Streptococci

Question 1

Streptococci has what gram stain and structure?

Answer 1

Gram positive
Cocci
Chains

Question 2

Streptococci can be grouped using what feature?

Answer 2

Haemolytic behaviour

Question 3

What three groups is streptococci grouped into based on haemolysis?

Answer 3

Alpha haemeolysis
Beta haemolysis
Gamma haemolysis

Question 4

Alpha haemolytic Streptococi is based on __________ breakdown of RBCs

Answer 4

Partial

Question 5

Beta haemolytic Streptococi is based on __________ breakdown of RBCs

Answer 5

Complete

Question 6

Gamma haemolytic Streptococci is based on what?

Answer 6

NOT haemolytic

Non-haemolytic strep.

Question 7

What appearance does alpha haemolytic Strep. have on a blood agar plate?

Answer 7

Wet appearance (due to capsule) 
Green appearance

Question 8

What is Alpha haemolytic Strep. also known as?

Answer 8

Viridans Streptococci “green”

Question 9

Give an example of an alpha haemolytic streptococci

Answer 9

Streptococcus pneumoniae

Question 10

How does beta haemolytic streptococci present on a blood agar plate?

Answer 10

Clear zones around each colony

Question 11

According to Lancefield’s classification system, what does “group A” generally means what?

Answer 11

Streptococci Pyogenes

Question 12

Strep. Pyogenes belongs to which group based on haemolytic characteristics?

Answer 12

Beta- Haemolytic (Complete breakdown of RBCs)

Question 13

Name as many virulence factors for Strep. Pyrogenes are you can and what they do

Answer 13

Hyaluronic acid capsule - inhibits phargocytosis
M protein- inhibits phagocytosis
Adhesins- adherence
Streptolysins O and S- lysis of RBCs
DNases- degrade DNA
Streptococcal pyrogenic exotoxins- stimulate T cells, induce cytokines

Question 14

What infection that peaks in incidence in 5-15 year olds can be caused by streptococcus pyogenes?

Answer 14

Streptococcal pharyngitis

Question 15

What are the clinical features of Streptococcal pharyngitis?

Answer 15

Abrupt onset of sore throat, malaise, fever, headache, lymphoid hyperplasia

Question 16

Should Streptococcal pharyngitis be treated with antibiotics?

Answer 16

No, not if you can help it as it will prevent the development of antibodies against M protein which will protect the patient from future infection

Question 17

Name some complications of Streptococcal pharyngitis

Answer 17

Scarlet Fever 
Peritonsillar abscess / cellulitis 
Reteropharyngeal abscess
Acute rheumatic fever 
Acute post-streptocococcal glomerulonephritis 
Meningitis, brain abscess

Question 18

How can Streptococcal pharyngitis cause Scarlet Fever?

Answer 18

Migration of the streptococcal pyrogenic exotoxin locally or haematogenously

Question 19

Peritonsillar abscess is otherwise known as what?

Answer 19

Quincy

Question 20

What are some of the clinical features of Acute rheumatic fever?
Can this follow from any other infection besides pharyngitis?

Answer 20

Inflammation of the heart, joints, CNS

No!!!

Question 21

Name some infections of the skin causes by Streptococcus pyogenes

Answer 21

Impetigo
Erysipelas
Cellulitis
Necrotising fasciitis

Question 22

Impetigo is the most common cause of what complication?

Answer 22

Acute glomerulonephritis

Question 23

What is erysipelas?

Answer 23

A dermal infection caused by Streptococcus pyogenes with lymphatic involvement

Question 24

What is cellulitis?

Answer 24

An infection of the skin and subcutaneous tissue leading to impaired lymphatic drainage

Question 25

Necrotising fasciitis is an infection of what?

It can be described as “fulminant” what does this mean?

Answer 25

Deeper subcutaneous tissues and fascia

Fulminant means it has a very rapid and severe onset

Question 26

How can deep tissue infection with Streptococcus pyogenes cause Streptococcal toxic chock syndrome?

Answer 26

Infection deep into tissue leads to bacteria entering the blood stream followed by vascular collapse and organ failure due to cytokine release, endothelial damage and DIC