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CV micro > Staph > Flashcards

Staph Flashcards

1
Q

What do staphylococci look like under the microscope?

A

Gram positive spheres arranged in clusters

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2
Q

What are the three major groups of staph that we are concerned about?

A

S. aureus, S. epidermidis, S. saprophyticus

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3
Q

Where is the peptidoglycan layer in gram negatives?

A

In the periplasmic space (between membranes)

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4
Q

Does treatment with cell-wall active drugs or protein synthesis-active drugs cause more exposure of peptidoglycan to the immune system?

A

Cell wall-active drugs

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5
Q

What is the major toxin associated with gram negatives that can cause shock?

A

Endotoxin (aka lipopolysaccharide, LPS)

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6
Q

What does LPS do with the immune system?

A

It is a very potent TLR agonist

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7
Q

What is the rough equivalent of LPS in gram postives?

A

Teichoic acid and lipoteichoic acid (LTA)

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8
Q

Can lipoteichoic acid cause shock all by itself?

A

No

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9
Q

Can LPS cause shock all by itself?

A

Yes

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10
Q

Why do gram positives have such a thick peptidoglycan layer around the cells?

A

The turgor pressure in the cell is very high (about 300 psi…but he said we don’t have to know numbers)

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11
Q

What is the peptidoglycan layer composed of?

A

N-acetylmuramic acid (NAM) and N-acetylglucosamine (NAG) cross-linked by peptides

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12
Q

Is the cross bridge in peptidoglycan attached to NAM or NAG?

A

NAM

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13
Q

How does penicillin (or other β-lactam ABx) kill gram positives?

A

It prevents cross linking of the peptidoglycan, which makes the cell wall less structurally sound, causing the cell to literally explode because of the high turgor pressure.

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14
Q

How do phage lysins kill gram positives?

A

They lyse the cross-bridges in peptidoglycan (the cut between the NAM and the L-Ala of the pentapeptide)

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15
Q

Do bugs have to be growing for β-lactam ABx to work?

A

yes

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16
Q

Do bugs have to be growing for phage lysins to work?

A

no

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17
Q

What is the specific name of the phage lysin that Dr. Hasty gave us?

A

PlyC

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18
Q

What is the long tail of teichoic acid and lipoteichoic acid made of?

A

Polyglycerol phosphate

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19
Q

How do bacteria partially neutralize all of the phosphate groups in LTA?

A

They add D-alanine, which provides it with a positive charge to balance it out

20
Q

Where is wall teichoic acid attached to the cell?

A

It is attached to one end of a peptide cross bridge (which partially destabilizes the cell wall, so if there is too much TA, the cell might rupture)

21
Q

Pus-filled abcesses

A

Staph aureus

22
Q

Indwelling medical devices

A

Staph epi

23
Q

UTIs

A

Staph sapro

24
Q

What are the oxygen requirements of the staphylococci?

A

Facultative aerobes (prefer low O2)

25
Q

Where does S. aureus frequently colonize?

A

anterior narea, axilla, perineum

26
Q

Where does S. epi colonize? How often?

A

Skin. All the time.

27
Q

Where does S. saprophyticus colonize?

A

GI tract, perineum

28
Q

Which species of staph is the major capsule former?

A

Staph. epidermidis makes so much capsule it’s called slime.

29
Q

What do we call bacteria that cause pus formation?

A

suppurative, pyogenic, or purulent

30
Q

Why are capsules a virulence factor?

A

They mediate adhesion to body surfaces (like microthrombi on heart valves). They protect the bacteria from immune cells. They prevent opsonization. They can prevent antibiotics from reaching the bugs

31
Q

Which types of staph are coagulase positive?

A

Only staph. aureus

32
Q

Which types of staph are catalase positive?

A

All staph are catalase positive

33
Q

Why is catalase a virulence factor?

A

It allows the bugs to degrade the stuff that immune cells use to kill them. It’s a defense mechanism

34
Q

What does coagulase do? What is another name for it?

A

It activates prothrombin, which converts fibrinogen into fibrin. It is also called a clumping factor

35
Q

What are the exotoxins made by S. aureus?

A

α-toxin, PVL (a β-toxin)

36
Q

How does the S. aureus alpha toxin work?

A

It is secreted from the bacteria then forms pores in the human cell membrane. This lets ions enter/leave the cell, killing it.

37
Q

How does PVL toxin work?

A

It is a pore-forming beta toxin.

38
Q

Which type of S. aureus is PVL most common in?

A

MRSA

39
Q

What is the causative bacteria of scalded skin syndrome?

A

S. aureus

40
Q

Which S. aureus cellular product causes scalded skin syndrome?

A

Exfoliatin

41
Q

How does exfoliatin work?

A

It is a protease that degrades demoglein-1, which is a cadherin involved with desmosome formation. So, it causes cells in the skin to fall apart from one another

42
Q

What is the typical demographic for scalded skin syndrome?

A

Kids less than 5 years old

43
Q

How many superantigens does S. aureus have?

A

More than a dozen

44
Q

What is an example of a S. aureus superantigen-mediated disease, and what is the name of the associated toxin?

A

Toxic shock syndrome, toxic shock syndrome toxin-1 (TSST-1).

Or food poisoning – staph. enterotoxin A

45
Q

How do superantigens work?

A

They bridge between MHC class II and Tcell receptors, activating the T cell (this is independent of anything being in the Ag binding cleft of either molecule). They can activate 20% of the total T cell pool in the body, causing massive cytokine release

CV micro (3 decks)

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