B4.068 Staphylococcus Aureus

Question 1

pyogenic

Answer 1

pus forming

Question 2

common gram neg pyogenic bacteria

Answer 2

Neisseria
E.coli
pseudomonas aeruginosa

Question 3

common gram pos pyogenic bacteria

Answer 3

strep pyogenes
staph aureus (80% of pus forming infections)

Question 4

suppuration

Answer 4

formation of pus

Question 5

what is pus

Answer 5

mixture of living and dead neutrophils, bacteria, and cellular debris
usually forms in an area of persistent infection

Question 6

abscess

Answer 6

circumscribed collection of pus
relatively inaccessible to antibodies and antibiotics
may have to be drained to relieve pressure or to resolve infections

Question 7

preliminary immune response to pyogenic bacteria

Answer 7

activation of macrophages and other innate immune cells
chemotactic factors produced by resident cells to mount and acute phase response
activation of adaptive immunity and Th17 cells
acute inflammation (neutrophil infiltration, production of lysosomal enzymes)

Question 8

how does an abscess form?

Answer 8

inflammatory area contained within a thick walled fibrous cap
from the hosts point of view, it has contained the invading organism

Question 9

describe the overarching features of staph aureus

Answer 9

gram pos coccus
grow in irregular grapelike clusters
nonmotile, non spore forming
catalase positive
coagulase positive

Question 10

why is the coccus shape important?

Answer 10

highly resistant shape/size
can survive:
high temp
high salt concentrations
drying

Question 11

how does staph aureus react on blood agar

Answer 11

colonies are golden
strongly hemolytic
B hemolytic

Question 12

how many individuals in the US are colonized with s. aureus?

Answer 12

as many as 80%
most only intermittently
20-30% colonized persistently

Question 13

who has high rates of colonization?

Answer 13

health care workers
persons with diabetes
patients on dialysis

Question 14

main site of colonization

Answer 14

anterior nares

Question 15

other sites of colonization

Answer 15

axilla
rectum
perineum
vaginal (higher during menses)

Question 16

what can happen after abscess formation with s. aureus?

Answer 16

organisms can disseminate hematogenously

largely due to bacterial proteolytic enzymes

Question 17

what are some signs of s. aureus dissemination?

Answer 17

pneumonia, bone and joint infections, infection of heart valves

pneumonia: infants, young children, debilitated
endocarditis: janeway lesions, oslers nodes, roth’s spots

Question 18

mortality rate of untreated s. aureus

Answer 18

80%

Question 19

mortality rate of staph TSS

Answer 19

3-5%

Question 20

TSS diagnostic criteria

Answer 20

fever 102 or higher
rash resembling scarlet fever
desquamation of skin 1-2 weeks after onset
hypotension
clinical/lab abnormalities in 3 organ systems

Question 21

what cell type is a major player against staph aureus

Answer 21

neutrophils

Question 22

what is the difference between colonization and non-colonization pathways

Answer 22

colonization: ClfB binding, micro-invasion, upregulation of IL-10
non-colonization: bacterial clearance rather than ClfB binding, upregulation of IL-17, neutrophil infiltration

Question 23

what is ClfB and what opposes it?

Answer 23

clumping factor B, allows for adhesion

hBD-3 = human B-defensing 3 blocks binding

Question 24

most common cause of septicemia following surgical procedures

Answer 24

staph aureus

Question 25

common pathology of MRSA

Answer 25

mild to severe skin infections resulting in death if not treated promptly

Question 26

common manifestations of staph infections

Answer 26

skin (folliculitis, furuncles/carbuncles, impetigo) wound scalded skin syndrome

Question 27

folliculitis

Answer 27

tender pustule involving a hair follicle

Question 28

furuncle

Answer 28

small abscess that exudes purulent material from a single opening

Question 29

carbuncle

Answer 29

aggregate of furuncles with several openings

Question 30

septic arthritis

Answer 30

warmth, erythema, and tenderness of the joint together with constitutional symptoms and fever nearly always unilateral

Question 31

osteomyelitis

Answer 31

fever and bony tenderness/a limp

Question 32

endocarditis due to s. aureus

Answer 32

usually acute course most present with high fever common in IV drug users

Question 33

what bacteria causes many catheter associated infections?

Answer 33

staph epidermidis

Question 34

what does staph saprophyticus cause

Answer 34

UTIs in sexually active young girls dysuria and pyuria responds to many antibiotics

Question 35

examples of s. aureus virulence factors

Answer 35

``` cell surface: 1. protein A 2. fibronectin binding protein 3. clumping factor 4. other MSCRAMMs secreted: 1. superantigen 2. cytolysins (toxins) 3. exoenzymes 4. polysaccharide intracellular adhesion ```

Question 36

function of capsule

Answer 36

inhibits phagocytosis

Question 37

function of protein A

Answer 37

binds to the H chain of Ab and can inhibit Ab opsonization, preventing phagocytosis can activate classical complement pathway with Ab/protein A complex

Question 38

how does s. aureus form a fibrin barrier around infectious loci?

Answer 38

coagulates plasma with coagulase | binds fibrinogen and causes production of fibrin

Question 39

how can s.aureus break down clots and why?

Answer 39

enzymes like staphylokinase break down fibrin and clots | breaks out of walled off areas to colonize rest of body

Question 40

function of toxins

Answer 40

toxic for many blood cells (aka cytotoxins, lysins)

Question 41

panton valentine leucocidin (PVL)

Answer 41

exotoxin occurs in <5% of strains phage derived causes leukocyte destruction and necrosis, especially in skin and lungs

Question 42

exfoliatin toxins

Answer 42

consist of ETA and ETB | result in scalded skin syndrome (SSSS)

Question 43

what is SSSS

Answer 43

fever, erythema, blisters blisters eventually rupture and leave a red base positive nikolskys sign (bullae moves under skin)

Question 44

bullous impetigo

Answer 44

localized SSSS culture positive (unlike disseminated SSSS) nikolskys sign not present primarily occurs in infants and young children

Question 45

which virulence factors are responsible for food poisoning with s. aureus

Answer 45

enterotoxins A-E and G-I superantigens that stimulate certain T cells stimulate production of cytokines such as IFN-y and TNF causing inflammation of the tissues

Question 46

symptoms of enterotoxins

Answer 46

often localized to gut, but can be fatal is systemic often occur from skin of food handlers cause vomiting and watery diarrhea 2-6 hours after ingestion usually self limited

Question 47

characterize toxic shock syndrome

Answer 47

caused by a superantigen first described in kids most frequently associated with tampons, but at least half of cases not associated with menstruation

Question 48

which exotoxins are associated with TSS

Answer 48

TSST-1 | enterotoxin B and C

Question 49

how to diagnose s. aureus

Answer 49

obtain cultures as appropriate for site of infection | blood cultures from patients with serious infections

Question 50

who is more susceptible to s. aureus infections?

Answer 50

neutropenic patients

Question 51

important factors in defense against s. aureus

Answer 51

1. neutrophils 2. opsonization w Ab and complement 3. T cells, Th17 recently implicated 4. IL-1 5. recognition by TLR-2

Question 52

what can defend against toxins?

Answer 52

antibody

Question 53

characterize coagulase negative staph

Answer 53

s. epidermidis most common lack many virulence factors cause problem in artificial heart valves