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Bacteriology > Staphylococci > Flashcards

Staphylococci Flashcards

1
Q

Staphylococcus is a Gram _____ organism

A

Gram positive

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2
Q

What test is used to differentiate staph. from strep.?

A

Catalase test

Stain –> Gram + –> Catalase test –> Positive –> Staph

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3
Q

Species of staph are differentiated based on their production of _____

A

Coagulase

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4
Q

What is/are the coagulase positive staph(?) The coagulase negatives?

A

Positive: Staph aureus

Negative: Staph epidermidis/saprophyticus

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5
Q

T/F: S. aureus ferments mannitol

A

TRUE

On mannitol salt agar, S. aureus ferments mannitol, turning it red to yellow.

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6
Q

Which virulence factor of S. aureus binds the Fc region of IgG, preventing opsonization/phagocytosis. Which other factor aids in immunoevasion?

A

Protein A binds Fc of IgG

Microcapsule also helps in immunoevasion

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7
Q

Which virulence factor of S. aureus helps it to invade/spread?

A

Invasins (hyaluronidase, staphylysin, leukocidin, leukotoxin, coagulase, staphylokinase)

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8
Q

Which virulence factor(s) of S. aureus functions as fibronectin adhesins? As vitronectin adhesins? As collagen adhesins?

A

Fibronectin adhesins: Fb3 and Embp

Vitronectin adhesins: AtlE

Collagen adhesins: GehD

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9
Q

What virulence factors of S. aureus are superantigens?

A

TSST, EFT, & SE A-G (enterotoxin)

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10
Q

What happens after S. aureus adherence?

A

Replication/secretion of exotoxins (TSST, EFT, SE-AG)

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11
Q

What are the hemolysins secreted by S. aureus?

A

Alpha-toxin, gamma-toxin, phenol soluble modulins

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12
Q

Which two virulence factors of S. aureus aid in biofilm formation?

A

PIA (polysaccharide interellular adhesin) & Aap (Accumulated associated protein)

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13
Q

A _____ is a collection of pus usually around a hair follicle. Tx?

A

Abscess

Tx: Incise, drain, surgically remove foreign body. Usually no abx given.

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14
Q

A _____ is an abscess into subQ tissue. Tx?

A

Furuncle

Incise, drain, DOXYCYCLINE, mupirocin to nares, bleach baths

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15
Q

A _____ consists of multiple contiguous furuncles. Tx?

A

Carbuncle

Drainage +/- abx therapy depending on severity

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16
Q

On blood agar, S. aureus forms a _____ colony, with possible hemolysis.

A

Grey/gold colony

17
Q

Which S. aureus virulence factor causes tissue damage @ the site of infection?

A

Hemolysins

Alpha-toxin, e.g. is the major pore forming toxin that causes skin necrosis during S. aureus infection

18
Q

Staph aureus is the lading cause of _____ wound infections

A

Nosocomial wound infections (particularly coronary bypass wounds)

19
Q

Which two products of S. aureus help it spread along fascial planes, causing cellulitis?

A

Staphylokinase + hyaluronidase

20
Q

What is the opthalmologic emergency staph aureus can cause? What is its clinical presentation?

A

Corneal ulceration (via alpha/beta/delta/gamma toxins, coagulase, nuclease, lipase, hyaluronidase)

Presentation: Stromal cellular infiltration (pus) + anterior chamber reaction

21
Q

_____ is a skin disorder caused by S. aureus that appears as honey-colored/flaky lesions on the face and around the mouth.

A

Impetigo

22
Q

Staph aureus can cause food poisoning after consumption of _____ products.

A

Dairy products/mayo.

23
Q

In Staph aureus food poisoning, staph enterotoxin stimulates _____ in the stomach.

A

Vagus nerve endings

24
Q

_____ is a condition caused by S. aureus where the skin is lifted and filled with fluid. What is the pathogenesis of this condition?

A

Scalded Skin Syndrome

S. aureus secretes epidermolytic exotoxins (exfoliatin A and B), proteases that destroy desmoglein-1. This causes detachment within the epidermal layer.

25
Q

Scalded Skin Syndrome is characterized by what three clinical symptoms?

A

Fever, large bullae, erythematous macular rash.

26
Q

What are two potential complications of Scalded Skin Syndrome?

A

Secondary infection due to large areas of exposed flesh

Electrolyte imbalance from exudation of serous fluid

27
Q

_____ is a condition caused when S. aureus colonize a tampon, sponge or wound and secrete large amounts of TSST-1. This compound is absorbed and acts as a super-antigen. What are some symptoms of this condition?

A

Toxic Shock Syndrome

Sx: Fever, nausea, vomiting, diarrhea followed by rash and exfoliation. May progress to multiple organ system failure like septic shock.

28
Q

Describe the “Trojan Horse” mechanism of dissemination of S. aureus.

A

S. aureus hijacks a neutrophil during phagocytosis. Inside, it won’t be effectively killed by abx.

29
Q

After hijacking a neutrophil, S. aureus can move to the heart or bone and cause what two conditions?

A

Heart: Infective endocarditis (inflammation of valves/congenital defects)

Bone: Osteomyelitis

30
Q

Which Staphylococci cause acute infective endocarditis? Chronic?

A

Acute: S. aureus

Chronic: Coagulase negative staph

31
Q

Which toxin secreted by S. aureus forms pores in cells that line the alveolar space, allowing fluid to accumulate inside of the tissue?

A

Panton Valentine Leukocidin (PVL)

32
Q

PVL activates _____, causing _____ release. What do these activated cells do?

A

PVL activates PMNs and macrophages causing IL-8 release.

Activated cells go on to destroy the cells lining the alveolar space –> hemorrhage

Reminder: IL-8 (CXCL8) is a chemokine that recruits neutrophils to the tissue.

33
Q

T/F S. epidermidis is coagulase-negative and ferments mannitol.

A

FALSE

While S. epidermidis is coagulase negative, is does NOT ferment mannitol.

34
Q

T/F S. saprophyticus is not known to cause any human disease.

A

FALSE

S. saprophyticus is the second most common cause of UTI

35
Q

How is S. saprophyticus UTI treated?

A

Amoxicillin or Bactrim/sulfa-trimethoprim

36
Q

Which species of Staphylococcus is known for its resistance to Novobiocin?

A

S. saprophyticus

37
Q

Which species of Staphylococcus are coagulase negative and do not ferment mannitol?

A

S. epidermidis & S. saprophyticus

38
Q

S. epidermidis produces a lot of adhesins and proteins that make it stick to plastic. What kind of patients are susceptible to eperdimidis because of this feature?

A

Patients in the ICU (lots of lines, plastic, etc.)

Bacteriology (19 decks)

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