Chapter 18 Flashcards
Where are normal skin flora number higher?
In moist areas
How does shedding protect from viral skin infections?
Viruses cannot replicate in dead cells
What are the routes of skin infections?
Break of intact skin (infection from outside)
Skin manifestations of systemic infections
Toxin mediated skin damage (toxin in blood to skin)
What is staphylococcus aureus?
The most common skin pathogen, “swiss army knife” has virulence factors to counter almost every defence mechanism we have
What do staphylococcal skin infections cause?
Boils, abscesses to scaled skin syndrome, Toxic shock syndrome
What is the resistant form of staph aureus?
Methicillin resistant staph aureus
What is a boil?
A superficial infection of the hair follicle (folliculitis)
How does a boil progress?
Infection of the hair follicle multiplies and locally spread to cause an inflammatory reaction and an influx of neutrophils (pus), may drain inward and spread the bacteria
How is a boil treated?
Daring, antibiotics for severe infections (with fever)
Who will have recurrent infections of staphylococcus skin infections?
Nasal carriers will have recurrent infection
What happens in scalded skin syndrome?
The exfoliation toxin destroys the intercellular connections of the skin causing separation of the epidermis and large blisters
How is scalded skin syndrome treated?
Fluid replacement and antibiotics
What is Toxic Shock Syndrome?
Systemic infections from staph aureus that affect multiple organ systems
What are the symptoms of TSS?
Fever, hypotension, diffused red rashes and desquamation of the skin (limited to palms and soles of feet)
Why do tampons cause TSS?
The synthetic absorbent material holds lots of blood, which is the growth media for staph aureus (vaginal microflora) and produces toxins
What is the cause behind many streptococcal skin infections?
S. pyogenes
Group A streptococci
What are some streptococcal skin infections?
Impetigo and erysipelas, cellulitis, necrotizing fasciitis
How does impetigo occur?
Strep is acquired through contact with infected skin lesions and then it invades minor breaks in the skin, causing lesions. Deeper=lesions
What is erysipelas?
An acute deeper infection of the dermis by strep. Can lead to bacteremia. Red rosy rash on face
What does the virulence of GAS depend on?
Climate, humidity, race, trauma
How is the s. pyogenes that infects the skin different from the one that infects the throat?
Subdivision of the species based on surface proteins (M proteins attached to PG)
What is the incubation time for S. pyogenes skin infections?
24-48 hours post skin invasion
What are the virulence factors of S. pyogenes?
Hyaluronidase and toxic products to facilitate its spread through the tissue
What is the lysogenized strain of S. pyogenes? What does it do?
A strain that has been lysogenized by macrophages and now produces pyrogenic endotoxin causing a red rash
What may S. pyogenes of the skin cause?
A toxic shock like syndrome
What is cellulitis?
A diffuse inflammation and infection of the skin, deeper than erysipelas and originates from a superficial infection or following trauma
May have systemic features
What are the systemic features that may occur with cellulitis?
Fever, malaise, headache, elevated white blood cell count
How is cellulitis treated?
Use empirical antibiotic treatment until cause is known (most likely Gram + cocci)
What causes cellulitis usually?
S. pyogenes, GAS
What is necrotizing fasciitis?
A ‘flesh-eating disease’
Acute, highly toxic infection with a high mortality rate resulting from trauma to the skin
What causes necrotizing fasciitis?
Often polymicrobial
Anaerobes, facultative anaerobes like S. pyogenes (don’t need oxygen)
How do facultative anaerobes cause blisters?
They produce gas
What causes gas gangrene?
Clostridial sp (C. perfringens) Anaerobes
How does C. perfringens work?
Contamination with spores Produces lecithinase (like snake venom) which precipitates protein
What are the clinical manifestations of gas gangrene?
Severe pain, edema, cellulitis, production of gas and foul-smelling purulent discharge
How is gas gangrene treated?
Amputation, hyperbaric chamber (saturates with O2 to kill anaerobes) and antibiotics
How can we tell if a pathogen is producing lecithinase?
Put sample on egg white media, put in antibodies against lecithinase which will bind and inactivate, stopping it’s precipitation of proteins.
