Download BACTERIAL INFECTIONS OF THE SKIN

BACTERIAL INFECTIONS OF THE SKIN
The resident flora of the skin: Millions of micro-organisms are
present on the skin surface, mostly in hairy, moist areas rich in
sebaceous glands; it consists of a mixture of harmless & poorly classified
staphylococci, micrococci & diphtheroids.
Staphylococcus epidermidis, & aerobic diphtheroids predominate on the
surface, while anaerobic diphtheroids (propionibacterium) deep in the
hair follicles, for each person the skin flora remain stable & help to
defend the skin against outside pathogens by bacterial interference &
antibiotic production.
Staphylococcal infections:
Staphylococcus aureus is not part of the resident flora of the skin except
in a minority of people who carry it in their nostrils, axillae & groins.
Impetigo: a common acute superficial bacterial infection of the skin
caused by species of either staphylococci or streptococci or both, usually
the bullous type is by staphylococcus aureus, while the ulcerated crusted
type by β haemolytic streptococci.
Impetigo mostly occurs in young children especially in late summer,
sometimes complicating other skin diseases (secondary impetigo or
impetiginization) like scabies, pediculosis, eczema, burns & herpes
simplex, any child presenting with recurrent impetigo of the scalp we
should look for underlying pediculosis capitis.
Non-bullous impetigo: A disease of young children, beginning as
a thin walled vesicle which ruptures rapidly to form a golden crust on an
erythematous base, usually on the face (especially around nose &
mouth) & limbs, it starts as a single lesion but soon becomes multiple
due to autoinoculation, transmission is by direct skin to skin contact.
Bullous impetigo: the blisters in this type are caused by a
staphylococcal epidermolytic toxin, it's more common in neonates &
infants, & in older children due to insect bites, bullae (often quite large)
develop & last 2-3 days, initially clear, becoming cloudy then burst &
crusts develop, occur anywhere on skin especially the trunk.
Ecthyma: similar to impetigo, but characterized by ulceration under
a crusted surface & so heals with scarring, usually at the site of a minor
neglected trauma especially on the lower limbs in old people, it is
associated with poor hygiene & malnutrition.
Complications of impetigo: usually rare, like lymphangitis,
lymphadenitis, erysipelas & cellulites, & in streptococcal cases acute
glomerulonephritis.
Diagnosis: usually clinical, can be confirmed by swabs for Gram's stain
or culture.
Treatment: in mild cases topical treatment is enough with an antiseptic
solution to soften & remove the crusts, with a topical antibiotic as fusidic
acid, mupirocin or bacitracin , in severe cases or if a nephritogenic strain
of streptococci is suspected then a systemic antibiotic as flucloxacillin ,
erythromycin or cephalexin may be added.
Folliculitis, furuncles & carbuncles:
According to the level of affection of the hair follicle, folliculitis can be
divided into: superficial involving just the ostium of the hair follicle or
deep then called furuncles & carbuncles.
Superficial folliculitis: an extremely common condition, caused by
staphylococcus aureus, but can be traumatic as after hair depilation or
chemical as by mineral oils. The infective type is more common in
children presenting as pustules mostly on scalp or limbs & healing
spontaneously within 7-10 days, or they can become chronic, in adults
they can progress to boils.
Deep folliculitis(furuncles & carbuncles):
A furuncle(boil): is an acute, deep, pustular infection of the hair
follicle by staphylococcus aureus, mostly in adolescent boys, it starts as
a red, tender nodule, which enlarges to become pustular , fluctuant &
often tender, then ruptures discharging pus & their central core, leaving a
scar after healing, they can occur anywhere but mostly on the neck,
buttocks & anogenital area due to staphylococcal carriage in these sites.
There may be constitutional symptoms,
Patients may have single or recurrent attacks (chronic furunculosis).
A carbuncle: a collection of boils resulting from infection of adjacent hair
follicles, occurring usually in middle-aged men, mostly on the shoulders,
neck & hips. & conditions like diabetes or immuno-suppressive therapy.
Presenting as swollen painful, suppurating area discharging pus from
several points, it's exquisitely tender with severe constitutional
symptoms,
Management of recurrent boils:
1) Look for underlying causes if any, like diabetes, eczema, scabies..etc.
2) We can also send swabs for culture from lesions & carrier sites (nose,
& perineum).
3) Topical & systemic anti-staph antibiotics should be used, with possible
incision & drainage of boils & carbuncles to speed healing.
4) Chronic boils need treatment of carrier sites by topical antibiotic twice
daily for 6 weeks.
5) Attention should be paid to improve hygiene of the patient by frequent
bathing, with a good diet.
Streptococcal skin infection:
Erysipelas: acute infection of the skin caused by group A β haemolytic
streptococci, the infecting organisms enter the skin through minor cracks
or wounds & it starts with malaise, shivering & fever followed by
appearance of a rapidly spreading painful & tender red plaque with a
well-defined margins, the inflammation is in the dermis & subcutaneous
tissue, blisters may develop on the lesions. Most lesions occur on the
face (80%) of the cases, but the lower limbs or any other site may be
affected, fortunately it responds rapidly to systemic penicillin (sometimes
given intravenousely), the prognosis is bad, & can be fatal if left
untreated.
Recurrent attacks often occur affecting the same area each time with
eventual lymphoedema due to destruction & subsequent fibrosis of
lymphatics, low-dose long- term oral penicillin V will end these
recurrences.
Cellulites: similar to erysipelas, with some differences:
1) Inflammation is at a deeper level involving the whole subcutaneous
tissue.
2) In addition to β haemolytic strept., cellulites may also be caused by
staph.aureus, or other organisms.
3) The lesions are more raised & swollen & the margins less well-defined
than in erysipelas.
4) Lower limbs are the commonest sites affected whereas the face is
mostly affected in erysipelas.
Treatment is by rest, elevation, with systemic antibiotics.
Other common infections of the skin:
Erythrasma:
caused by overgrowth of diphtheroid members of the skin flora by a
bacterium called corynebacterium minutissimum, resulting in an
asymptomatic, macular, well-defined, reddish brown lesion with mild
scaling, usually affecting body flexures as axillae, toewebs & groins, it
gives coral red fluorescence with Wood's lamp, treatment is by topical
antifungal as miconazole, or antibiotics as fusidic acid, sometimes
systemic erythromycines may be required.
Erysipeloid:
Occurring in butchers, cooks & fishermen, usually by a prick from an
infected bone, the infecting organism is erysipelothrix incidiosa.
It is usually a mild condition appearing as a swollen purple area with a
clear-cut advancing edge, around the inoculation area. Usually resolves
spontaneously within few weeks or a quicker response may be achieved
with penicillin treatment.