Exercise 27; pathogenic cocci

Question 1

what type of media is Mannitol Salt agar?

Answer 1

MSA is selective for all types of Staph but is differential for S. Aureus because it changes the medias color from red to yellow by fermenting the mannitol into sugar acid.

Question 2

What does MSA contain and what is it used to test for?

Answer 2

MSA contains high concentrations of salt, sugar mannitol, a pH indicator phenol red, and sodium chloride and it is used to test for Staph (bacteria that can ferment mannitol)

Question 3

What genus of bacteria is selected to grow on MSA?

Answer 3

Staphylococcus

Question 4

what does a negative result on MSA look like and what does it mean?

Answer 4

Negative result would have growth, but there will be no color change of the media from red to yellow, meaning it is Staph, but not S. Aureus.

Question 5

What does a positive result on MSA look like and what does it mean?

Answer 5

.A positive result would have growth and a change of the media from red to yellow, meaning it is S. Aureus and that the bacteria is fermenting the mannitol to sugar acid.
pH< 6.8= yellow (acidic)
pH 7.4 - 8.4 = red
pH greater than 8.4= pink contains sodium chloride
Sodium chloride selects S. aureus

Question 6

What type of media is blood agar?

Answer 6

enriched and differential
Blood agar contains iron and general nutrients and 5% sheep blood. Differential bc of color change in hemolysis
enriched bc enriched w ingredients to support growth for fastidious organisms

Question 7

What characteristics of the bacteria does blood agar detect?

Answer 7

production of hemolysis. (exotoxins that destroy RBCs)

Question 8

Identify Beta hemolysis and what does it mean?

Answer 8

hemolysin (breaks down hemoglobin completely)

(Strep. pyogens )clears RBCs, create a yellow agar

Question 9

Identify Alpha hemolysis and what does it mean?

Answer 9

hemolysin (partially breaks down hemoglobin, green) (strep. pneumonia and S. viridians)
destroy cell membrane but not hemoglobin

Question 10

Identify Gamma hemolysis and what does it mean?

Answer 10

hemolysin (contains no hemolysins)
no reaction
( S. Salivarius)

Question 11

What type of media is Bile Esculin Azide agar?

Answer 11

selective media that will be used to isolate enteric bacteria that can help hydrolize esculin
ex: enterococcus, Group D strep and certain staph.
Differential by a positive reaction for enterococci (dark brown production) to differentiate the enterococci a salt test broth is used.

Question 12

What does BEA plates contain and what is it used to test for?

Answer 12

media contains sodium ozide inhibits growth of all Gram-

esculin is a glycoside (glucose+fat)

Question 13

What types of bacteria does BEA select against?

Answer 13

Gram-

Question 14

What type of bacteria does BEA select for?

Answer 14

bacteria that hydrolizes esculin

Question 15

What are we specifically growing to get results on the BEA test?

Answer 15

staphylococcus aureus

Question 16

Positive results and a negative result on BEA test and what they mean?

Answer 16

Positive result- growth of bacteria and production of brown/black color
Negative result- same clear/yellow agar

Question 17

How does the enzyme catalase work?

Answer 17

will break down hydrogen peroxide into water plus oxygen.

Question 18

Positive and Negative results and what they mean on catalase test?

Answer 18

positive result- bubbles of oxygen. means bacteria has catalase. common for bacteria that are aerobic or facultative anaerobic