Lecture 8 Flashcards

1
Q

Is staphylococcus aureus gram positive or negative?

A

Positive

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2
Q

Is staphylococci motile?

A

No due to a lack of flagella

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3
Q

How do colonies of staphylococci appear?

A

Clusters of spherical cells

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4
Q

What conditions can staphylococci can grow in?

A

resistant to dry conditions and 10% NaCl (Halodurant)

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5
Q

Where is staphylococcus typically found on humans?

A

On the skin typically in warm moist areas such as the armpits, as well in the nasopharynx, oropharynx, GI tract

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6
Q

How does staphylococcus aureus get transmitted?

A

From human to human and through objects as it can survive on dry surfaces through its capsule allowing it to be one of the major hospital acquired infections

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7
Q

What are the two strains of staphylococci aureus?

A

Hospital acquired and Community acquired

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8
Q

What is the difference between community acquired and hospital acquired staphylococcus aureus?

A

Hospital Acquired infections tend to be more resistant through increased antibiotic resistance

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9
Q

What types of antibiotic resistance does staphylococcus aureus possess?

A

Almost all resistant to penicillin, a few stands resistant to methicillin and vancomycin

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10
Q

What provides the resistance to penicillin in staphylococcus aureus?

A

A beta-lactamase gene

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11
Q

What are the two diagnostic tests for staphylococcu aureus?

A
  1. Test for gram +ve
  2. +ve catalase test
  3. +ve coagulase test
    OR
    Appearance of pink bacterium on mannitol salt agar
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12
Q

What virulence factors does staphylococcus aureus posses?

A
Microbial surface components recognising adhesive matrix molecules,
Cytolysins,
Exfoliative toxins
various spreading factors,
Toxic shock syndrome toxin,
Staphylococcal enterotoxin,
Various immune evasion factors
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13
Q

What are microbial surface components recognising adhesive matrix molecules?

A

Cell wall proteins on gram positive bacteria allowing the bacterium to bind to the extracellular matrix

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14
Q

What cytolysins does S. Aureus use?

A

Alpha, Beta, Gamma, Delta and Panton-Valentine leukocidin

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15
Q

What is the function of alpha toxin?

A

To form membrane pores compromising cell membranes killing them

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16
Q

What is the function of beta toxin?

A

Hydrolysis of membrane phospholipids

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17
Q

What is the function of Delta toxin?

A

Detergent like action

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18
Q

What is the function of Gamma and Panton-Valentine leukocidin

A

pore forming toxins

19
Q

What group of toxins is unique to S.Aureus?

A

Exfoliative toxins

20
Q

What is the function of ETA and ETB?

A

Serine proteases that cleave desmosomes causing skine peeling but no inflammation

21
Q

What are the spreading factors of S.Aureus?

A

Lipases, Nucleases, Hyaluronidase, Proteases, Staphylokinase

22
Q

What is the function of Staphylokinase?

A

Fibrinolysis (clot breakdown)

23
Q

What is the function of Hyaluronidase?

A

Hydrolysis of hyaluronic acid in connective tissue

24
Q

What are the super antigens of S.Aureus?

A

Toxic shock syndrome toxin, Staphylococcal enterotoxins

25
Q

What is the function of the superantigens?

A

Trigger large release of pro inflammatory cytokines causing damaging systemic inflammation and potentially food poisoning

26
Q

What are the immune evasion factors of S.Aureus?

A

Capsule, Slime Layer, Catalase, Clumping factor CIF-A, Protein A

27
Q

What is the function of catalase?

A

To reduced the toxic oxidative radicals produced by the immune system to kill the pathogen

28
Q

What is the function of Clumping factor CIF-A?

A

Creates a capsule of fibrin around the cell resulting in a disguise from phagocytosis and oponisation

29
Q

What is the function of Protein A?

A

Bind to Fc regions of antibodies handcuffing them to prevent their functions

30
Q

What are the diseases caused by S.Aureus?

A

Impetigo, Folliculitis, Boils, Carbuncles, Bacteremia and endocarditis, Osteomyelitis, Septic Arthritis, Staphylococcal Scalded skin syndrome, Pneumonia, Staphylococcal Food poisoning, Toxic shock syndrome

31
Q

What is impetigo?

A

Localised skin infection where a pus filled vesicle is formed, typically affects young children

32
Q

What is Folliculitis?

A

impetigo on hair follicules

33
Q

What is a boil?

A

Painful pus filled nodule

34
Q

What are Carbuncles?

A

Boils that extend beyond the skin and thus can cause systemic disease

35
Q

What is Bacteremia and Endocarditis?

A

Spread of bacteria into blood, and to the heart causing endocarditis and often resulting in damage to endothelial cells through secretory enzymes

36
Q

What is Osteomyelitis?

A

Infection in bone, usually at the tip

37
Q

What is septic arthritis?

A

Infection in the joint space, mainly in children and young adults

38
Q

What is staphylococcal Scalded Skin Syndrome?

A

Blisters on the skin, desquamation of epithelium caused by exfoliative toxins. Most common in new borns or premature babies

39
Q

What is pneumonia?

A

S.Aureus causes necrotising pneumonia through use of cytolytic toxins forming abscess’ in lungs

40
Q

What is staphylococcal food poisoning?

A

Microbial intoxication caused by SEA and SEB lasting for only 24 hours as it is an acute reaction

41
Q

What are the two forms of toxic shock syndrome?

A

Menstrual and non menstrual

42
Q

What is menstrual toxic shock syndrome?

A

Growth of bacteria in bagina caused by prolonged usage of tampons

43
Q

What is non-menstrual toxic shock syndrome?

A

Superantigen producing bacteria grows in a wound

44
Q

What are the key risk factors for S.Aureus caused disease?

A

Presence of foreign body which penetrates the skin, including poor hygiene of hospital staff of supression of native flora and lack of antibodies due to use of antibiotics