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Staphylococcus Flashcards

1
Q

What are the properties of Staphylococcus?

A

Gram positive cocci arranged in grape like clusters and is Catalse Positive

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2
Q

Staphylococcus can grow in a media containing high what?

A

salt concentration

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3
Q

Staphylococcus is an important cause of what kind of infections?

A

hospital acquired infections.

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4
Q

What staph spp. is the main pathogen causing pyogenic infections?

A

S. Aureus

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5
Q

Which staph spp. is found mainly on genitourinary mucous membranes and skin?

A

S. Saprophyticus

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6
Q

Which staph spp. is coagulase positive?

A

S. Aureus

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7
Q

This staph spp. is found on normal skin commensals

A

S. Epidermidis

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8
Q

What is the transmission mechanism of staphylococcus?

A
  • Person to person
  • Contaminated fomites (bed linins, clothing)
  • Hands
  • Sneezing
  • Surgical wounds
  • Canned meat products
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9
Q

What is the most common cause of community-acquired skin and soft tissue infections?

A

MRSA

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10
Q

The severity of the Staphylococcus disease depends on what factors?

A
  • Inoculum size
  • Host immunity
  • Virulence
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11
Q

What is the pathogenesis of staphylococcus spp.?

A
  1. Ability of bacteria to evade phagocytosis
  2. Produce surface proteins that mediate adherence
  3. Production of specific toxins and enzymes
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12
Q

What are the 5 main Staph virulence factors?

A
  1. Capsule
  2. Slime layer
  3. Peptidoglycan
  4. Teichoic acid
  5. PROTEIN A
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13
Q

What does Protein A do?

A

Inhibits antibody mediated clearance by binding IgG-Fc receptors.

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14
Q

What is the biological effects of Teichoic acid?

A

Binds to fibronectin

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15
Q

Is Staphylococcus catalase + or -?

A

Catalase positve

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16
Q

What are some important Toxins and enzymes Staphylococcus secretes?

A

Catalase, Coagulase, B-Lactamase, TSST-1, Panton-Valentine Leukocidin toxin

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17
Q

What toxin is responsible for SSSS (staphylococcus scalded skin syndrome)?

A

Exfoliatins (A & B)

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18
Q

Alpha hemolysins is an important virulence factor where?

A

In skin infections

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19
Q

What do Beta, Gamma, and PV-leukocidin toxin do?

A

Lyse macrophages and neutrophils

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20
Q

Which toxin releases severe cutaneous and pulmonary infections?

A

PV-leukocidin

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21
Q

Which toxins act as superantigens in Staphylococcus infections?

A
  1. Toxic shock syndrome toxin (TSST-1)
  2. Enterotoxin A-E, G-I
  3. Exfoliative Toxin A
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22
Q

How does Staph food poisoning (intoxication) occur?

A

Occurs through ingestion of a preformed enterotoxin (A-E) in food contaminated by human carrier or through contaminated Milk and Cheeses, canned meat products, ice cream, etc.

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23
Q

What are the clinical manifestation of staph food poisoning?

A

Abrupt onset of nausea, vomiting, diarrhea,abdominal pain occurring 2-6 hours after ingestion.

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24
Q

Toxic Shock Syndrome is associated with what?

A

toxigenic staph strains producing TSST-1 or Enterotoxin B

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25
Q

What does the TSS clinical picture look like?

A

Abrupt onset of fever, vomiting, myalgias, diarrhea, confusion, RASH with desquamation of palms and soles, severe Hypotension

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26
Q

The Capsules (VF) biological effects are to inhibit what?

A

inhibits chemotaxis and phagocytosis. also inhibits proliferation of mononuclear cells

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27
Q

TSS is associated with staph strains producing TSST-1 in whom?

A

Menstruating women and Others.

28
Q

SSSS causes what in newborns?

A

Ritter disease

29
Q

SSSS toxins act where?

A

they act on the dermis

30
Q

In generalized SSSS toxin, Staph secretes what?

A

secretes exfoliatin

31
Q

In generalized SSSS toxin, the Nikolsky’s sign is that?

A

Detachment of the skin by rubbing

32
Q

What happens in Localized SSSS toxin?

A

Bullous impetigo and blistering around an infected area

33
Q

Large painful raised nodules with underlying pus?

A

Furuncles (boils) in pyogenic infections

34
Q

A coalescence of furuncles with multiple sinuses?

