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Streptococci Flashcards

1
Q

What is the histology under microscope?

A

Gram positive cocci in chains

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2
Q

How to categorise the different Streptococci?

A
  1. Haemolysis
    - alpha -> optochin sensitive/resistant
    - beta -> Lancefield group A-G
    - none
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3
Q

How to classify Enterococci?

A

Gram positive cocci in chains, catalase negative, alpha/beta/non haemolytic, Lancefield group D

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4
Q

Example of Group A BHS

A

Streptococcus pyogenes

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5
Q

Virulence factors of S.pyogenes

A
  1. M proteins
  2. Erythrogenic toxins
  3. Streptolysins O - form pores which cause cell death and tissue damage
  4. Hyaluronidase - enzyme digest hyaluronic acid
  5. Streptococcus pyogenes exotoxins - antigens trigger polyclonal T-cell activation and cytokine storm
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6
Q

What are the two types of diseases does S.pyogenes cause?

A
  1. Suppurative (pus forming)
  2. Non-suppurative (post infectious sequelae)
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7
Q

What suppurative infections does S.pyogenes cause?

A

Pharyngitis (sore throat)
- Tonsillitis, quinsy (peritonsillar abscess)
Pneumonia (typical post influenza as super added bacterial infections lead to high death rates in influenza)
SSTI
- Erysipelas, cellulitis
- Severe infection, sepsis/shock/organ failure
- Necrotising fasciitis
Toxic shock syndrome
Scarlet fever (circulating exotoxin usually from pharyngitis)
- Rash
- Pharyngitis
- Strawberry tongue

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8
Q

How to treat S.pyogenes necrotising fasciitis?

A

Penicillin + Clindamycin, debridement of wound, IVIG

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9
Q

What causes scarlet fever in S.pyogenes?

A

Streptococcal pyogenic exotoxins - erythrogenic toxins

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10
Q

What bacteria causes impetigo? How does it spread?

A

Streptococcus pyogenes, Staphylococcus aureus
Spreads easily via close contacts (outbreaks in contact sports like rugby)

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11
Q

How to treat S.pyogenes toxic shock syndrome?

A
  • IVIG to mop up toxin
  • Clindamycin to reduce toxin production
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12
Q

What does S.pyogenes acute rheumatic fever lead to?

A

Rheumatic heart disease
- damaged heart valves which predispose to infectious endocarditis

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13
Q

How to diagnose S.pyogenes acute rheumatic fever?

A

Revised Jones Criteria

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14
Q

What antibiotics to prevent S.pyogenes acute rheumatic fever?

A

Oral penicillin/cephalosporins

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15
Q

What is the Revised Jones Criteria?

A

J: joints polyarthritis
O: carditis
N: subcutaneous nodules
E: erythema marginatum (rash)
S: Sydenham’s chorea

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16
Q

How to diagnose S.pyogenes?

A
  • Culture and gram stain
  • Serology: anti-streptolysin O titres
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17
Q

How to treat S.pyogenes?

A

Penicillins, cephlasporins, macrolides for penicillin-allergic, vancomycin

Necrotising fasciitis: Penicillin + Clindamycin, IVIG, debridement

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18
Q

Example of Group B BHS

A

Streptococcus agalactiae

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19
Q

Where is S.agalactiae found in normal flora?

A

GIT and vaginal carriage 30% of the time

20
Q

Who is susceptible to S.agalactiae infection?

A
  1. Neonates and parturient mothers
  2. Adults with co-morbidities, diabetes, nosocomial (soft tissue, chronic wounds, bedbound)
21
Q

How to prevent S.agalactiae infections in neonates?

A

Prophylactic pencillin given to mothers before births

22
Q

What does S.agalactiae cause in neonates?

A

Sepsis
Meningitis
Pneumonia

23
Q

How to treat S.agalactiae?

A

Penicillins, cephlasporin, macrolides for penicllin-allergic, vancomycin

24
Q

What diseases does Group C and Group G BHS cause?

A
  • Pharyngitis
  • SSTI

Toxin and post-streptococcal complications are rare

25
Example of Group D BHS
Streptococcus bovis
26
What diseases does *S.bovis* cause?
1. Endocarditis 2. Associated with bowel cancer 3. Hepatobiliary
27
Where is *S.bovis* found?
GIT
28
How to treat *S.bovis*?
Penicillin, cephlasporin, macrolides for pencillin-allergic, vancomycin
29
What diseases does *Enterococcus* cause?
1. Endocarditis 2. UTI 3. Biliary infection
30
What kind of infection does *Enterococcus* cause?
Nosocomial
31
What antibiotic is *Enterococcus* resistant to?
Vancomycin Cephlasporin Amoxicillin
32
How to treat *Enterococcus*?
1. Linezolid, tigecycline 2. Endocarditis: vancomycin + gentamicin 3. UTI: ampicillin + gentamicin
33
What are the 2 AHS?
Streptococcus pneumoniae Streptococcus Viridans
34
How does *S.pneumoniae* grow on and as?
Grow on blood agar as draughtsman colonies
35
*S.pneumoniae* is optochin ___
sensitive
36
What diseases does *S.pneumoniae* cause?
INVASIVE: Pneumonia, meningitis, septicaemia, endocarditis NON_INVASIVE: URTI, sinusitis, otitis, conjunctivitis
37
What are the risk factors for *S.pneumoniae*?
Age, crowding, alcohol, capsule types, asplenic (functional - sickle cell or splenectomy)
38
Histology of *S.pneumoniae*
Gram positive cocci in pairs and chains
39
What kind of pneumonia does *S.pneumoniae* cause?
Lobar pneumonia Bronchopneumonia (with rust-coloured sputum)
40
How many capsule types does *S.pneumoniae* have?
>90 antigenically distinct capsule types due to differences in capsular polysaccharides
41
What are the 2 types of Pneumococcal vaccines?
1. PPSV 23 (penumococcal polysaccharide) - poor in very young, given to >65y/o - T-cell independent response (IgM) 2. PCV (conjugate vaccines) - Polysaccharide conjugated to a carrier protein - Elicits T-cell dependent response with memory (IgG) - given to babies
42
Treatment for *S.pneumoniae*
Meningitis: Empirical vancomycin Respiratory quinolones, cephlasporins, macrolides for penicillin-allergic, vancomycin, penicillins
43
How to diagnose *S.pneumoniae*?
* **Sputum gram stain and culture** * Blood gram stain and culture * Urine antigen detection
44
What does *S.viridans* group commonly cause?
Endocarditis affecting heart valves with prior damage
45
Treatment for *S.viridans*
Penicillin, cephlasporins, macrolides for penicillin-allergic, vancomycin

Microbiology - Gram Positive (9 decks)

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