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Micro Specialty > Staphylococcus aureus > Flashcards

Staphylococcus aureus Flashcards

1
Q

Motility:

A

non-motile

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2
Q

Catalase:

A

positive

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3
Q

Gram reaction:

A

gram positive cocci in clusters

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4
Q

Atmosphere requirements:

A

Environmental air. Facultative anaerobe

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5
Q

Areas of the body where SA is a commensal:

A

Skin and mucosal membranes

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6
Q

Which percent of the population is colonized by SA in their nares?

A

20-40%

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7
Q

What are the virulence factors of SA?

A

Capsular polysaccharides and biofilm formation
Adhesins
Unique peptidoglycan cell wall with teichoic and lipoteichoic acids
Protein A
Enzymes
Hemolysin
Leukocidins
Toxin production
Superantigens

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8
Q

Colony morphology:

A

Large, smooth colonies. Some strains are pigmented (golden). Some strains are beta-hemolytic.

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9
Q

What does the polysaccharide capsule of SA do?

A

Promotes adherence to host cells and prosthetic devices. Prevents ingestion by PMNs. Alters the binding of complement.

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10
Q

70-80% of significant isolates belong to one of these two serotypes:

A

Serotype 5 or 8

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11
Q

What is the chemical makeup of peptidoglycan?

A

Cross-linked polymers of N-acetylglucosamine and N-acetylmuramic acid

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12
Q

What do the teichoic and lipoteichoic acids in the peptidoglycan wall do?

A

Help adhere to mucosal surfaces and anchor into cell wall enzymes

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13
Q

Which gene codes Protein A?

A

spa

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14
Q

What does Protein A do?

A

Binds to Fc region of all IgG (except IgG3), von Willebrand Factor, and complement protein C3. In doing so, it interrupts the signaling that occurs to initiate an immune response.

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15
Q

What is clumping factor?

A

Enzyme responsible for binding SA to fibrin and fibrinogen.

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16
Q

What is coagulase?

A

Free or cell bound enzyme. Binds and activates prothrombin, promoting the conversion of fibrinogen to fibrin.

17
Q

What are fibrinolysins?

A

Enzymes that breaks down fibrin clots, allowing SA to infect nearby tissues.

18
Q

What is hyaluronidase?

A

Enzyme that breaks down mucopolysaccharides, allowing SA to invade other tissues.

19
Q

What do the lipases SA has do?

A

Aid in the spread to cutaneous and subcutaneous areas

20
Q

What is alpha-hemolysin?

A

Toxin produced by SA that is responsible for the beta hemolysis around cell growth on SBA. This can cause monocytes, macrophages, lymphocytes, and erythrocytes to lyse.

21
Q

What is beta-hemolysin?

A

Toxin produced by SA that hydrolyzes sphingomyelin. Cytotoxic to monocytes and erythrocyte susceptibility varies between animal species. Responsible for synergistic hemolysis observed in positive CAMP test.

22
Q

What are exfoliatins?

A

Epidermolytic toxins responsible for the clinical presentation of “SSSS.” There are two proteins usually associated with SA. ET-A is carried on a chromosome while ET-B is carried on a plasmid.

23
Q

How long does Staphylococcal food poisoning last?

A

2-8 hours

24
Q

Which enterotoxins are responsible for Staphylococcal food poisoning?

A

A-E, H, and I

25
Q

What are the classic signs of toxic shock syndrome?

A

Fever >102 degrees F, diffuse macular erythroderma, desquamation of palms and feet 1-2 weeks after onset of illness, hypotension <90mmHg, plus the involvement of three or more organ systems

26
Q

How does Staphylococcal bacteremia present?

A

Chills, rigor, fever, small hemorrhagic skin lesions, necrotic ulcers

27
Q

How does Staphylococcal endocarditis present?

A

Janeway lesions, Roth spot, splinter hemorrhages, heart murmur, pericardial effusion.W

28
Q

What are common Staphylococcal skin infections?

A

Folliculitis, impetigo, furuncles, carbuncles, hidradenitis supperativa, mastitis, wound infection, and cellulitis.

29
Q

When does Staphylococcal meningitis occur?

A

Primary: local trauma involving neuro surgery. Secondary due to complicated bacteremia.

30
Q

How does Staphylococcal pneumonia present?

A

Tissue necrosis with cavitation, bacteremia, lung abscesses, pleural empyemas.

31
Q

How does Staphylococcal osteomyelitis occur?

A

Complication of local infection with hematogenous seeding

Micro Specialty (20 decks)

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