Jackson: Skin and Soft Tissue Infections I Flashcards Preview

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Flashcards in Jackson: Skin and Soft Tissue Infections I Deck (60)
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1

Definitions:

Macule
Papule
Vesicle
Boils (Furuncle) and Carbuncles

Macule: flat, red inflammatory response to microbe or toxin

Papule: raised, red with more marked inflammation

Vesicle: blister

Boils (Furuncle) and Carbuncles: due to infection of hair follicle (folliculitis)

2

Definitions

Ulcer:
Impetigo:
Erysipelas:
Cellulitis:
Necrotizing Fascitis:

Ulcer: epithelium ruptures and microbe is discharged

Impetigo: bullous, crusted or pustular eruption

Erysipelas: well-defined spreading inflammation of dermal lymphatics

Cellulitis: acute inflammation due to infection of subcutaneous fat

Necrotizing Fascitis: inflammatory response in soft tissue below the site of infection

3

Dermatophytic fungi

Infection site:
Disease:

Keratinized epithelium

Ringworm

4

Impetigo

Infection site:
Microbe:

Epidermis

S.pyogenes and/or S.aureus

5

Erysipelas

Infection site:
Microbe:

Dermis
S.pyogenes

6

Folliculitis, boils (furuncles), carbuncles

Infection site:
Microbe:

Hair follicles
S.aureus

7

Cellulitis

Infection site:
Microbe:

Subcutaneous fat
S.pyogenes or S.aureus

8

Necrotizing faciitis

Infection site:
Microbe:

Fascia
Anaerobes

9

Gas gangrene

Infection site:
Microbe:

Muscle
Clostridium perfringens

10

Typhoid Fever

Pathogen:
Skin manifestation:

Salmonella typhi
Contaminated petechia

11

What does Neisseria meningitidis cause?

Skin manifestation:

Septicemia, meningitis
Contaminated petechia

12

What causes scarlet fever?

S. pyogenes

13

What causes TSS?

S.aureus

14

What causes Blastomycosis?
Skin manifestation:

Blastomyces dermatitidis

Granulomatous lesion

15

Staphylococcus Aureus

Virulence Factors (Relevant to Skin/Soft Tissue Infections) (6):

Alpha toxin
Toxic Shock Syndrome Toxin (TSST-1)
Exfoliative Toxins
Exoproteins for spread
Antiphagocytic components
Quorum sensing

16

Staphylococcus Aureus
Alpha toxin

o 7 subunit pore-forming cytolysin (complement-like MOA)
o Pore permits fluid loss from cell (kills erythrocytes, leukocytes)

17

Staphylococcus Aureus
Toxic Shock Syndrome Toxin (TSST-1):

Pyrogenic exotoxin (related to those produced by Group A strep)

Superantigen that cross-links T cell receptor and MHC class II, resulting in cytokine release

Cytokines cause diverse effects, including endotoxic shock

18

Staphylococcus Aureus
Exfoliative Toxins:
Two types:

Two types:

Chromosomal

Plasmid-encoded

19

What causes scalded skin syndrome?
What layers are split?

Staph Aureus exfoliative toxins cause scalded skin syndrome by inducing intercellular splitting between straum spinosum and stratum granulosum (desquamation of upper layers of epidermis)

20

Staphylococcus Aureus
Exoproteins for Spread (2):

Hyaluronidase (hydrolyzes connective tissue)

Staphylokinase (promotes fibrinolysis)

21

Staphylococcus Aureus
Antiphagocytic Components (3):

Protein A: binds Fc portion of IgG (Ab binds upside down)

Coagulase: promotes surface polymerization of fibrin to resist phagocytosis

Catalase: neutralizes hydrogen peroxide (protective mechanism since it is an aerobe)

22

Quorum sensing regulates:
Upregulates what at low density?
What at high density?

Quorum sensing regulates virulence factor expression in response to cell density
1. Upregulation of coagulase at low cell densities for colonization
2. Upregulation of staphylokinase at high densities for spread

23

Staphylococcus Aureus

Transmission:

o High skin and nasal carriage rates in humans
o No acquired immunity
o Transmission occurs by fomites (inanimate objects)

24

Staphylococcus Aureus

Pathogenesis:

Furuncle:
Carbuncle:
Scalded Skin Syndrome (Bullous Exfoliation):
Toxic Shock Syndrome:
Wound Contamination:

Furuncle:
Colonization of hair follicle (folliculitis)
Coagulation of fibrin around lesion

Carbuncle:
Focal suppuration (abscess)
May lead to entry of organism into bloodstream via lymphatics

Scalded Skin Syndrome (Bullous Exfoliation):
Common in neonates and children (often pick up from hospital workers)
Caused by exfoliative toxin
Bullous Impetigo


Toxic Shock Syndrome:
Caused by TSST-1
Results from vaginal colonizers (ie. tampons in too long) or wound infection

Wound Contamination:
Bacteremia and endocarditis

25

What is bateremia?
What can it lead to? (4)

Bacteremia: spread to blood stream via lymphatics; can result in
Endocarditis
Osteomyelitis
Meningitis
Pulmonary infection

26

What is Bullous Impetigo?

Localized scalded skin syndrome

27

Staphylococcus Aureus
Clinical Identification of Organism:

Collection
G+ or G-?
Catalase
Coagulase
Antimicrobial Susceptibility testing

Specimen Collection: surface swab, blood, pus (pyogenic) cultured on blood agar

Gram positive cocci in clusters

Catalase Positive:

Coagulase Positive:

Antimicrobial susceptibility testing allows you to determine the MIC of a particular antimicrobial against S.aureus

28

Staphylococcus Aureus
Antimicrobial Susceptibility Testing:
Allows you to determine:

o Allows you to determine the MIC (minimum inhibitory concentration) of a particular antimicrobial against S.aureus
o Once you determine MIC, can determine if that drug is a therapeutic option (ie. does MIC fall into proper dosing range)

29

Staphylococcus Aureus

Coagulase Positive:

Differentiates from:

Coagulation of citrated plasma by culture

Differentiates from other staphs (S.epidermis or S.saprphyticus, which are less virulent)

30

Staphylococcus Aureus

Catalase Positive:
Produces:
Differentiates from:

Produces O2 bubbles when hydrogen peroxide is added

Differentiates from strep (catalase negative)