Streptococci Flashcards
What is the histology under microscope?
Gram positive cocci in chains
How to categorise the different Streptococci?
- Haemolysis
- alpha -> optochin sensitive/resistant
- beta -> Lancefield group A-G
- none
How to classify Enterococci?
Gram positive cocci in chains, catalase negative, alpha/beta/non haemolytic, Lancefield group D
Example of Group A BHS
Streptococcus pyogenes
Virulence factors of S.pyogenes
- M proteins
- Erythrogenic toxins
- Streptolysins O - form pores which cause cell death and tissue damage
- Hyaluronidase - enzyme digest hyaluronic acid
- Streptococcus pyogenes exotoxins - antigens trigger polyclonal T-cell activation and cytokine storm
What are the two types of diseases does S.pyogenes cause?
- Suppurative (pus forming)
- Non-suppurative (post infectious sequelae)
What suppurative infections does S.pyogenes cause?
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
How to treat S.pyogenes necrotising fasciitis?
Penicillin + Clindamycin, debridement of wound, IVIG
What causes scarlet fever in S.pyogenes?
Streptococcal pyogenic exotoxins - erythrogenic toxins
What bacteria causes impetigo? How does it spread?
Streptococcus pyogenes, Staphylococcus aureus
Spreads easily via close contacts (outbreaks in contact sports like rugby)
How to treat S.pyogenes toxic shock syndrome?
- IVIG to mop up toxin
- Clindamycin to reduce toxin production
What does S.pyogenes acute rheumatic fever lead to?
Rheumatic heart disease
- damaged heart valves which predispose to infectious endocarditis
How to diagnose S.pyogenes acute rheumatic fever?
Revised Jones Criteria
What antibiotics to prevent S.pyogenes acute rheumatic fever?
Oral penicillin/cephalosporins
What is the Revised Jones Criteria?
J: joints polyarthritis
O: carditis
N: subcutaneous nodules
E: erythema marginatum (rash)
S: Sydenham’s chorea
How to diagnose S.pyogenes?
- Culture and gram stain
- Serology: anti-streptolysin O titres
How to treat S.pyogenes?
Penicillins, cephlasporins, macrolides for penicillin-allergic, vancomycin
Necrotising fasciitis: Penicillin + Clindamycin, IVIG, debridement
Example of Group B BHS
Streptococcus agalactiae
Where is S.agalactiae found in normal flora?
GIT and vaginal carriage 30% of the time
Who is susceptible to S.agalactiae infection?
- Neonates and parturient mothers
- Adults with co-morbidities, diabetes, nosocomial (soft tissue, chronic wounds, bedbound)
How to prevent S.agalactiae infections in neonates?
Prophylactic pencillin given to mothers before births
What does S.agalactiae cause in neonates?
Sepsis
Meningitis
Pneumonia
How to treat S.agalactiae?
Penicillins, cephlasporin, macrolides for penicllin-allergic, vancomycin
What diseases does Group C and Group G BHS cause?
- Pharyngitis
- SSTI
Toxin and post-streptococcal complications are rare
Example of Group D BHS
Streptococcus bovis
What diseases does S.bovis cause?
- Endocarditis
- Associated with bowel cancer
- Hepatobiliary
Where is S.bovis found?
GIT
How to treat S.bovis?
Penicillin, cephlasporin, macrolides for pencillin-allergic, vancomycin
What diseases does Enterococcus cause?
- Endocarditis
- UTI
- Biliary infection
What kind of infection does Enterococcus cause?
Nosocomial
What antibiotic is Enterococcus resistant to?
Vancomycin
Cephlasporin
Amoxicillin
How to treat Enterococcus?
- Linezolid, tigecycline
- Endocarditis: vancomycin + gentamicin
- UTI: ampicillin + gentamicin
What are the 2 AHS?
Streptococcus pneumoniae
Streptococcus Viridans
How does S.pneumoniae grow on and as?
Grow on blood agar as draughtsman colonies
S.pneumoniae is optochin ___
sensitive
What diseases does S.pneumoniae cause?
INVASIVE: Pneumonia, meningitis, septicaemia, endocarditis
NON_INVASIVE: URTI, sinusitis, otitis, conjunctivitis
What are the risk factors for S.pneumoniae?
Age, crowding, alcohol, capsule types, asplenic (functional - sickle cell or splenectomy)
Histology of S.pneumoniae
Gram positive cocci in pairs and chains
What kind of pneumonia does S.pneumoniae cause?
Lobar pneumonia
Bronchopneumonia
(with rust-coloured sputum)
How many capsule types does S.pneumoniae have?
> 90 antigenically distinct capsule types due to differences in capsular polysaccharides
What are the 2 types of Pneumococcal vaccines?
- PPSV 23 (penumococcal polysaccharide)
- poor in very young, given to >65y/o
- T-cell independent response (IgM) - PCV (conjugate vaccines)
- Polysaccharide conjugated to a carrier protein
- Elicits T-cell dependent response with memory (IgG)
- given to babies
Treatment for S.pneumoniae
Meningitis: Empirical vancomycin
Respiratory quinolones, cephlasporins, macrolides for penicillin-allergic, vancomycin, penicillins
How to diagnose S.pneumoniae?
- Sputum gram stain and culture
- Blood gram stain and culture
- Urine antigen detection
What does S.viridans group commonly cause?
Endocarditis affecting heart valves with prior damage
Treatment for S.viridans
Penicillin, cephlasporins, macrolides for penicillin-allergic, vancomycin
