Skin Infections Flashcards by Hayley Gilfillan

What type of staphylococci is a Commensal vs pathogenic

Coag negative e.g. Staph epidermis - Commensals
Coag positive e.g. Staph aureus - Pathogenic

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name 3 common skin commensals

Staph epidermis
Corynebacteria species (aka diptheroids)
Cutibacteria (propionibacterium species)

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Cellulitis vs erysipelas

Cellulitis - infection of lower dermis and subcutaneous tissue
Erysipelas - similar but affects upper dermis and lymphatics

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What type of cellulitis is a medical emergency

Periorbital cellulitis

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Where does cellulitis typically affect & what are the two main causative organisms

Lower limb
Strep. pyogenes, Staph. aureus

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Cellulitis clinical presentation

Red hot swollen, painful skin that is slightly shiny
+/- systemic symptom

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Cellulitis risk factors

•Previous cellulitis
•Broken skin (eczema, tinea, trauma)
•Lymphoedema
•High BMI
•CKD, chronic liver disease
•Immunosuppression

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Cellulitis diagnosis

Often clinical
Swab if pus present or broken skin

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Cellulitis management

Flucloxacillin (strep pyogens & staph aureus cover)

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What type of microorganism is strep pyogens

Group A beta haemolytic streptococci

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What infections can be caused by staphylococcus aureus

Wound, skin, bone & joint infections

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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

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Staph aureus drug of choice (MSSA)

flucloxacillin for MSSA

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Certain strains of staph aureus can produce toxins. Name two

SSST - staphylococcal scalded skin syndrome toxin
PVL - Panton valentine leucocidin

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Staph aureus drug of choice (MRSA)

Doxycycline O
Vancomycin IV

Not flucoxacilin
Other options - Cotrimoxazole, clindamycin

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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)

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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