Micro- Skin & Soft Tissue Infection Flashcards
What gram stain and hemolysis pattern is S. pyogenes?
Gram positive in pairs or chains that is GABHS
What 3 virulence factors allow S. pyogenes to adhere to host cells?
- M protein - binds to skin cells [RED ON SLIDES]
- Capsule- bind CD44
- ECM binding proteins -bind fibronectin, collagen, fibrinogen
What are the 4 virulence factors S. pyogenes uses to evade the immune system?
- M protein - anti complement
- Hyaluronate Capsule- anti-phagocytic [RED]
- Ig-binding proteins
- C5a peptidase - cleaves neutrophil chemotaxin
What 4 virulence factors are used by S. pyogenes to invade and spread in the host?
- Streptokinase - cleave fibrin thrombi to allow spread
- DNAse B - degrades DNA in pus
- SpeB - protease
- Streptolysins -lytic to cells
What are the 2 virulence factors S. pyogenes uses for toxicity?
- Superantigens -TSS
2. Pyrogenic Exotoxins [SpeA, SpeC]
What is the gram staining capability of Clostridium?
Spore forming or non-spore forming?
What is the oxygen requirements?
What are the 2 main habitats?
Gram positive rods
Spore forming
Anaerobic or microaerotolerant
Habitat = soil, intestines of animals [feces]
What is the most important type of clostridium for human disease?
What does t cause?
C. perfringens - Type A
It causes gas gangrene
Clostridium causes toxin-mediated syndromes in humans. There are at least 12 well-defined toxins. Which toxin is the most important?
What are the 2 most important virulence features of the toxin?
Alpha toxin
- phospholipase C - cleaves phosphatidyl choline
- hemolytic -WBC, RBC, platelets, endothelial cells
What 3 skin diseases are caused by C. perfringens?
- cellulitis
- necrotizing fasciitis
- Suppurative myositis and myonecrosis [RED on SLIDE]
In addition to skin diseases, what other disease is caused by C. perfringens?
How do you get it?
Gastroenteritis
-mild, self-limited diarrhea
You get this by eating meat that was stored too long at warm temperatures after cooking [spores survive initial cooking time are allowed to germinate]
What infections affect:
- epidermis and dermis
- border between dermis/subcutaneous fascia
- deep fascia
- muscle
- impetigo, erysipelas
- cellulitis
- necrotizing fasciitis
- myositis
What is the most important difference between uncomplicated and complicated skin infections? [RED on SLIDE]
Uncomplicated = monomicrobial [staph, strep, G+] Complicated = polymicrobial
What layers of skin are involved in uncomplicated infections?
What are the 3 diseases considered to be uncomplicated?
What are the usual pathogens?
What is required for therapy?
Uncomplicated affect:
Superficial layers of the skin with no underlying medical illness
-erysipela, impetigo, cellulitis
MONOMICROBIAL - G+ staph or strep
Therapy = antibiotics alone
What layers of the skin are involved in complicated infections?
What are the 3 diseases considered complicated?
What are the usual pathogens?
What is required for therapy?
Involves more than one layer of skin and is usually in IMMUNOCOMPROMISED or VASCULAR INSUFFICIENCY patient
- abscess, necrotizing fasciitis, ulcers
Polymicrobial pathogens
Therapy = surgical debridement AND antibiotics
The definition of a complicated skin infection is that is must have ONE or MORE of what 3 things?
- deeper soft tissue involvement [ulcer, fasciitis, abscess]
- significant surgical intervention
- underlying disease that complicates treatment
- vascular insufficiency
- immunocompromised
What pyoderma are usually caused by staph AND strep?
Which are usually staph only?
Staph or Strep = impetigo, ecthyma
Staph only = folliculitis, furuncle, carbuncle
What superficial infection presents with vesicles, honey-colored crust and NO scarring?
[RED on SLIDE]
Impetigo
What is ecthyma?
An infection that:
- penetrates through the epidermis
- MAY ulcerate
- MAY scar
Define furuncle and carbuncle.
Furuncle= small cutaneous abscess Carbuncle = furuncle that spreads into the dermis, coalesces and forms a draining sinus
What age group is most affected by impetigo?
What seasonal distribution?
What are the 2 most common pathogens? [RED]
How does transmission occur? [RED]
2-5 with poor hygiene
Summer [year round in tropical climates]
Staph and Strep [certain M types –49–are most common]
Transmission:
- direct contact - *person to person spread is common [RED]
- fomites
- insects
How long is incubation for impetigo?
What is the progression of symptoms?
Incubates 10-14 days
Papule–> vesicle–> pustule with erythema
Pustule ruptures in 4-6 days and leaves
*Honey-colored crust and exudate [RED]