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BACTERIAL INFECTIONS OF THE SKIN
Introduction
• Infections with pyogenic (pus forming) bacteria• usually Staphylococcus aureus and/or Streptococci
(usually Group A β-haemolytic Streptococci - GABS)
Factors in development of bacterial skin infection
1) the portal of entry 2) the host defences 3) the pathogenic properties of the organism
Classification
- primary infections (pyodermas) - secondary infections
Primary infections (pyodermas)
• infections that are produced by the invasion of normal skin by a single species of pathogenic bacteria
Secondary infections
• Infections after the integrity of the skin has been broken, or the local immune milieu is altered by the primary skin condition
AD, scabies, tinea, …• may show mixture of organisms
Staphylococcus - Commonly carried in nose(35%), perineum (20%), axillae and toe webs (5-10%) - Staphylococcus causes impetigo,
folliculitis, and carbuncles plus deeper infections. - Staph. toxins (epidermolytic) cause
bullous impetigo and SSSS( Staphylococcal
scalded skin syndrome).
Streptococcus - Rarely found on normal skin, often in
throat (10%), occasionally in nose - Main pathogenic type – Lancefield
Group A. - Causes Erysipelas, cellulitis,
lymphangitis, regional lymphadenitis - Post streptococcal state (1-3 weeks
later) can produce – acute GN, rheumatic fever,
rheumatism, erythema nodosum,
psoriasis.
Normal Flora
• organisms that characteristically survive and multiply in various ecologic niches of the skin
• S. epidermidis is the principal staphylococcal species
• Candida • Malasazia furfur , propionibacterium acne
Superficial Cutaneous infections
Impetigo
• infections in the epidermis• untreated pyodermas can extend to the dermis, resulting in ecthyma
Two clinical patterns
• Bullous impetigo and • Non-bullous impetigo
Non-bullous Impetigo70% of impetigo industrialized countries -- S. aureus and
less often by group A streptococcus in developing countries – group A streptococcus remains a common cause
Occurs in children of all ages and adultsusually spreads from nose to normal skinpruritis or soreness
Cutaneous Lesions• initially a transient vesicle or pustule honey- colored crusted plaque
• surrounding erythema• 90% of prolonged, untreated –
regional LAP• may progress to Ecthyma
Bullous Impetigo• by phage group II S. aureus• Three types of eruptions 1) bullous impetigo, 2) exfoliative disease( SSSS) 3) staphylococcal scarlet fever• Extracellular exfoliative toxins
("exfoliatin") types A and B
Cutaneous lesions • more common in new-borns and
infants• rapid progression of vesicles to flaccid
bullae• bullae arises on normal skin• fluid clear yellow- dark yellow –
turbid- collapse – may crust
Laboratory
• Gram stain• Culture• Histology
Treatment - good hygiene removal of crusts. - Antibiotics - topical if mild - mupirocin, fusidic
acid, - Systemic if severe, multiple lesions, - cloxacillin, Erythromycin,
amoxi+ clavulanic acid, cephalexin
Ecthyma usually a consequence of neglected impetigocharacterized by thickly crusted erosions or
ulcerationsCaused by Group A Strept and/or Staph
Commonest in children or debilitated adults, homeless and soldiers
• most commonly on the lower extremities• ulcer has a “punched out” appearance• Covered with dirty greyish-yellow crust• heals slowly
• Treat as impetigo
Folliculitis
• a pyoderma that begins within the hair follicle
• a small, fragile, dome-shaped pustule occurs at the infundibulum (ostium or opening) of a hair follicle
• Children – scalp• Adults - beard area, axillae,
extremities, and buttocks• Can complicate to Furuncles if
untreated
Furuncles – boil • deep-seated inflammatory nodule that
develops around a hair follicle• areas with friction, occlusion, and perspiration• usually from a preceding, more superficial
folliculitis
Cutaneous Lesions
• solitary or multiple • hard, tender, red folliculocentric nodule• undergoes abscess formation Ruptures
Carbunclemore extensive, deeper, communicating, lesion
that develops when multiple, closely set furuncles coalesce.
more serious inflammationred and indurated, and multiple pustules soon
appear on the surface, draining externally around multiple hair follicles scar
fever and malaise - ill
• beware of bacteremia from such lesions esp when appears on the face
• infection such as osteomyelitis, acute endocarditis, or brain abscess
• recurrent furunculosis
Treatment• a systemic antibiotic as impetigo for mild cases• severe infections or infections in a dangerous
areas - maximal antibiotic dosage by the parenteral route
• drain if abscess
Erysipelascaused by group A β- haemolytic
streptococcusacute infection of skin- level of part of
dermissuperficial cellulitis with marked dermal
lymphatic vessel involvementface or a lower extremitysuperficial erythema, edema with a sharply
defined margin to normal tissue
• there may be portal of entry• Recurrent erysipelas – tinea pedis,
lymphedema surgery • Can cause lymphedema
Cellulitisinfection extends deeper into the dermis and
subcutaneous tissueS. aureus and GAS – common causeslooks erysipelas but lack of distinct margins,
deeper edema, surface bulla/necrosis can go deep if untreated – fasciitis regional LAPportal of entry evident in half of cases
Treatment • Supportive - rest, immobilization, elevation, moist heat,
analgesia.• Dressings -cool sterile saline dressings for removal of
purulent exudates and necrotic tissue• Surgical - Drain abscess
• Antimicrobial Therapy
- against Strept in erysipelas - against staph in cellulitis + /- against Strept
THANKS