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Medical Microbiology > Lecture 7 Staphylococcus > Flashcards

Lecture 7 Staphylococcus Flashcards

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USMLE® Step 1 flashcards Biology 101 flashcards
0
Q

What is the major location for S. aureus

A

In the nasal cavity

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1
Q

What are the 3 major Staph that are pathogens and cause most of the disease?

A

S. aureus
S. epidermidis
S. saprophyticus

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2
Q

Major location for S. epidermidis?

A

Dry skin or epithelium

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3
Q

Major location for S. saprophyticus

A

Mucosa, Moist epithelium

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4
Q

Which of the three Staph organisms are Coagulase +?

A

S. aureus

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5
Q

4 main characteristics of S. aureus

A
  1. Coagulase +
  2. Protein A, many secreted enzymes and toxins
  3. Frequently Drug Resistant (MRSA)
  4. Involved in many illnesses such as Food poisoning, Toxic Shock etc.
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6
Q

4 characteristics of S. epidermidis

A
  1. No Coagulase
  2. Capsule
  3. Frequently drug resistant
  4. Catheter and prosthetic implant infections
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7
Q

2 characteristics of S. saprophyticus

A
  1. No Coagulase

2. Urinary tract infections in young women

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8
Q

What is the #2 cause of UTI’s in women?

A

S. saprophyticus

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9
Q

Does S. aureus have a high carrier rate?

A

Yes, it is found in 20-30% of general population at any one time. Carrier rate is higher in Hospital Personnel

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10
Q

Some isolates of S. aureus have become resistant to almost all antibiotics except what?

A

Vancomycin

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11
Q

Name the 6 virulence factors on S. aureus

A
  1. Fibrin binding proteins on cell wall that help colonize cells and tissues
  2. Protein A
  3. Many enzymes secreted
  4. Cytolytic toxins
  5. Superantigen exotoxins
  6. Catalase +
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12
Q

How is catalase a virulence factor for S. aureus

A

Catalase is able to convert the H2O2 secreted by PMN’s and allow S. aureus to survive

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13
Q

What type of toxin is associated with Scalded Skin Syndrome in children

A

Exfoliative Toxin

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14
Q

How do catalytic toxins work?

A

They lyse most cells, including host defense cells

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15
Q

Superantigens (virulence factor) stimulate cytokine production which produces what two illnesses?

A
  1. ‘True’ Food poisoning

2. Toxic Shock syndrome

16
Q

What is the name of the Superantigen that produces Toxic Shock Syndrome?

A

Toxic Shock Syndrome toxin (TSST-1)

17
Q

How does Protein A work?

A

It binds to the IgG Fc site, this blocks the phagocyte adherence to IgG opsonization

18
Q

How does Coagulase work as a virulence factor

A

produces local fibrin deposition that can act to wall off the infection

19
Q

Difference between secreted coagulase and surface coagulase

A
  • Surface coagulase coats the staph cells with host fibrin, hiding bacterial epitopes and camoflaging itself from immune system
  • Secreted coagulase produces local fibrin deposition that acts as a wall around the bacteria and restrict immune system from entering. This often leads to an abcess
20
Q

What leads to an abcess?

A

When Fibrin is deposited by a bacteria and acts to wall off the bacteria from the body and immune system.

21
Q

Name 3 specific spreading factors

A

Staphylokinase
Lipase
Hyaluronidase

22
Q

4 types of local infection caused by S. aureus

A

Local Skin infections
Deep, localized infections
Acute Endocarditis
Pneumonia

23
Q

Local skin infections may lead to what?

A

Cellulitis and Bacteremia

24
Q

2 examples of Local skin infection

A

Abscesses (boils, carbuncles)

Impetigo

25
Q

3 examples of Deep, localized infections

A

Abscesses of the spleen, liver and kidney
Osteomyelitis
Septic Arthritis

26
Q

Explain Scalded skin syndrome

A

An exfoliative toxin (protease) degrades desmosomes releasing the outer layer of epidermis. Rarely fatal and occurs in small babies

27
Q

Explain ‘True’ Food poisoning

A

Enterotoxins (superantigen) acting directly or indirectly on the GI tract to induce diarrhea and vomiting. Toxin does the poisoning not the bacteria

28
Q

What occurs during the Toxic Shock syndrome

A

Superantigen TSST-1 can be released from a focal infection, most commonly next to a mucosal surface. This toxin activates huge numbers of Th cells and macrophages that release cytokines. This massive release of cytokines causes hypovelemic shock, fever, a skin rash with defoliation, diarrhea and vomiting.

29
Q

What two bacteria are a common and increasingly dangerous cause of nosocomial and iatrogenic infections

A

S. Aureus, S. Epidermidis

30
Q

What is a main way in which antibiotic resistant Staph is proliferated?

A

They are usually encoded by plasmids that are readily shared between species and strains, even between enteric bacteria and Staph.

31
Q

Difference between nosocomial infection and iatrogenic infection

A

Nosocomial: Hospital acquired
Iatrogenic: Doctor acquired

Medical Microbiology (17 decks)

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