Transcript wood varnish

Chapter 16
Bacterial infections
Resident flora of the skin
• The surface of the skin teems with micro-organisms, which are
most numerous in moist hairy areas, rich in sebaceous glands.
• Organisms are found, in clusters
• Mixture of harmless and poorly classified
– Staphylococci: Staphylococcus epidermidis, NOT aureus
– Micrococci
– Diphtheroids:
• Aerobic diphtheroids predominate on the surface
• Anaerobic diphtheroids (Propionibacteria sp.) deep in
the hair follicles.
– Several species of lipophilic yeasts also exist on the skin.
Erythrasma
• Some diphtheroid members of the skin flora produce
porphyrins.
• Symptom-free macular wrinkled
• Slightly scaly pink
• Brown or macerated white areas
• Found in the armpits, groins or between the toes.
• In diabetics, larger areas of the trunk may be involved.
• Diagnosis (Wood’s light  coral pink).
• DDx: tinea pedis
• Treatment:
– Topical fusidic acid
– Topical antifungal Miconazole
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Macular wrinkled
Slightly scaly pink
Wood’s light  coral pink
Staphylococcal infections
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S.aureus is not part of the resident flora
Carried in nostrils, perineum or armpits
Multiply on areas of diseased skin such as eczema
Cause:
– Impetigo
– Ecthyma
– Furunculosis (boils)
– Carbuncle
– Scalded skin syndrome
– Toxic shock syndrome
Impetigo
• Erosions in the stratum corneum
• Caused by
– Staphylococci (bullous type)
– Streptococci (crusted ulcerated)
– Both
• S. aureus produce Exfoliative toxins, which cleave the cell
adhesion molecule desmoglein, If the toxin
– Localized  blisters of bullous impetigo
– Generalized  widespread blistering as in the
staphylococcal scalded skin syndrome.
• A thin-walled flaccid clear blister
• May become pustular
• If rupture leave
• Extending area of exudation
• Yellowish varnish-like crusting.
• Multiple
• Particularly around the face.
• More obviously bullous in infants.
• A follicular type of impetigo
(superficial folliculitis) is also
common.
Fig. 16.2 Widespread impetigo due to
Staph. aureus with erosions and cruising.
Course:
• Spread rapidly through a family or class.
• Clear even without treatment.
Complications:
• Acute glomerulonephritis (Streptococcal impetigo).
DDx:
• Herpes simplex
• Eczema.
• Scalp lice (esp. in recurrent impetigo of head & neck)
Investigation:
• Clinically.
• Swab & culture
Treatmant: (after investigation)
• Systemic antibiotics (flucloxacillin, erythromycin or cefalexin)
• penicillin V (nephritogenic strain of streptococcus)
• Removal of crusts by compressing them & application of a topical
antibiotic (neomycin, fusidic acid, mupirocin or bacitracin)
Ecthyma
• Full thickness ulcer  Heals with scarring
• Ulcers forming under a crusted surface infection.
• The site may have been that of
– Insect bite
– Neglected minor trauma
Furunculosis (boils)
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Acute pustular infection of a hair follicle
Usually with Staphylococcus aureus
Adolescent boys are especially susceptible to them.
Tender, red nodule enlarges, may discharge pus
its central ‘core’ before healing to leave a scar
Fever and enlarged draining nodes are rare.
Most patients have 1-2 boils only, and then clear.
The sudden appearance of many furuncles suggests a virulent
staphylococcus including strains of community-aquired
MRSA.
• A few unfortunate persons experience a tiresome sequence of
boils (chronic furunculosis).
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Tender
Red
Nodule enlarges
May discharge pus
Enlarged swollen mass
with purulent material
Fig. 16.3 Chronic furunculosis.
Complications:
• Cavernous sinus thrombosis (boils in central face).
• Septicaemia
DDx:
• Hidradenitis suppurativa (groin and axillae).
Investigations in chronic furunculosis
• General examination: skin disease (scabies, pediculosis, eczema).
• Test the urine for sugar. Full blood count.
• Culture swabs from lesions and carrier sites.
• Immunological evaluation only
Treatment
• Acute episodes:
• incision & drainage.
• Systemic antibiotics (fever or immunosuppressed).
• Chronic furunculosis
• topical antiseptic or antibiotic (treat carrier sites twice daily for 6 weeks).
• Treat family carriers in the same way.
• Stubborn cases
• systemic antibiotic (for 6 weeks)
• Daily bath using an antiseptic soap.
• Improve hygiene and nutritional state, if faulty.
Carbuncle
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A group of adjacent hair follicles becomes deeply infected
Swollen painful suppurating area
Discharging pus from several points.
More severe than boil.
Diabetes must be excluded.
Treatment:
• Topical and systemic antibiotics.
• Incision and drainage (speed up healing)
• DDx: fungal kerion in unresponsive carbuncles.
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Swollen painful
Discharging pus
Scalded skin syndrome
Cause
• Exfoliative toxins by staphylococcal infection, that cleave the
superficial skin adhesion molecule desmoglein 1  acantholysis.
• Loosening of large areas of overlying epidermis, cause:
– Erythema
– Tenderness
• Affects children and patients with renal failure
• Most adults have antibodies to the toxin.
• Treatment: systemic antibiotics
• DDx: toxic epidermal necrolysis
• Investigation: ski biopsy (to exclude toxic epidermal necrolysis).
Fig. 16.4 Staphylococcal scalded skin syndrome in a child.
The overlying epidermis is loosening in the red areas.
Toxic shock syndrome
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Cause: staphylococcal toxin
Fever
Rash (widespread erythema)
Sometimes circulatory collapse
Most marked on
– Fingers and hands.
– Vagina of women using tampons
• Treatment:
– Systemic antibiotics
– Irrigation
Generalised erythema
Streptococcal infections
• Erysipelas
• Cellulitis
• Necrotizing fasciitis (surgical emergency)
Erysipelas
• Acute skin infection
• Split in the skin (perhaps a minor tinea pedis)
– Between the toes
– Under an ear lobe
• Start as malaise, shivering & fever.
• After a few hours  red plaques
• Well-defined
• Blisters may develop on the red plaques
Treatment:
• Untreated, the condition can even be fatal
• Systemic penicillin (sometimes given IV).
Recurrences:
• Can affect the same area repeatedly, so lead to persistent lymphoedema.
• Treated by low dosage long-term oral penicillin V.
Fig. 16.5 Erysipelas – note sharp spreading
edge, here demarcated with a ballpoint pen.
Cellulitis
• Inflammation of the skin.
• Cause (streptococci, staphylococci or other organisms)
• Occurs at a deeper level than erysipelas.
– The subcutaneous tissues are involved
– The area is more raised and swollen
– The erythema less marginated than in erysipelas.
• Cellulitis often follows an injury
• Favours areas of hypostatic oedema.
• Treatment
– Elevation
– Rest
– Systemic antibiotics (sometimes given IV)
Cellulitis
Spreading inflammation of subcutaneous or
connective tissue