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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
What does the TSS clinical picture look like?
Abrupt onset of fever, vomiting, myalgias, diarrhea, confusion, RASH with desquamation of palms and soles, severe Hypotension
26
The Capsules (VF) biological effects are to inhibit what?
inhibits chemotaxis and phagocytosis. also inhibits proliferation of mononuclear cells
27
TSS is associated with staph strains producing TSST-1 in whom?
Menstruating women and Others.
28
SSSS causes what in newborns?
Ritter disease
29
SSSS toxins act where?
they act on the dermis
30
In generalized SSSS toxin, Staph secretes what?
secretes exfoliatin
31
In generalized SSSS toxin, the Nikolsky's sign is that?
Detachment of the skin by rubbing
32
What happens in Localized SSSS toxin?
Bullous impetigo and blistering around an infected area
33
Large painful raised nodules with underlying pus?
Furuncles (boils) in pyogenic infections
34
A coalescence of furuncles with multiple sinuses?
Carbuncle
35
There are numerous types of pyogenic infections, give couple of examples?
- Folliculitis (hair follicles) - Styes (eyelids) - Furuncles (boils) - Carbuncle
36
Physical manifestation of Impetigo?
Begins as vesicular lesion, then changes to a crusty erosion
37
What is cellulitis?
infection of the dermal subcutaneous tissues
38
the most common cause of pyogenic infection in Staph infection is what?
Osteomyelitis (pain in bone, fever, redness, tissue swelling)
39
Painful erythmatous joints with collection of purulent material in joint space?
Septic arthritis
40
Staph infections cause what kinds of pneumonia?
- Aspiration pneumonia - Hematogenous pneumonia - Necrotising pneumonia - Empyema
41
Bacteremia/septicemia?
starts as local infection and spreads to blood
42
Endocarditis characteristics?
Acute infection High mortality rate (50%) Fever, malaise, leukocytosis and heart murmur
43
Coagulase enzyme (VF) acts how?
Differentiate S.aureus (+) from other Staph species (-) | Prevent phagocytosis
44
PV-leukocidin Toxin causes what?
Severe cutaneous and necrotizing pneumonia
45
What is the order for lab diagnosis for Staph infections?
1. Microscopic examination 2. Culture 3. Catalase test 4. Coagulase test 5. Biochemical tests
46
S.aureus is positive for thats tests?
ALL | - Coagulase, B-hemolysis, DNAse test, Mannitol fermentation test
47
S. Epidermidis is positive for what tests?
NONE! it is negative for all tests (coagulase, B-hemolysis, DNAse, mannitol fermentation, etc)
48
What are the drugs of choice for Staph infections?
Nafcillin and Oxacillin
49
For hospital acquired MRSA what is the best choice for treatment?
Vancomysin
50
Whats the best treatment option for VISA/VRSA?
Linezolid or Quinspristin/Daptomycin
51
What happens in VISA/VRSA infections which leads to drug resistance?
Terminal pentapeptide changes from D-ala-D-ala to D-ala-D-lac
52
S.epidermidis mainly causes infection how?
mainly causes infection on "hardware" (IVs, CSF shunts, pacemaker wires, etc) due to BIOFILM
53
the biofilm of S.epidermidis protects it from what?
opsonization and phagocytosis
54
S.epidermidis is the major cause of what?
Major cause of infective Endocarditis (Subacute) - Prosthetic valve Infective Endocarditis
55
S. saprophyticus characteristics?
Coagulase negative Non-hemolytic on blood agar UTI in sexually active females
56
S. sapro is resistant to what?
Novobiocin
57
Catalase positive? Catalase negative?
``` Positive = Staphylococci Negative = Streptococci ```
58
Coagulase positive? Coagulase negative?
``` Positive = S.aureus Negative = S.epidermidis, S.sapro ```
59
Novobiocin sensitive? Novobiocin resistant?
``` Sensitive = S. epidermidis Resistant = S.saprophyticus ```
60
Bullous impetigo caused by S. aureus blistered filled with?
Clear fluid
61
What is the mechanism of action of Exfoliatins?
serine proteases which split desmosomes cell adhesion structures
62
S. Aureus is colonized where in children and adults?
Anterior Nares
63
Common properties of MRSA?
- PV leukocidin toxin | - Susceptibility to most Ab other than Beta-lactams
64
Catalse breaks down what?
breaks down H202 into H20 and (1/2)O2
65
Coagulase converts what to what?
converts fibrinogen to fibrin --> than fibrin bound to organism prevents phagocytosis
66
Necrotising pneumonia caused by Community acquired MRSA has what physical manifestation?
Massive hemoptysis
67
Alpha toxin has a cytolytic activity (pore formation) for RBCs, leukocytes and platelets and is an important mediator in what?
cutaneous and soft tissue infections

Bacteriology (17 decks)

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