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]
Where are the bacteria contained in impetigo?
In the honey-colored exudate/crust
What is treatment for impetigo?
1. self-limited illness that resolves without treatment [if anything, just soap and water] 2. Topical treatment *Mupirocin - strep/staph *bacitracin - GABHS only *retapamulin - strep/staph/MRSA *penicillin- strep
How does erysipelas present? [RED]
What pathogen is causative?
It is an acute inflammation of skin with lymphatic involvement that presents with an
**advancing red, well-demarcated margin
Caused by M1 or M3 streptococci
What is facial erysipelas often mistaken for?
What prior event s it usually associated with?
How does it resolve?
Often mistaken for LUPUS.
Often, facial erysipelas is associated with a prior pharyngitis.
Resolves spontaneously
What is the typical cause of trunk erysipelas?
How does it resolve?
Surgical wound infection
It can be fatal!
What is effective antibiotic for erysipelas?
penicillin
A patient presents with a painful, tender, swollen erythematous leg following surgery, burn, wound, or minor trauma. The lesion is not well demarcated.
What infection is this most likely?
What layers of skin are involved?
What % will be bacteremic?
Cellulitis- dermis, subcutaneous tissue
10-20% will be bacteremic
What makes cellulitis different from erysipelas?
In cellulitis:
- lesions may NOT be raised
- margins are indistinct
What are 3 common predisposing factors for cellulitis?
- diabetes
- drug use
- bypass surgery
What are the most common pathogens to cause cellulitis?
Strep and Staph
A>B>C,G
What is lymphangitis?
What does it rapidly progress to?
What is it often accompanied by?
What happens if it is untreated?
Lymphangitis = spread of infection up lymphatics that presents as a linear red streak.
It is rapidly progressive to bacteremia in 24 to 48 hours
Accompanied by lymphadenitis [swollen, tender nodes].
Lethal if left untreated
An immunocompromised patient presents with erythema gangrenosum. What is the likely pathogen?
Pseudomonas aureginosa
A patient was swimming in a fresh water pond, and now has gastroenteritis and cellulitis. What is the likely cause and how is it treated?
Aeromonas hydrophila
-treat with 3rd generation cephalosporin
What 2 groups of people are most vulnerable for infection by vibrio vulnificus?
What is the reservoir for vibrio?
What is the gram staining of vibrio?
- Diabetics
- Cirrhotics
Reservoir = salt water/estuarine
Gram negative curved rod that is halophilic
A patient presents with a rapidly progressing cellulitis after a cat bite. What organism are you concerned about?
What is the gram staining capability?
What is treatment?
Pasteurella Multocida -gram negative coccobacilli
Treatment = augmentin because polymicrobial nature of animals mouth [need to cover anaerobes too]
What is necrotizing fasciitis?
Where on the body does it usually start? [RED]
It is gangrenous destruction of skin, fascia, and sometimes muscle.
It starts at a site of trauma [BUT THE SITE MAY BE INAPPARENT]
What are the prominent virulence factors in necrotizing fasciitis?
What are the 2 major things they do?
Bacterial toxins are the primary virulence factor
- strep
- clostridium
They:
- cause tissue separation and death of host cells
- death of neutrophils
What are the pathogens responsible for progressive bacterial synergistic gangrene?
When does this type of gangrene typically occur?
Strep, staph, coliforms, anaerobes
This usually occurs post-op
What are the pathogens responsible for synergistic necrotizing cellulitis?
What causes this?
Gram - enteric flora, anaerobes due to proximity to GU, GI
What is Fournier’s gangrene?
{RED}
scrotum and external genitalia necrotizing cellulitis
What pathogen gives:
- “flesh eating bacteria”
- gas gangrene/ myonecrosis
- GABHS -strep pyogenes
2. clostridium perfringens
A patient presents with rapidly progressing skin lesion.
The skin is indurated and “woody”. It started as red, but now it is dusky and purple. Bullae form and there is sloughing of the skin.
Pain is OUT OF PROPORTION TO FINDINGS [RED].
What is it likely that this patient has?
necrotizing fasciitis
How do you distinguish necrotizing fasciitis from cellulitis?
- systemic toxicity
- prostration
- rapidly spreading lesion
- bullae
How is diagnosis of necrotizing fasciitis made?
MICROBIOLOGICAL
- aspiration or tissue biopsy -get idea of underlying problem
- Gram stain for empiric treatment
- culture
RADIOLOGICAL- confirmatory
- plain film
- CT
- Shows gas in tissue
What is treatment for necrotizing fasciitis?
- Surgical debridement of infected tissue [RED]
- adjunctive antibiotics
- adjunctive HBO
- oxygen tension is directly toxic to Strep and Clostridium
- denatures some toxins
- increases neutrophil respiratory burst
What combo of drugs should be given as adjunctive treatment for the surgery if the pathogen is:
- clostridium
- streptococci
- coliforms
- anaerobes
- penicillin and clindamycin
- penicillin and clindamycin
- 3rd gen. cephalosporin, carbapenems, piperacillin/ticaricillin/clavulanate
- metronidazole, piperacillin/ticaricillin/clavulanate, carbapenems
What are the 2 major pathogens that cause myositis?
- Strep pyogenes - associated with TSS that grows in an infected wound, enters bloodstream, makes superantigen, and infects muscle
- Clostridium following blunt trauma or penetrating trauma
What are the 2 types of TSS?
Which is more fatal?
- S. aureus TSS from a tampon or wound–> TSST1 enters bloodstream [no bacteremia]–> fever, rash shock
- FATALITY = 3% - S. pyogenes TSS from wound –>BACTERIA enter bloodstream [bacteremia] produce superantigen [SpeA,C] and infect musle–>fever, rash, shock, myositis
- FATALITY =30%
What is the criteria for diagnosis of Streptococcal TSS?
- isolation of GABHS
- Hypotension [SBP<90] AND 2 of the following:
- renal impairment
- coagulopathy
- liver dysfunction
- ARDS
- Rash
- soft tissue necrosis
What is pyomyositis?
What is the causative agent? [RED]
What 3 people are you more likely to see it in?
What does it follow?
It is infection within the body of the muscle itself usually following blunt trauma
S. aureus
- diabetic
- IVDU
- HIV/immunocompromised
What are the 3 stages of pyomyositis?
- muscle swells, indurated, diffusely tender
- red, swollen, POINT tender, DISCRETE ABSCESS
- systemically ill, bacteremic, fever, hypotension, shock
How do you diagnose pyomyositis? {RED}
- IMAGING TO LOCATE ABSCESS [US, CT, MRI]
2. aspiration for micro diagnosis
What is treatment for pyomyositis?
Drain the abscess
Antibiotics for s. aureus [vanc, linezolid, dapto]
