Lab Exam 3: Selective And Differential Media

Question 1

What is the main resource for identifying the genus and species of a bacteria

Answer 1

Bergey’s Mannual of Systematic bacteriology

Question 2

What growth mediums favor the growth of gram-negative organisms and allow distinctions to be made between types of Graham negative bacteria based on the ability to ferment sugars in the media

Answer 2

EMB and MAC

Both selective and differential

Question 3

What type of medium is mannitol salt auger MSA

Answer 3

Selective and differential. Favors the growth of organisms that can tolerate the 7.5% salt concentration and the ability to ferment mannitol

Question 4

Medium selected for gram-positive bacteria and inhibits most Graham negative bacteria. Should be compared to a control plate

Answer 4

PEA

Question 5

Contains 7.5% sodium chloride and the sugar mannitol and phenol red
Both selective and differential
Yellow =

Answer 5

MSA

Yellow= fermented mannitol

Question 6

Select for Graham negative
Differential for lactose fermentation
PH indicator-turns pink/red when low pH (ferments lactose)

Answer 6

MAC

Question 7

Selective and differential
Inhibits gram-positive bacteria and differentiate based on ability to ferment lactose and or sucrose
Use for isolation of fecal coliform‘s

Answer 7

EMB

Metallic green sheen or dark purple growth indicates lactose fermenter

Growth = gram -

Question 8

Differentiate space on the organisms ability to ferment or oxidize carbohydrates
One out of the two tubes inoculated will be covered with mineral oil to promote anaerobic growth in fermentation
What do the results mean?

Answer 8

Oxidation-fermentation glucose

If both the sealed and unsealed tubes are yellow the organism ferments and oxidizes

If the organism oxidizes only, the medium in the unsealed two will turn yellow while the sealed one will stay green

If the seal tube is green in the unsealed tube is green with blue on top the organism is non-saccharoyltic

Question 9

Broth that contain a single carbohydrate either glucose fructose sucrose lactose or mannitol
And a pH indicator Phenol red

Answer 9

PR broth

Yellow and or gas = fermentor
Bright pink= positive for peptization

Question 10

• this test identifies mix acid from any bacteria it determines if an organism exhibits formic hydrogenase activity
• identifies bacteria capable of fermentation and production of acetone instead of organic acids

Answer 10

MR-VP broth

MR- red on top is positive, yellow is negative

PV- red is positive and yellow is negative

Question 11

Purpleish color on slide indicates positive result

Add 1 to 3 drops of oxidase

Answer 11

Oxidase reaction

Question 12

Gas production and/or red color are positive results

If no color change add zinc.
If it turns red it is negative and yellow is positive

Answer 12

Nitrate reduction

Question 13

-used pH Indicator bromthymol blue
Positive if it turns royal blue
Positive if there is growth but no color change

Answer 13

Simmons citrate agar

Citrate as only carbon source

Question 14

Selective in differential media use on ability to hydrolyzed esculin. Bile inhibits gram-positive organisms except D streptococci enterococi

Answer 14

Bile Esculin Agar (BEA)

If more than half of the tube is dark brown it is positive

Question 15

Test for the presence of amylase.

Answer 15

Start hydrolysis test

If a halo is seen around the bacteria it is positive

Question 16

Used to determine if an organism exhibits urease activity

The enzyme urease converts urea to ammonia and carbon dioxide which will increase the pH of the media

Answer 16

Urea hydrolysis

Pink is positive
Orange is negative

Question 17

The presence of a pink halo around the growth indicating the organism hydrolyzed the DNA into small fragments in nucleotides (toluidine blue)

If (methyl green) is used a positive result is a clear halo

Answer 17

DNA hydrolysis

Question 18

A differential medium that test for the reduction of sulfur, indole production and motility

Answer 18

SIM medium

Blackening of the media is positive for H2S production

Red is positive for indole

Question 19

Tests to determine H2S production

Answer 19

SIM, KIA, or TSI

Question 20

Used to determine anaerobic and aerobic bacteria

Has a phenol red pH indicator

Answer 20

KIA

• Slant and butt red = non-fermenter
• slant is hot pink (P+), butt is yellow =(glucose fermentor but not sucrose or lactose)
• all yellow = ferments lactose and or sucrose, glucose
• Black butt = H2S +

Question 21

Beta hemolysins-
Alpha hemolysins-
Gamma hemolysins-

Answer 21

Beta- completely lyce the red blood cells and a transparent halo around the growth of bacteria

Alpha- only partially degrades, appearance of green to brown pigmented around the bacterial growth

Gamma- growth on the bacteria without any observable change, no hemolysins produce

Question 22

Test use for differentiating gram positive

Clotting indicates a positive result

Answer 22

Coagulase test

Question 23

Test to determine if the bacteria is flagellated

Answer 23

Motility deep

Question 24

What is a positive result for phenylalanine deaminase test?

Answer 24

Dark green color. No color change is negative

Removes amene groups from amino acids

Question 25

Zone > 10 is sensitive

Differentiates beta Group A from resistant B step

Answer 25

Bacitracin

Question 26

Zone > 16 =sensitive

Differentiates coagulase - bacteria

Answer 26

Novobiocin

Question 27

Zone > 14

Differentiates S. Pneumonia

Answer 27

Optochin