Skin Infections Flashcards
What type of staphylococci is a Commensal vs pathogenic
Coag negative e.g. Staph epidermis - Commensals
Coag positive e.g. Staph aureus - Pathogenic
name 3 common skin commensals
Staph epidermis
Corynebacteria species (aka diptheroids)
Cutibacteria (propionibacterium species)
Cellulitis vs erysipelas
Cellulitis - infection of lower dermis and subcutaneous tissue
Erysipelas - similar but affects upper dermis and lymphatics
What type of cellulitis is a medical emergency
Periorbital cellulitis
Where does cellulitis typically affect & what are the two main causative organisms
Lower limb
Strep. pyogenes, Staph. aureus
Cellulitis clinical presentation
Red hot swollen, painful skin that is slightly shiny
+/- systemic symptom
Cellulitis risk factors
•Previous cellulitis
•Broken skin (eczema, tinea, trauma)
•Lymphoedema
•High BMI
•CKD, chronic liver disease
•Immunosuppression
Cellulitis diagnosis
Often clinical
Swab if pus present or broken skin
Cellulitis management
Flucloxacillin (strep pyogens & staph aureus cover)
What type of microorganism is strep pyogens
Group A beta haemolytic streptococci
What infections can be caused by staphylococcus aureus
Wound, skin, bone & joint infections
What distinguishes staph aureus from other staphylococci
Produces enzymes, including coagulase, an enzyme that clots plasma i.e. Staph aureus is a coagulase positive staphylococci
Staph aureus drug of choice (MSSA)
flucloxacillin for MSSA
Certain strains of staph aureus can produce toxins. Name two
SSST - staphylococcal scalded skin syndrome toxin
PVL - Panton valentine leucocidin
Staph aureus drug of choice (MRSA)
Doxycycline O
Vancomycin IV
- Not flucoxacilin
- Other options - Cotrimoxazole, clindamycin
What are the 2 main types of beta haemolytic streptococci & what do they cause
Group A beta haemolytic strep (throat, severe skin infections)
Group B beta haemolytic strep (meningitis in neonates)
Name a toxin released from beta haemolytic streptococci
haemolysin
What is necrotising fasciitis
Bacterial infection spreading along fascial planes below the skin surface causing rapid tissue destruction. It is a surgical emergency & requires debridement
What would make you think necrotising fasciitis
Severe pain that does not match what you see on the patients skin
+/- diffuse erythema, crepitus, purple skin discolouration
What bacteria is commonly associated with necrotising fasciitis
Group A (beta haemolytic) strep aka strep pyogenes
Patients with what infections should be isolated in a single room with contact precautions
Patients with…
- Group A strep infection
- MRSA infection
- Scabies
Should all leg ulcers be swabbed for infection
No - the underlying problem is vascular, only take swabs if there is signs of cellulitis or infection
What organisms on a leg ulcer swab would you want to treat
- Staph aureus
- Strep pyogenes (group A)
- Other beta haemolytic strep (group B, C, G)
- Anaerobes (esp in diabetics)
- Some gram negatives
Impetigo clinical presentation
Painful, itchy, highly contagious
Erythematous macule with vesicles/ pustules/ bullae
Superficial erosion with characteristic golden crust
Doesn’t just affect the face, but usually does
Impetigo likely causative organism
Staph. aureus &/ Strep. pyogenes
What is impetigo
Highly contagious superficial epidermal infection of the skin
Primarily caused by Staphylococcal and Streptococcal
Typically affects children & their face
Impetigo investigations
Usually clinical diagnosis
Bacterial swab for culture and sensitivity may be useful if:
- The impetigo is extensive or severe
- MRSA is suspected
- The impetigo is recurrent or resistant to treatment
Impetigo treatment
- 1st line: hydrogen peroxide 1% cream
- 2nd line: topical antibiotic cream e.g. fusidic acid
- If severe infection/ systemically unwell - O Flucloxacillin or Clarithromycin + topical fusidic acid
What is tinea & what is it commonly referred to as
Tinea is a superficial fungal infection of the skin caused by dermatophytes, a group of fungi that invade and grow in dead keratin; commonly referred to as ‘ringworm’
What microorganism cause tinea
Dermatophyte fungus
Different types of dermatophytes are associated with tinea infections in different body locations. Name some different tinea infections
- Tinea barbae (beard)
- Tinea capitis (head)
- Tinea corporis (body)
- Tinea cruris (groin)
- Tinea faciei (face)
- Tinea manuum (hand)
- Tinea pedis (foot) - ‘athlete’s foot’
- Tinea unguium (nail)
What is tinea pedis
Athlete’s foot
Tinea clinical features
Red, scaly patch
Often has an area of central clearing
This gives it a ring-like appearance
May be itchy
Tinea investigations
Scalp: Woods light (fluorescence) &
Body: Skin scrapings & culture
Tinea treatment
- 1st line => Topical antifungals e.g. clotrimazole and ketoconazole
- If scalp infection (tinea capitis) or onychomycosis => oral antifungal e.g. terbinafine or itraconazole
What is a side effect of oral anti fungals & what test must be carried out as a result of this
Oral anti-fungals can cause jaundice, cholestasis & hepatitis
LFTs should be checked before starting treatment and then every 4-6 weeks
How are dermatophyte infections transmitted
usually from other humans
but can also get it from animals & soil (very uncommon)
What is the most common dermatophyte
Trichophyton rubrum
Tinea pathophysiology
Dermatophyte enters abraded or soggy skin ->
Hyphae spread in stratum cornuem ->
Infects keratinised tissues only ->
Increased epidermal turnover causes scaling ->
Inflammatory response in dermis ->
Hair follicles & shafts invaded ->
Lesion grows outward & heals in centre ->
‘Ring’ appearance
Where does candida skin infections occur & why
Skin folds (where area is warm & moist)
E.g. breasts, groin, abdominal skin folds, baby nappy area
Candida diagnosis
Swab for culture
Candida treatment
clotrimazole cream, oral fluconazole
