Beta-haemolytic Streptococci

Question 1

How is streptococci classified in regards to haemolysis?

Answer 1

Alpha haemolysis (partial break down, viridans, green),

beta-haemolysis (full breakdown, pyogenes, pus),

gamma non-haemolytic (no breakdown, enterococcus faecalis)

Question 2

Structurally how can streptococci be classified?

Answer 2

G +ve cocci, chains, non-motile, coag –ve, Ag classification schemes A-F

Question 3

What are the virulence factors of streptococci pyogenes

Answer 3

Capsule = protects bacteria from Ab/complement,
M protein = res to phagocytosis,
adhesins = helps adhere, streptolysins = lysis of RBCs neutrophils platelets,
DNAses = degrades DNA,
hyaluronidase =degrades hyaluronic acid in CT,
streptokinase = plasminogen to plasmin,
exotoxins = cleaves IgG

Question 4

List the main clinical infections caused by streptococci pyogenes

Answer 4

Strep pharyngitis = abrupt sore throat, malaise, fever, headache, lymph hyperplasia, tonsil exudates.

Impetigo = skin colonisation, intradermal.

Erysipelas = dermal infection.

Cellulitis = skin, subcutaneous infect.

Necrotising fasciitis = subcutaneous, fascia, very rapid – extensive necrosis

Question 5

What is streptococcal toxic shock syndrome?

Answer 5

due to group A strep, Low BP, multiple organ failure, exotoxins stimulate massive nonspecific T cell activation = cytokines and lymphokines

Question 6

What can be the complications of strep pharyngitis?

Answer 6

Scarlet fever (fever, sepsis, arthritis, jaundice),

acute rheumatic fever (inflam of heart, joints, CNS),

acute post-strep glomerulonephritis (acute inflam renal glomerulus)

Question 7

Outline appropriate management

Answer 7

Not acquired resistance to penicillin G, penicillin allergy = clarithromycin, clindamycin is added to penicillin to inhibit toxin production = stop sudden release from dying bacteria