The Structure of Human Skin

-       Perspiration and sebum contain nutrients

-       Salt inhibits microbes

-       Lysozyme hydrolyzes peptidoglycan

-       Fatty acids inhibit some pathogens

 

Mucous Membranes

-       Line body cavities

-       The epithelial cells are attached to an extracellular matrix

-       Cells secrete mucus

-       Often acidic

-       Some cells have cilia

-       In eyes, washed by tears with lysozyme

 

Normal Microbiota of the Skin

-       Gram-positive, salt-tolerant bacteria

-       Staphylococci

-       Micrococci

-       Diphtheroids

-       Grow on oils

-       Aerobes on surface

-       Corynebacterium xerosis

-       Anaerobes in hair follicles

-       Propionibacterium acnes

-       Yeast

-       Malassezia furfur

 

Microbial Diseases of the Skin

-       Exanthem: Skin rash arising from another focus of the infection

-       Enanthem: Mucous membrane rash arising from another focus of the infection

 

Staphylococcal Skin Infections

-       Staphylococcus epidermidis

-       Gram-positive cocci, coagulase-negative

-       Staphylococcus aureus

-       Gram-positive cocci, coagulase-positive

 

Staphylococcus aureus

-       Antibiotic resistant

-       Leukocidin

-       Resists opsonization

-       Survives in phagolysosome

-       Lysozyme resistant

-       Exfoliative toxin

-       Superantigen

 

Staphylococcal Skin Infections

-       Folliculitis: Infections of the hair follicles

-       Sty: Folliculitis of an eyelash

-       Furuncle: Abscess; pus surrounded by inflamed tissue

-       Carbuncle: Inflammation of tissue under the skin

-       Impetigo: crusting (nonbullous) sores, spread by autoinoculation

 

Scalded Skin Syndrome

-       Toxic shock syndrome (TSS)

-       Toxic shock syndrome toxin 1

-       Scalded skin syndrome

-       Bullous impetigo

-       Impetigo of the newborn

 

Streptococcal Skin Infections

-       Streptococcus pyogenes

-       Group A beta-hemolytic streptococci

-       Hemolysins - lyse red blood cells

-       Hyaluronidase - dissolves connective tissue component haluronic acid

-       Streptolysins - lyse red blood cells, toxic to neutrophils

-       M proteins - from cell wall, binds to neutrophils to activate them; helps bacterium attach and resist phagocytosis

 

Streptococcal Skin Infections

-       Meningitis

-       Pneumonia

-       Sore throat

-       Otitis media

-       Endocarditis

-       Puerpural fever

-       Dental caries

-       Necrotizing fasciitis

-       Erysipelas

 

Invasive Group A Streptococcal Infections

-       Exotoxin A, superantigen

 

Streptococcal Toxic Shock Syndrome

-       M proteins

-       Complex with fibrinogen

-       Binds to neutrophils

-       Activates neutrophils

-       Release of damaging enzymes

-       Shock and organ damage