Staphylococci

Question 1

Staphylococcus is a Gram _____ organism

Answer 1

Gram positive

Question 2

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

Answer 2

Catalase test

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

Question 3

Species of staph are differentiated based on their production of _____

Answer 3

Coagulase

Question 4

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

Answer 4

Positive: Staph aureus

Negative: Staph epidermidis/saprophyticus

Question 5

T/F: S. aureus ferments mannitol

Answer 5

TRUE

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

Question 6

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

Answer 6

Protein A binds Fc of IgG

Microcapsule also helps in immunoevasion

Question 7

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

Answer 7

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

Question 8

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

Answer 8

Fibronectin adhesins: Fb3 and Embp

Vitronectin adhesins: AtlE

Collagen adhesins: GehD

Question 9

What virulence factors of S. aureus are superantigens?

Answer 9

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

Question 10

What happens after S. aureus adherence?

Answer 10

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

Question 11

What are the hemolysins secreted by S. aureus?

Answer 11

Alpha-toxin, gamma-toxin, phenol soluble modulins

Question 12

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

Answer 12

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

Question 13

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

Answer 13

Abscess

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

Question 14

A _____ is an abscess into subQ tissue. Tx?

Answer 14

Furuncle

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

Question 15

A _____ consists of multiple contiguous furuncles. Tx?

Answer 15

Carbuncle

Drainage +/- abx therapy depending on severity

Question 16

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

Answer 16

Grey/gold colony

Question 17

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

Answer 17

Hemolysins

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

Question 18

Staph aureus is the lading cause of _____ wound infections

Answer 18

Nosocomial wound infections (particularly coronary bypass wounds)

Question 19

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

Answer 19

Staphylokinase + hyaluronidase

Question 20

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

Answer 20

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

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

Question 21

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

Answer 21

Impetigo

Question 22

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

Answer 22

Dairy products/mayo.

Question 23

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

Answer 23

Vagus nerve endings

Question 24

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

Answer 24

Scalded Skin Syndrome

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

Question 25

Scalded Skin Syndrome is characterized by what three clinical symptoms?

Answer 25

Fever, large bullae, erythematous macular rash.

Question 26

What are two potential complications of Scalded Skin Syndrome?

Answer 26

Secondary infection due to large areas of exposed flesh Electrolyte imbalance from exudation of serous fluid

Question 27

_____ 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?

Answer 27

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

Question 28

Describe the "Trojan Horse" mechanism of dissemination of S. aureus.

Answer 28

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

Question 29

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

Answer 29

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

Question 30

Which Staphylococci cause acute infective endocarditis? Chronic?

Answer 30

Acute: S. aureus Chronic: Coagulase negative staph

Question 31

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

Answer 31

Panton Valentine Leukocidin (PVL)

Question 32

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

Answer 32

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.

Question 33

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

Answer 33

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

Question 34

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

Answer 34

FALSE S. saprophyticus is the second most common cause of UTI

Question 35

How is S. saprophyticus UTI treated?

Answer 35

Amoxicillin or Bactrim/sulfa-trimethoprim

Question 36

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

Answer 36

S. saprophyticus

Question 37

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

Answer 37

S. epidermidis & S. saprophyticus

Question 38

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?

Answer 38

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