Gram positive bacteria Flashcards

1
Q

How to gram pos and gram neg bac differ?

A

Gram pos = 1 membrane = fuzzy part is (thicker) peptidoglycan layer = retains stain = purple

Gram neg = 2 membranes and thin cell wall between the 2 = perioplasmic space = do not retain stain = pink/red stain

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2
Q

Staphylococcus - coagulase features?

Which is the most important coagulase?

A
  • Coagulase pos or neg
  • = enzyme produced by bac that clots blood plasma - fibrin clot formation around bac may protect from phagocytosis

Most important gram pos coagulase = S.aureus
Coagulase neg in opportunistic infecs

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3
Q

Name staphylococcus’ normal habitat

A

Nose and skin

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4
Q

Staph/aureus - how is it spread? What is MRSA resistant to?

A

Spread by aerosol and touch - people are carriers and shedders
MRSA is resistant to;
- beta-lactams
- gentamicin, erythromycin, tetracycline

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5
Q

Staph.aureus virulence factors?

A

Pore forming toxins
- alpha-haemolysis and panton-valetine leucocidin (PVL) = causes haemorrhagic pneumonia

Protease
- exfoliatin (scalded skin syndrome)

Toxic shock syndrome toxin = stimulates cytokine release

Protein A = surface protein which binds Ig’s in wrong orientation

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6
Q

Staph.aureus associated conditions?

A

Pyogenic - wound infec, abscesses, osteomyelitis, pneumonia, endocarditis

Toxin mediated - toxic shock syndrome, food poisoning, scalded skin syndrome

Coagulase negative - infected implants, endocarditis, septicaemia

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7
Q

Coagulase-negative staphylococci - features of S.epidermidis and S.saprophyticus?

A
S.epidermidis = infecs in debilitated, prostheses, catheters
Ability to form persistent biofilms 
S.saprophyticus - acute cystitis 
- haemagglutinin for adhesion
- urease - kidney stones
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8
Q

Types of streptococcus?

A

Alpha - partial, green

  • e.g. S.intermedius
  • H2O2 reacts with Hb

Beta - complete lysis

  • e.g. S.pyogenes
  • Haemolysins O and S

Non or gamma - no lysis
- e.g. some S.mutans

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9
Q

How are streptococci classified?

A

Haemolysis, lancefielding typing, biochemical properties

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10
Q

What is lancefield grouping (sero-grouping)?

A

Method of grouping catalase negative, coagulase neg bacteria based on bacterial carbohydrate cell surface antigens
Carbohydrate cell surface antigens - Lancefield A-H and K-V
Antiserum added to bac - clumping (white dots) = positive
Group A - S.pyogenes - important pathogen
Group B - S.agalactiae - neonatal infecs

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11
Q

Examples of infecs caused by S.pyogenes?

A
Wound infec = cellulitis
Tonsilitis and pharyngitis 
Otitis media
Impetigo 
Scarlet fever
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12
Q

Complications of S.pyogenes infections?

A

Rheumatic fever;

  • Inflam disease of heart, joints, skin, brain - often follows strep. throat infec
  • Antibody cross reactivity

Glomerulonephritis;
- Inflam disease sometimes following S.pyogenes infec

Assessment of risk estimated from anti-SLO titre

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13
Q

What does Anti-SLO titre stand for ASLO? SLO?

A

ASLO - antibody against SLO
SLO - beta haemolysis
Streptococcal antibodies present in serum = rxn occurs
If ASO titre over 200 = agglutination of latex particles (black)

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14
Q

What are S.pyogenes virulence factors?

A

Surface factors;

  • Capsule - hyaluronic acid (protection)
  • M protein = surface protein (encourages complement degradation)
Exported factors;
Enzymes;
- Hyaluronidase - spreading
- Streptokinase - breaks down clots
- C5a peptidase - reduces chemotaxis
Toxins;
- Streptolysins O and S - binds cholesterol
Erythrogenic toxin - SPeA - exaggerated response
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15
Q

Where is S.pneumoniae a normal commensal?

A

Oro-pharynx - 30% of population

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16
Q

What does S.pneumoniae cause?

A

Pneuomia, otitis media, sinusitis, meningitis

17
Q

Predisposing factors of S.pneumoniae?

A

Impaired mucus trapping
Hypogammaglobulinaemia
Asplenia

18
Q

What are the virulence factors of S.pneumoniae?

A

Capsule;

  • Polysaccharide, antiphagocytic
  • Polyvalent vaccine - 23 types = for >2yr olds at risk of infec

Inflam wall constituents;
- Teichoic acid bound to peptidoglycan

Cytotoxin;
- Pneumolysin

19
Q

What is viridans streptococci? Types? What does it cause?

A

Oral streptococci
Alpha or non-haemolytic
Cause caries and abscesses, deep organ abscesses
Important in endocarditis

20
Q

Name the viridans streptococci important in infective endocarditis?

A

S.sanguinis, S.oralis

21
Q

Which viridans streptococci is the most virulent?

A

Milleri group - S.intermedius, S.anginosus, S.constellatus

22
Q

Signs and symptoms of diptheria?

A

Thick, dirty white/grey/black/green coating in mouth, bull neck

23
Q

How does C.diptheriae spread? C.diptheriae can grow in the presence of..?

A

Spreads via droplets

Grows in the presence of potassium tellurite = selective method for isolating this bac from pts throats)

24
Q

What does C.diptheriae toxin do?

A
Inhibits PS
Toxin recognition (Elek plate)
25
Q

How to prevent diptheria?

A

Vaccination - toxoid (inactivated toxin)

DTP vaccine = inactivated diptheria toxin

26
Q

How to test for s.epidermidis?

A

Coag neg
DNase neg
Gamma haemolytic
Blood agar - white colonies

27
Q

How to test for s.saprophyticus?

A

Coag neg
gamma haemolytic
CLED - pale yellow colonies

28
Q

How to test for S.pneumoniae?

A

Alpha haemolytic

No lancefield antigens

29
Q

How to test for viridans streptococci?

A

Alpha or non-haemolytic

30
Q

How to test for streptococcus pyogenes?

A

Blood agar
Beta haemolytic
Lancefield A

31
Q

How to test for staph.aureaus?

A
Coag positive
NDAse positive - clear zone around colony
Aerobic
Blood agar - golden colonies
Beta haemolytic