Bacterial infections of the skin

BACTERIAL SKIN INFECTIONS

Dr. Hadaf Aljunaiyeh

OBJECTIVES

After completing this lecture, the student should be able to: Describe the morphology of common cutaneous bacterial infections. Discuss the bacterial etiologies of cellulitis and erysipelas. Become familiar with superinfection of resident normal flora Recommend initial steps for the evaluation and treatment of common cutaneous bacterial infections.

NATURAL DEFENSE OF SKIN

RESIDENT MICROFLORA

RESIDENT MICROFLORA

TRANSIENT BACTERIA
S. aureus does not normally reside on the skin, but may be present transiently, inoculated from colonized sites such as the nares(30%), axillae & vagina This colonization is usually transient except in 10-20% where it becomes persistent, these are called staph carriers & are a hazard to the society.

PRIMARY BACTERIAL INFECTIONS

Impetigo & ecthyma Folliculitis Furuncles & Carbuncles Erysipelas Cellulitis


SECONDARY BACTERIAL INFECTION
Infection of previously damaged or diseased skin, such as Dermatitis Herpes simplex Burn Scabies & pediculosis any child presenting with recurrent impetigo of the scalp we should look for underlying pediculosis capitis.

IMPETIGO

Acute, contagious bacterial infection of the skinOf 2 types:Bullous: caused by S. aureusNon-bullous: mainly by group A ℬ heamolytic streptococciPeak incidence aged 2-5 years, but can affect older children & adultsM=FCan be primary or secondary

NON- BULLOUS IMPETIGO

Caused by strept., staph., or usually a mixture of 2 A thin walled vesicle on erythematous base, soon ruptures & a crust forms (yellowish brown= honey colored) Heals without scarring Regional adenitis & fever in severe cases Can affect any part, except palms & soles Mostly exposed parts, especially central face

BULLOUS IMPETIGO

Mostly caused by s. aureus Mostly in newborn Target area is the face, but can occur anywhere even palm & soles Bullae are larger, persist longer(2-3 days), contents are first clear then become turbid, then rupture forming thin varnish-like brownish crusts

ECTHYMA

A lesion of neglect, develops at site of old traumaMostly elderly, diabetic, debilitated, or alcoholic patients (= vagabond’s disease)Caused by strpt. pyogenes, & staph.Mostly on lower limbsAdherent crust, beneath which is a purulent irregular ulcer, delayed healing with scarring.

COMPLICATIONS

lymphangitis, lymphadenitis. Staphylococcal scalded skin syndrome (SSSS). Post streptococcal acute glomerulonephritis, especially in cases due to streptococcus pyogenes M type 49


TREATMENT
Wet compresses with antiseptic solution to remove crusts with topical antibiotics is enough in mild cases. If severe or a nephritogenic strain of strept is suspected; then a systemic antibiotic is added as flucloxacillin , erythromycin or cephalexin.

STAPHYLOCOCCAL INFECTIONS: 1- SUPERFICIAL FOLLICULITIS:

Inflammatory disease of the hair follicles, which may be infectious or non infectious The infection is superficial involving the ostium of the hair follicle Usually caused by staph aureus Common on scalp of children, beard, axillae, extremities, buttocks Heal spontaneously in 1 week, or become chronic In adults can progress to boils

FOLLICULITIS

Can be: 1- infective: bacteria & yeast (pityrosporum) 2- Chemical: by mineral oils 3-physical: as after hair epilation

2- DEEP FOLLICULITIS(=FURUNCLES= BOILS)

Staphylococcal infection of the hair follicles, similar to but deeper than folliculitis Start as firm, red, tender papule that becomes painful &fluctuant nodule, finally ruptures & discharges pus, leaving a scar Sites of friction & sweating; mostly neck, buttocks & ano-genital area due to staph. carriage at these areas Constitutional symptoms may be present Some have recurrent attacks (=chronic furunculosis)

CHRONIC FURUNCULOSIS

They may recur at intervals for no apparent cause, these patients are staph carriers (they carry s. aureus in their nostrils, axillae & groins) They may be treated by topical antibiotics applied to carrier sites Long courses of oral flucloxacillin Care about hygiene & predisposing factors

CARBUNCLE

Collection of boils Swollen suppurating painful areas discharging pus from several points In areas of thick inelastic skin the infection spreads to subcutaneous fat such as nape of neck, back & thighs More painful & severe with constitutional symptoms More in diabetics Blood stream invasion may occur


MANAGEMENT OF FOLLICULITIS
Correction of underlying causes: diabetes, anemia, poor hygiene.Swabs for culture from lesions & carrier sites.Topical & systemic antibiotics.Incision of boils & carbuncle to speed healing.Recurrent boils need treatment of carrier states by b.d. topical antibiotics for 6 weeks+ improve patient’s hygiene.

STREPTOCOCCAL INFECTIONS: ERYSIPELAS & CELLULITIS

Cellulitis: infection of the subcutaneous tissue Erysipelas: infection of the dermis & upper part of subcutaneous tissue by group A ℬ heamolytic strept.

ERYSIPELAS

Minor cracks or wounds in the skin are the port of entry Starts with severe constitutional symptoms Followed by appearance of rapidly spreading painful erythematous plaque with well defined margins. May show hemorrhage or blistering 80% occur on the face Can be fatal if untreated

CELLULITIS

Similar to erysipelas, with some differences 1- deeper level of skin involvement (subcutaneous tissue) 2- Other organisms than strept. can cause it, like s. aureus 3- more raised & swollen but less well-defined border 4-More on the lower limbs than the face

CELLULITIS

COMPLICATIONS
1- recurrences may lead to lymphedema 2- subcutaneous abscess 3-Septicemia 4- nephritis

TREATMENT

Rest, analgesia Systemic antibiotics especially penincillin E.g: benzyl penicillin 600-1200 mg IV/6 hourly Or cephalosporin


ERYTHRASMA
Caused by corynebacterium minutissimum a member of resident floraAsymptomatic, well demarcated, scaly, reddish brown Body folds: axilla, groins, toe webs Coral red fluorescence with Wood’s lampTreated by topical antifungal, antibiotics, or sometimes systemic erythromycin

BACTERIAL

STAPH.
STREPT.
MIXED
SUPERFICIAL
FOLLICULITIS
ERYSIPELAS
IMPETIGO
DEEP
FURUNCLES & CARBUNCLES
CELLULITES