Key Bacteria - Streptococci Flashcards

Question

Explain Hyaluronic acid capsule as a virulence factor of S. pyogenes?

Answer 1

- Inhibits phagocytosis by Neutrophils & macrophages | - Poor immunogen (seem like self) because of its similarity to hyaluronate in humans (a connective tissue)

Answer 2

- Resists phagocytosis by inhibiting activation of alternative complement pathway, on bacterial cell surface

Answer 3

Enzyme which catalyses Dissolution (breakdown) of clots | - through conversion of plasminogen to plasmin

Answer 4

An enzyme which catalyses the degradation of hyaluronic acid in host connective tissue

Answer 5

- Aid Adherence, which is the first step in colonisation/infection Examples of adhesins: - M protein - Fibronectin-binding Protein - lipoteichoic acid

Answer 6

- Cleaves Ig G bound to Group A strep. | - Member of superantigenic Spe family (clonal T-cell proliferation)

Answer 7

``` It can be either non-invasive (not spread into the bloodstream) Or Invasive (spread into the bloodstream and to other body sites) ``` - Streptococcal pharyngitis - Complications of Streptococcal pharyngitis - Suppurative complications of Strep pharyngitis - Strep. pyogenes skin infections - Streptococcal toxic shock syndrome

Answer 8

Streptococcal pharyngitis — (A.k.a. Strep throat) • Peak incidence of both resp. & skin infections = 5-15 years old * Person to person droplet spread (associated with overcrowding) * clinical features — - Abrupt onset soar throat - Malaise, fever, headache - Lymphoid hyperplasia - Tonsillopharyngeal exudates (throat pus) * Untreated patients develop M protein specific antibody * Complications — - Scarlet fever - Acute rheumatic fever - Acute post-streptococcal glomerulonephritis - Suppurative complications

Answer 9

Due to infection with Strep. Pyrogenic exotoxins strain of S. pyogenes Spread = can be Local or Haematogenous (carried by blood) Clinical presentation = - High fever - sepsis - arthritis - jaundice - red patches on skin / in armpits

Answer 10

- Peritonsillar cellulitis/abscess - Retropharyngeal abscess - Mastoiditis / Sinusitis / Otitis media - Meningitis, Brain abscess

Answer 11

- Not direct complication of infection. But as a result of the immune reaction to the infection - Inflammation of heart, joints & CNS - Follows on from pharyngitis - Rheumatogenic M types Possible mechanism — ARF can arise due to: - Auto-immune - M protein binding to collagen - Serum sickness = hypersensitivity reaction that results from the injection of heterologous or foreign protein or serum.

Answer 12

- Not a direct complication of infection. But as a result of the immune reaction to the infection - Acute inflammation of renal glomerulus - Due to the formation of antigen-antibody complexes in the glomerulus - M types specific, but not the same as ARF M types.

Answer 13

- Impetigo - Erysipelas - Cellulitis - Necrotising fasciitis

Answer 14

# Define = Skin infection by Streptococcus pyogenes (group A beta-haemolytic streptococcus) Incidence = Often occurs in children aged 2-5yrs Cause = involves Initial skin colonisation, followed by intradermal innoculation Progression = - Impetigo = most common cause of glomerulonephritis

Answer 15

# Define = Skin infection by Streptococcus pyogenes (group A beta-haemolytic streptococcus) Cause = The dermis of the face and/or lower limbs is infected with lymphatic involvement Presentation = Usually affects face or lower limb — - Facial lesions frequently preceded by pharyngitis - Lower limb infection usually secondary to invasion of skin (via trauma, skin disease or local fungal infection)

Answer 16

# Define = skin and subcutaneous tissue infection by Group A Beta-haemolytic Streptococcus (Strep. pyogenes) Risk factors = - impaired lymphatic drainage - illicit injecting drug use Presentation = usually on lower limb, and usually on one limb (almost never on both legs) - occurs mainly in the elderly

Answer 17

Cause = Infection of deep tissue & blood by Strep pyogenes Clinical Progression = (patient can go from healthy to dead in hrs) ``` —> Deep tissue infection —> Bacteraemia —> Vascular collapse —> Organ failure —> Death ```

Answer 18

Mechanism — 1) Entry of group A strep into deeper tissues and bloodstream 2) Streptococcal pyrogenic exotoxins stimulate T-cells, through binding to MHC class II antigen-presenting cells and V-β region of T-cell receptor 3) Induces monocyte cytokines (TNF-α, IL-1β, IL-6) and lymphokines (TNF-β, IL-2, IFN-γ) 4) M-protein fibrinogen complex formation

Answer 19

# Define = infection of deeper subcutaneous tissue and fascia by Strep. pyogenes - deep infection - even down to deep tissue and can even affect muscle - infection usually secondary to skin break - Rapid extensive necrosis - severe pain, even before gross changes - high fever, fulminant course, high mortality Test = sweep test (using finger)

Answer 20

- Full blood count - CRP - For non-invasive Infections = Rapid Strep Test Throat or nose swab Blood culture (blood agar) — sample from: - throat swab - Pus swab - lesion sample - sputum, blood or CSF Blood agar result = appear clear Histology = gram +ve, cocci in chains Catalase test = catalase negative

Answer 21

Antibiotics (Oral or IVABX - depending on severity) - Penicillin - Amoxicillin - Doxycycline (if Penicillin allergy) - Clarythromycin (if Penicillin resistant) - Superficial skin infections = topical antibiotic ointments - Where the infection has caused a lot of skin damage, for example in cases of necrotising fasciitis, damaged tissue may be removed with surgery