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Microbiology Lab exercise 12- Special Media for Isolating Bacteria

front 1

What are the three types of media for isolating bacteria?

back 1

selective, differential and enrichment

front 2

3 common dilution techniques

back 2

pour plate
spread plate
streak plate

front 3

True or false. Diluting may exclude some bacteria that are low in numbers.

back 3

true
only predominant bacteria may be observed
special media may be used to prevent this

front 4

Enrichment media is used to

back 4

enrich the growth of microbes of in low numbers or that are outcompeted by other bacteria that grow faster.
Nutrients are added to enhance specific microbes growth- desired microbes increase in #; others not affected

front 5

Differential media

back 5

different bacteria will look different on special media plates

front 6

Selective media

back 6

apply substances that inhibit undesired microbes or for bacteria that we want to flourish

front 7

Enrichment Media characteristics:

back 7

Typically broths
contain chemicals that ENHANCE the growth of desired bacteria
other bacteria grow also

front 8

Selective Media characteristics:

back 8

contain chemicals that prevent the growth of unwanted bacteria or microbes without inhibiting growth of desired bacteria or microbes

front 9

Differential media characteristics:

back 9

media used to distinguish one bacterium from another
visual differences as microbes grow

front 10

Nutrient Agar is

back 10

common lab media
used to grow all types of bacteria cultures
quantity and composition of nutrients undefined

front 11

Nutrient agar contains:

back 11

peptone- partially digested protein
salt less than 1%
agar- solidifying agent from algae/ powdered form
distilled or deionized water
sometimes sugar is added

front 12

Mannitol Salt Agar characteristics

back 12

selective and differential
NaCl selective for Staphylococcus
-few other can tolerate the high salt concentration (E-coli can do this sometimes)
Differential:
-mannitol fermenters ---> turns yellow due to acid production
-mannitol non-fermenters ---> no color change of agar

front 13

Mannitol contains-

back 13

mannitol
NaCl (7.5%)
peptone
phenol red
agar

front 14

MSA is selective for?

back 14

salt

front 15

MSA is differential for?

back 15

to differentiate between pathogenic and non-pathogenic staph

front 16

Which staph is pathogenic?

back 16

Staphylococcus aureus

front 17

The MSA plate is selective against

back 17

all bacteria except staph

front 18

What is phenol red?

back 18

pH indicator
yellow pH < 6.8 turns yellow-acidic
Stays red pH 7.4-8.4 stays same
Pink > 8.4

front 19

If the mannitol is yellow

back 19

the staph aureus has metabolized the mannitol creating an acid

front 20

MSA plate:
poor growth or no growth

back 20

organism is inhibited by NaCl and is not Staphylococcus

front 21

MSA plate:
good growth no color change

back 21

Organism is not inhibited by NaCl and is non-pathogenic staph

front 22

MSA plate:
Yellow growth or halo

back 22

organisms produces acid from mannitol fermentation
and is possible Staphylococcus aureus

front 23

MSA plate:
Red growth (no halo)-growing well

back 23

organism does not ferment mannitol
nonpathogenic mannitol

front 24

True or false. Any yellow color is from the metabolizing of the mannitol and creating an acid.

back 24

true

front 25

MSA is a conclusive test or presumptive?

back 25

presumptive

front 26

Mannitol salt fermentation

back 26

Organism metabolizes the mannitol during cellular respiration causes fermentation of the mannitol creating an acid causing a yellowing or halo- converted to acid and Staph aureus break down

front 27

Eosin is a

back 27

negative stain- only stains the background

front 28

Methylene blue is a

back 28

simple stain

front 29

Eosin Methylene Blue (EMB) is

back 29

selective and differential

front 30

EMB is used for the

back 30

isolation of fecal coliforms and differentiate between different coliform bacteria

front 31

EMB is selective for:

back 31

selective against gram (+) - only see gram (-) growing on these plates

front 32

EMB is differential for:

back 32

in sugars coliforms can ferment lactose and are gram (-)they might be other gram (-) on plate but they can't ferment the lactose.
if they ferment lactose it turns pink
do not ferment lactose - no color change

front 33

Coliforms that ferment lactose on EMB turns it

back 33

pink

front 34

True or false. All coliforms are gram (-).

