Streptococcus

Question 1

What is the structure of streptococci?

Answer 1

Gram positive
Cocci
Chains (varying in length)

Question 2

How can streptococci be classified by haemolysis?

Answer 2

Alpha- partial breakdown of rbc, green on agar (viridans)

Beta- complete breakdown of rbc

Non-haemolytic

Question 3

What’s an example of alpha haemolysis step?

Answer 3

Strep pneumoniae

Question 4

What’s an example of beta haemolysis strep?

Answer 4

Step pyrogens (pus producing)

Question 5

What’s an example of non-haemolytic strep?

Answer 5

Enctococcus faecalis

Question 6

How is strep classified by Lancefield?

Answer 6

Via the serology of beta-haemolytic

Based on cell wall antigens
Divided into groups eg, A,B,C ect..

Question 7

What group to streptococcus pyrogens belong to?

Answer 7

Group A (lancefield) beta haemolytic

Question 8

What are the main virulence factors in strep pyrogens?

Answer 8

Hyaluronic acid capsule- similar to human connective tissue

M protein- surface protein that resists phagocytosis

Enzymes- from lysis of rbc to degradation of DNA

Pyrogenic exotoxins- cleaves IgG bound to group A strep

Question 9

What is strep pharyngitis?

Answer 9

Caused by strep pyrogens

Sore throat, malaise, fever, headache
Lymphoid hyperplasia
Tonsilliopharygeal exudates (swollen and pussy)

Develop own antibodies against M protein

Question 10

What is scarlet fever?

Answer 10

Complication of step pharygenitis

Causes local/ haematogenous spread

Fever, sepsis, arthritis, jaundice

Question 11

What are suppurative complications of strep pharyngitis?

Answer 11

Pus complications

Burst abscesses can lead to bread of infection down via lateral pharyngeal space of up into brain ect

Question 12

What is actuate rheumatic fever?

Answer 12

Complication of strep pharyngitis

Inflammation of heart, joints and CNS
Possibly an auto-immune cause due to M protein

Can be prevented with early antibiotics

Question 13

How does actuate rheumatic fever develop?

Answer 13

Have a group A strep throat infection

If right type of M protein will get an immunological reaction at a later time

This causes a cross reaction with native antigens in heart/ CNS ect

At time of fever don’t have infection

Question 14

What is actuate post strep glomerulonepritis?

Answer 14

Inflammation of renal glomerulus

Due to different M protein to that that causes ARF

Due to antibody-antigen complexes

Question 15

What skin infections doe strep pyrogens cause?

Answer 15

Impetigo- common in childhood, can cause glomeruonphritis

Erysipelas-dermis infection involving lymphatics

Cellulitis- skin and subcutaneous tissue, impaired lymph drainage

Necrotising fasciitis- deeper subcutaneous tissue and fascia, rapid onset, severe pain, mortality

Question 16

What is strep toxic shock syndrome?

Answer 16

Deep disuse infection with strep pyrogens with

Blood stream infections
Lowered bp
Organ failure

Question 17

How does toxic shock develop?

Answer 17

Group A strep into blood stream

Pyrogenic exotoxins stimulate population activation of T cells
Mass activation of cytokines ect

Sepsis like response