Streptococci

Question 1

How do Streptococci grow/appear under microscope?

Answer 1

They grow in chains and some grow in short chains of only two cocci called Diplococci (pnemococci), but certainly NOT in clusters/clumps.

Question 2

What are the three most important human pathogen streps?

Answer 2

1. Strep Pyogenes (Group A strep)
2. Strep Agalactiae (Group B strep)
3. Strep Pneumonia

Question 3

What is the range of severity of strep infections?

Answer 3

They range from the relatively harmless oral strep to the flesh eating group A strep.

Question 4

What type of metabolism is used by Strep? What does this mean?

Answer 4

They are Facultative Anaerobes, which means that it can make ATP by aerobic respiration when O2 is present, but they can switch to fermentation if O2 is not present. (obligate anaerobes would die in the presence of O2)

Question 5

What type of plate is strep frequently grown on? Why?

Answer 5

They are frequently grown on Blood agar plates (BAP) bc the medium is sufficient to satisfy nutritional requirements and you can characterize their hemolytic properties, which is very USEFUL in Dx’ing strep.

Question 6

What type of strep are alpha, beta, or gamma hemolytic?

Answer 6

1. Alpha-hemolytic→green→S pneumo, S viridans
2. Beta→clear→S pyogenes, S agalactiae
3. Gamma→non-hemolytic→S salivarus

Question 7

What are effective ways of characterizing/distinguishing different strep species?

Answer 7

1. BAP→hemolysis is only a partial characterization
2. Serology
3. Their ability to grow in the presence of various substances or their metabolic reactions in specific media
4. Catalase and Oxidase Tests

Question 8

How are Strep characterized by serology? What is serology? What are these strep Ag’s called?

Answer 8

They can be classified according to their surface carbohydrate antigens.
Serology is the rxn of Ab’s against the species-specific Ag’s expressed.
In the case of strep, these Ag’s are called Lancefield Ag’s. And based on the type of Lancefield surface antigen, strep species are divided into groups A thru T.

Question 9

What group and hemolytic type is S pyogenes? What about S agalctiae?

Answer 9

S pyogenes is a Group A Strep (GAS) and Beta-hemolytic.

S Agalactiae is a Group B Strep (GBS) and also beta-hemolytic

Question 10

What strep species are untypable by serology? What hemolytic are they?

Answer 10

S pneumonia and S viridans (mutans, sanguis, mitis, salivarius) are untypable by serology, and they are each Alpha-hemolytic.

Question 11

How are Catalase and Oxidase tests helpful in distinguishing strep?

Answer 11

Strep are Catalase Negative, which distinguishes strep from staph(+).
Strep are also Oxidase Negative, which distinguishes strep from Neisseria(+).