back 34

true

front 35

Which organism ferments lactose aggressively and doesn't turn pink due to the aggressive fermentation but metallic green or black.

back 35

E-coli

front 36

Most coliforms are found in the?

back 36

intestinal tract of humans and animals

front 37

Coliforms are gram (-) or gram (+)

back 37

(-)

front 38

Coliforms belong to the ____________ family.

back 38

Enterobacteriaceae

front 39

True or false coliforms ferment lactose?

back 39

true

front 40

They can survive with or without O2 so they are?

back 40

aerobic or facultative anaerobes

front 41

Coliforms are endospore formers or nonendospore formers?

back 41

nonendospore formers

front 42

Coliforms produce ____ and _____ within 48 hours at 37*C

back 42

gas and acid

front 43

True or false several members are pathogens that cause diarrhea.

back 43

true

front 44

Positive for coliform could be potential_____.

back 44

fecal contamination

front 45

EMB has no ______ ________.

back 45

pH indicator

front 46

EMB plate:
poor growth or no growth

back 46

organism is inhibited by eosin and MB
gram positive

front 47

EMB plate:
Good growth

back 47

organism not inhibited by eosin or MB
gram negative

front 48

EMB plate:
growth is pink

back 48

organism ferments lactose with little acid production
possible coliform

front 49

EMB plate:
growth is dark with or without metallic sheen

back 49

organism ferments lactose and/or sucrose with much acid production
probable coliform

front 50

EMB plate:
growth is colorless (no pink, no dark or metallic sheen)

back 50

organism does not ferment lactose or sucrose
noncoliform

front 51

EMB plate is selective against ________ and differential for _______ and _________.

back 51

gram (+)
diff. between coliform and non-coliform

front 52

MacConkey agar is

back 52

selective and differential

front 53

MC agar is selective

back 53

bile salts and crystal violet against gram (+)
inhibits gram (+)

front 54

MC agar is differential

back 54

differentiate between coliform (lactose fermenters) and non-coliforms (non-lactose fermenters)

front 55

The pH indicator for MCagar is

back 55

neutral red

front 56

In MC agar if there is a drop in pH it turns

back 56

red-pink in color

front 57

MC agar:
poor or no growth

back 57

organism is inhibited by crystal violet/ and or bile salts
gram (+)

front 58

MC agar:
good growth

back 58

organism is not inhibited by bile salts and/or crystal violet
gram negative

front 59

MC agar:
pink to red growth with or without bile precipitate

back 59

organism produces acid from lactose fermentation
probably coliform

front 60

MC agar:
Growth is colorless not red or pink

back 60

organism does not ferment lactose
non-coliform

front 61

The procedure for exercise 12:

back 61

4 different agar plates for the known bacteria: Ps. aeruginosa, staph aureus, staph epidermidis, E-coli
EMB
MC agar
Nutrient
MSA

4 different plates for the unknown bacteria: mixed culture
Section each plate off in 1/4s and streak each one with a different microbe (for each diff. agar)
For the other 4 plates streak the plate with a different microbe

front 62

What is the purpose of peptone in the agar?

back 62

To provide nutrients and agar to the bacteria- it is their source of carbon and nitrogen and to facilitate the culture's growth

front 63

What is the purpose of agar in the media?

back 63

To solidify the bacteria in the media

front 64

What ingredient makes mannitol salt selective?

back 64

salt (NaCl)

front 65

Growth on EMB:
(+)
metallic green
colorless

back 65

E-coli gram
Ps. aeruginosa

front 66

Growth on EMB/MSA
(-)
yellow
white

back 66

Staph aureus
Staph epidermidis

front 67

Nutrient agar that contains vancomycin is

back 67

Agar containing vancomycin will only allow vancomycin-resistant organisms to grow.
selective

front 68

EMB agar that contains sorbitol is

back 68

differential to differentiate ecoli 0157