35
Q

There are numerous types of pyogenic infections, give couple of examples?

A
  • Folliculitis (hair follicles)
  • Styes (eyelids)
  • Furuncles (boils)
  • Carbuncle
36
Q

Physical manifestation of Impetigo?

A

Begins as vesicular lesion, then changes to a crusty erosion

37
Q

What is cellulitis?

A

infection of the dermal subcutaneous tissues

38
Q

the most common cause of pyogenic infection in Staph infection is what?

A

Osteomyelitis (pain in bone, fever, redness, tissue swelling)

39
Q

Painful erythmatous joints with collection of purulent material in joint space?

A

Septic arthritis

40
Q

Staph infections cause what kinds of pneumonia?

A
  • Aspiration pneumonia
  • Hematogenous pneumonia
  • Necrotising pneumonia
  • Empyema
41
Q

Bacteremia/septicemia?

A

starts as local infection and spreads to blood

42
Q

Endocarditis characteristics?

A

Acute infection
High mortality rate (50%)
Fever, malaise, leukocytosis and heart murmur

43
Q

Coagulase enzyme (VF) acts how?

A

Differentiate S.aureus (+) from other Staph species (-)

Prevent phagocytosis

44
Q

PV-leukocidin Toxin causes what?

A

Severe cutaneous and necrotizing pneumonia

45
Q

What is the order for lab diagnosis for Staph infections?

A
  1. Microscopic examination
  2. Culture
  3. Catalase test
  4. Coagulase test
  5. Biochemical tests
46
Q

S.aureus is positive for thats tests?

A

ALL

- Coagulase, B-hemolysis, DNAse test, Mannitol fermentation test

47
Q

S. Epidermidis is positive for what tests?

A

NONE! it is negative for all tests (coagulase, B-hemolysis, DNAse, mannitol fermentation, etc)

48
Q

What are the drugs of choice for Staph infections?

A

Nafcillin and Oxacillin

49
Q

For hospital acquired MRSA what is the best choice for treatment?

A

Vancomysin

50
Q

Whats the best treatment option for VISA/VRSA?

A

Linezolid or Quinspristin/Daptomycin

51
Q

What happens in VISA/VRSA infections which leads to drug resistance?

A

Terminal pentapeptide changes from D-ala-D-ala to D-ala-D-lac

52
Q

S.epidermidis mainly causes infection how?

A

mainly causes infection on “hardware” (IVs, CSF shunts, pacemaker wires, etc) due to BIOFILM

53
Q

the biofilm of S.epidermidis protects it from what?

A

opsonization and phagocytosis

54
Q

S.epidermidis is the major cause of what?

A

Major cause of infective Endocarditis (Subacute) - Prosthetic valve Infective Endocarditis

55
Q

S. saprophyticus characteristics?

A

Coagulase negative
Non-hemolytic on blood agar
UTI in sexually active females

56
Q

S. sapro is resistant to what?

A

Novobiocin

57
Q

Catalase positive? Catalase negative?

A 
Positive = Staphylococci
Negative = Streptococci
58
Q

Coagulase positive? Coagulase negative?

A 
Positive = S.aureus
Negative = S.epidermidis, S.sapro
59
Q

Novobiocin sensitive? Novobiocin resistant?

A 
Sensitive = S. epidermidis
Resistant = S.saprophyticus
60
Q

Bullous impetigo caused by S. aureus blistered filled with?

A

Clear fluid

61
Q

What is the mechanism of action of Exfoliatins?

A

serine proteases which split desmosomes cell adhesion structures

62
Q

S. Aureus is colonized where in children and adults?

A

Anterior Nares

63
Q

Common properties of MRSA?

A
  • PV leukocidin toxin

- Susceptibility to most Ab other than Beta-lactams

64
Q

Catalse breaks down what?

A

breaks down H202 into H20 and (1/2)O2

65
Q

Coagulase converts what to what?

A

converts fibrinogen to fibrin –> than fibrin bound to organism prevents phagocytosis

66
Q

Necrotising pneumonia caused by Community acquired MRSA has what physical manifestation?

A

Massive hemoptysis

67
Q

Alpha toxin has a cytolytic activity (pore formation) for RBCs, leukocytes and platelets and is an important mediator in what?

A

cutaneous and soft tissue infections

Bacteriology (17 decks)

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