26

capsules (def.)

Answer 26

structures that surround the cell wall

Question 27

if a capsule is present it won’t accept the stain and will appear as ______spots against a _______dark background

Answer 27

light; dark

Question 28

what stain can be used to tell if a bacteria is old or young

Answer 28

spore stain