L51: Streptococcal Infection And Rheumatic Fever Flashcards
***Classifications of bacteria
Aerobic —> gram +ve / -ve —> cocci / bacilli
Anaerobic —> gram +ve / -ve —> cocci / bacilli
Aerobic gram +ve cocci —> catalase +ve / -ve
catalase +ve —> staphylococcus (clusters)
catalase -ve —> streptococcus (chains) —> Beta / Alpha, Gamma haemolytic
Beta —> Lancefield grouping, Bacitracin susceptibility, Biochemical reaction —> A(pyogenes)B(agalactiae)C,G(dysgalactiae)
Alpha, Gamma —> optochin-sensitive, bile-soluble (S. pneumoniae) / optochin-resistance, bile-insoluble (Viridans strept, S. bovis, Enterococci)
Alpha haemolytic, Beta haemolytic, Gamma haemolytic
Beta haemolytic: complete haemolysis
Alpha haemolytic: partial haemolysis / green
Gamma haemolytic: non-haemolysis
*Streptococcus pyogenes (Group A streptococcus: gram +ve, cocci, catalase -ve, beta-haemolytic)
- Lancefield group A
- Bacitracin sensitive
- PYR +ve (convert pink)
- VP -ve
Virulence:
- Antiphagocytic (M protein, capsule)
- Adhere to epithelial cells (M protein, capsule)
- Invasion (Streptokinase, Hyaluronidase)
- Systemic toxicity (Streptolysin O)
Infection:
- Direct damage
—> local (throat: pharyngitis, skin: cellulitis, soft tissue: necrotising fasciitis)
—> systemic (scarlet fever, toxic shock syndrome, bacteraemia)
- Indirect damage (non-suppurative)
—> immune response (rheumatic fever, glomerulonephritis)
Scarlet fever
- follows pharyngitis
- Day 2 rash: upper chest, diffuse red bluish rash, spread centrifugally
- Facial flushing with perioral pallor
- Pastia’s lines
- Strawberry tongue
- Eosinophilia
Skin + Soft tissue infection by Group A Strept
Epidermis: Impetigo
Dermis + subdermis: Cellulitis, Erysipelas
Underlying soft tissue: Necrotising fasciitis, Myonecrosis
Streptococcal toxic shock syndrome
- Hypotension
- Multiorgan involvement (>=2: liver, renal, ARDS, coagulopathy etc.)
Streptococcal pyrogenic exotoxin:
- SpeA, B, C
- Superantigen
Diagnosis of Group A Strept
- Culture (blood, swab)
- Antigen detection
- Serology (antibody response, anti-streptolysin O titre) NOT useful in acute stage
Treatment of Group A Strept
- Penicillin
2. Linezolid (Toxic shock syndrome - 50s, inhibit protein production)
***Acute rheumatic fever
- Valvular damage due to abnormal immune response to Group A Strept
- Heart failure in young adults
- Sequelae of Pharyngitis / Skin infection
- 3 weeks latency
- repeated episodes of ARF —> Rheumatic Heart Disease
Pathogenesis:
*- Molecular mimicry: similar structure between M protein and Cardiac protein (exaggerated T-cell response)
—> Attack Heart (Carditis), Brain (Chorea), Joint (Arthritis), Skin (SC nodules, Erythema marginatum)
- **Jones Criteria (2 Major / 1 Major + 2 Minor)
1. Major - Carditis (Valvulitis, Myocarditis, Pericarditis)
- Arthritis
- Sydenham’s chorea
- Subcutaneous nodules
- Erythema marginatum
- Minor
- fever
- arthralgia
- raised ESR/CRP
- prolonged PR interval - Supportive evidence
- elevated ASO titre
- positive throat culture
Treatment:
- Penicillin (10 days)
- Anti-inflammatory (aspirin, corticosteroid, bed rest)
- Surgery (mitral regurgitation)
Prevention:
- Hygiene
- Primary prophylaxis with Oral antibiotics (prevent 1st attack, treat pharyngitis)
- Secondary prophylaxis with IM antibiotics (prevent recurrence)
Post-streptococcal glomerulonephritis
- Sequelae of Pharyngitis / Skin infection
- Throat: 1-2 week latency (High ASO titre GN)
- Skin: 4-6 week latency (Low ASO titre GN)
- Oedema
- Haematuria
- Hypertension
- Fever
- Adult may progress to chronic GN
Pathogenesis:
- Molecular mimicry
- immune complex deposition
- streptococcal antigen deposition
Streptococcus agalactiae (Group B: beta-haemolytic)
- Lancefield Group B
- Narrow zone beta-haemolysis
- Bacitracin resistant
- CAMP test positive
- hippurate hydrolysis positive
Infection:
- Neonate/infant (early, late onset, beyond early infancy)
—> bacteraemia (early, late, beyond)
—> pneumonia (early)
—> meningitis (late)
—> local infections (late)
- Adult
—> Pregnancy (UTI, genital tract, post-partum bacteraemia)
—> Non-pregnant (skin/soft tissue, septic arthritis, pneumonia, meningitis)
Risks factors
- DM
- Malignancy
- Liver
- Kidney
- Neurological impairment
- Raw fish consumption
Streptococcus dysgalactiae (Group C/G: beta-haemolytic)
- Lancefield group C/G
- Bacitracin resistant
- PYR -ve (group A: +ve)
- VP -ve (group A: -ve)
Infection:
- Pharyngitis (PSGN but NO rheumatic fever)
- Septic arthritis
- Skin/soft tissue
- Bacteraemia (G»C, underlying malignancy)
Streptococcus anginosus (S. milleri)
- Lancefield group A/C/F/G/none
- Bacitracin resistant
- can be alpha/beta/gamma haemolytic
- PYR -ve
- VP +ve
- Caramel smell
Infection:
- Abscess (dental, brain, liver, lung)
- Endocarditis
- Bacteraemia
Comparison between Group A, CG, Anginosus
Only Group A is Bacitracin sensitive
Group A: PYR +, VP -
Group CG: PYR -, VP -
Group Anginosus: PYR -, VP +
Viridans Streptococci
- Group of different strept (anginosus, mutans, salivarius, mitis, sanguinis)
- alpha/gamma haemolytic
- Optochin insensitive, Bile-insoluble
- Oral flora
Infection:
- dental caries
- endocarditis
- bacteraemia
