Microbiology 2 - Skin infections Flashcards
S. aureus infections. Describe the bacteria
Gram positive, commensal.
Has cell wall and membrane –> susceptible to treatment with penicillin
High skin infection rates occur in?
Hot humid countries
What are the medical considerations of S. aureus
MRSA
Toxins produced by S. aureus:
- Panton valentine leuocidin
- Exfoliative toxin - causes splitting of epidermis
- TSST-1
- Enterotoxin
Can also cause bone, joint, lung infections and sepsis
Describe the manifestations of s. aureus skin infections
Impetigo - infection of sub corneal layer of epidermis (i.e. v superficial)
Folliculitis - infection of mouth of hair follicle
Ecthyma - infection of full thickness of epidermis (and maybe some superficial dermis)
Boil - abscess of hair follicle (try and let pus out)
Carbuncle - abscess of several adjacent hair follicles
What is one of the classic features of a s. aureus infection?
Golden crust
Describe staphylococcal scalded skin syndrome
Exfoliative skin toxin enters blood - becomes systemic and causes cleavage of epidermis away from initial infection site
Describe treponema pallidum
Gram negative spirochaete
- cause of syphilis (STD)
- 12 million new cases per year worldwide - increases transmission of HIV
Describe the phases of syphilis
Primary (3-8 weeks) - painless ulcer at inoculation site (chancre)
Secondary (6-12 weeks) - disseminated infection, generalised rash and lymphadenopathy
Latent syphilis - no clinical signs
Tertiary syphilis (usually years later) - skin, neurological and vascular manifestations/lesions - can cause thoracic aneurysms
Congenital syphilis —> acquired perinatally if mother has latent syphilis –> crosses placenta
What is congenital syphilis associated with
Miscarriage Stillbirth Prematurity Rashes Brain and neurological problems Bone disease
How many herpes viruses are there?
8 (we only need to know 3 though)
HHV-1/2/3
NB - HHV3 = varicella zoster virus
All 3 target mucoepithelial cells
HHV1/2 cause oro-genital herpes
HHV 3 causes chickenpox and shingles
All 3 HHV latent in neurones
What are the 2 types of herpes and what are their clinical presentations
Type 1 - oral herpes
Type 2 - genital herpes
Clinical presentations - vesicular rash (2 weeks)
- eczema herpeticum
- herpes encephalitis
What do HSV1, HSV2 and VZV all have in common
They have latency
Initial infection subsides - virus lives on in body in dormant state –> e.g. neurones (DRG). Upon reactivation, occurs in same place as initial activation
How do you treat eczema herpeticum
Acyclovir
How is VZV (chickenpox) spread?
Inhalation or close contact
Face most dense area of vesicles
If VZV comes back after dormancy what do you get?
Herpes zoster –> comes when patient immunocompromised
aka shingles —> follows one dermatome usually one one side
IF it gets the back of the eye –> it can cause blindness
There are 2 types of superficial skin fungal infections
- Dermatophytes - e.g. trichophyton rubrum. Grow in keratin. Long hyphae, grow from tip
- Yeasts - e.g. candida. Grow on warm, wet surfaces. Single cell and bud
What is tinea unguium
Fungal infection of the nails - usually dermatophytes (but can be yeasts)
Treated by taking anti-fungals
What is tinea capitis
Fungal infection of the head, doesn’t affect adults
May be a kerion (looks like an abscess type lesion - it is a type of tinea capitis)
What other tineas are there
- Tinea magnum - hands
- Tinea pedis - feet
- Tinea cruris - affects schema of scrotum
- Tinea facei - face
What fungal skin infection may yeasts cause
Candida intertrigo
Wet, eczema like red rashes. May occur in mouth, genital area, under breast, etc
treated with topical antifungals
How are fungal infections of the hair and nails treatedd
With a systemic antifungal (can’t use topically as infection is too deep)
What is scabies (sarcoptes scabei) caused by
Mites
Transmitted from human to human via skin to skin contact
Mites burrowing in the surface of epidermis - just below stratum corneum
Commonly occurs in hands, wrists, toes, etc
No initial symptoms in first few weeks –> then get type 4 hypersensitivity to mite –> widespread itchy eczematous rash
Treat with insecticide
