Exam 1 Objectives 3

Question 1

differentiate positive and negative stains

Answer 1

negative stains the background rather than the actual bacterium, uses nigrosin and no heat fixing

Question 2

identify two common negative stains

Answer 2

congo red and nigrosin(india ink)

Question 3

explain how a negative stain interacts with bacteria and the result obtained

Answer 3

the negative stain uses a dye solution in which the chromogen is acidic and carries a negative charge. The negative charge on the bacterial surface repels the negatively charged chromogen so the cell remains unstained against a colored background

Question 4

understand why slides prepared with negative stains are not heat fixed

Answer 4

they are too delicate to withstand heat fixing, the morphology would be destroyed and size would shrink immensely

Question 5

identify two reasons for using negative stain

Answer 5

to determine morphology and cellular arrangement in bacteria that re too delicate to withstand heat fixing and avoid distorting the cell

Question 6

understand the meaning of draw the medium and do not push it when making negative stained slides

Answer 6

gently draw a second slide across the surface of the first until it contacts the drop so that the drop will spread across the edge of the top slide; push the top slide to the left along the entire surface of the bottom slide

Question 7

know what a bacterial capsule is and how to demonstrate its presence by staining

Answer 7

excreted by cell to form clear, gelatinous, protective layer

background will appear darker(negative stain) then a clear barrier surrounding the stained cell

Question 8

list two common used for poured plates

Answer 8

for streak plates: isolation of microbes to identify and create a pure culture and to create a uniform lawn
often used for isolating individual species form a mixed culture
counting the number of cells in a diluted sample

Question 9

understand the process of preparing and storing stock cultures

Answer 9

take a sample from old stock and spread onto new slant using sterile inoculating loop and store at 25-35 C depending on organism to be grown
do not tighten cap all the way

Question 10

describe the process of preparing sterile plates

Answer 10

use sterile agar broth, famed at the mouth of the tube right after opening, poured with the petri plate lid only slightly open and quickly closed, flame the empty tube and screw back on the lid

Question 11

why when preparing plated media it would be useful to incubate the plates before using them

Answer 11

if the plate has been refrigerated this will prevent cold sensitive bacteria from shock or death, will evaporate any excess condensation on the media (make sure they are sterile and have no growth)

Question 12

identify common sources of contaminants when preparing plated media

Answer 12

air and the lip of tube

Question 13

contains two or more species of microbes

Answer 13

mixed culture

Question 14

contains a single species

Answer 14

pure culture

Question 15

explain why a microbiologist would need pure cultures

Answer 15

in the identification process of an unknown microbe-relies on obtaining a pure culture of that organism
-the streak plate method produces individual colonies on an agar plate then a portion of an isolated colony then may be transferred to a sterile medium to start a pure culture

Question 16

understand why plates are labeled on the bottom of the dish and inverted for incubation and storage

Answer 16

to avoid condensation disturbance of growth as well as rehydrate bacterial colonies

Question 17

decreasing quantity

Answer 17

concentration gradient

Question 18

growth of culture over entire surface of media (individual colonies are indistinguishable)

Answer 18

confluent growth

Question 19

method in streak plating to obtain a pure culture petri dish is labeled on the bottom 4 quadrants

Answer 19

quadrant method

Question 20

sample being introduced to sterile culture media

Answer 20

inoculum

Question 21

tube with solidified agar perpendicular to opening as opposed to the slant
used to study gas requirements of microbes

Answer 21

agar deep

Question 22

a macroscopically visible cluster of identical microorganisms

Answer 22

colony

Question 23

this encompasses colonies that may arise from an individual cell, a pair of cells, chains, or clusters

Answer 23

CFU

Question 24

goal for preparing a streak plate and method for preparing a plate

Answer 24

sterilized inoculation loop used to drug bacterial sample through four quadrants for the purpose of isolating individual or pure cultures

Question 25

give the goal for preparing spread plates and describe how they are made

Answer 25

swab used to create a uniform lawn of bacteria for the purpose of seeing response to certain treatments

Question 26

what are the assumptions and limitations with these procedures

Answer 26

assumption-colonies can be isolated or an even lawn can be made
limitation-due to technique

Question 27

identify uses for streak plates and spread plates

Answer 27

streak- method of bacterial isolation

spread-used for antibiotic and disinfectant testing

Question 28

understand factors that will affect the size of colonies on plates

Answer 28

technique, nutrients, waste products, and antibiotics

Question 29

what is the purpose for using agar in biological media

Answer 29

it is gel at room temp and most microbial species cannot break it down for food. it provides a growing matrix for microbial species through microscopic channels that allow nutrients to diffuse through as food for microbes

Question 30

what is agar used for

Answer 30

to solidfy media for growing organisms, does not feed microbes, nutrients must be added

Question 31

describe how the probable size of an inoculum will affect the way in which a streak plate will be prepared

Answer 31

large inoculum would need larger quadrants and less dips into previous quadrants to spread out colonies more