BACTERIAL INFECTIONS BACTERIAL INFECTIONS OF THE SKINOF THE SKIN

IntroductionIntroduction

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 cellulitis, lymphangitis, regional lymphadenitis - Post streptococcal state (1-3 weeks later)

can produce – acute GN, rheumatic fever, rheumatism, erythema nodosum, psoriasis.

Normal FloraNormal Floraorganisms that characteristically

survive and multiply in various ecologic niches of the skin

S. epidermidis is the principal staphylococcal species

Candida Malasazia furfur ,

propionbacterium acne

Superficial Cutaneous Superficial Cutaneous infectionsinfectionsImpetigo

infections in the epidermisUntreated pyodermas can extend

to thedermis, resulting in ecthyma

Two clinical patterns

Bullous impetigo and Nonbullous impetigo

Non-Bullous Impetigo

70% 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

skin

Cutaneous Lesionsinitially a transient vesicle or

pustule honey-colored crusted plaque

Sunounding erythem90% of prolonged,untreated –

regional LAPMay progress to Ecthyma

Bullous Impetigoby phage group II S. aureuThree types of eruptions 1) bullous impetigo, 2) exfoliative disease( SSSS) 3) staphylococcal Scarlet feverExtracellular exfoliative toxins

("exfoliatin") types A and B

Cutaneous lesions more common in newborns and

infantsrapid progression of vesicles to

flaccid bullaebullae arises on normal skinfluid clear yellow- dark yellow –

tubid- collapse – may crust

Laboratory

Gram stainCultureHistology

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 – scalpAdults - beard area, axillae,

extremities, and buttocksCan 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

noduleundergoes 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

Treatmenta systemic antibiotic as impetigo

for mild casessevere infections or infections in

a dangerous areas - maximal antibiotic dosage by the parenteral route

drain if abscess

Erysipelascaused by group A β-hemolytic

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 entryRecurrent 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 – fesciitis regional LAPportal of entry evident if 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

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