Ch. 21 Microbial Diseases of the Skin and Eyes

Epidermis

thin outer potion of skin composed of layers of epithelial cells

Keratin

waterproofing protein coating outer layer of epidermis

Dermis

thick inner portion of skin, composed mainly of connective tissue

Mucous membranes

moist tissues that line the inside of the body, tightly packed epithelial cells attached to the basement membrane that secrete mucous

Normal skin microbiota

large numbers of gram positive cocci, gram positive pleomorphic rods

Cutibacterium/Propionibacterium

diptheroids that cause acne

Malassezia furfur

a type of yeast that causes dandruff

Vesicles

small, fluid filled lesions

Bullae

vesicles larger than 1 cm diameter

Macules

flat, reddened lesions

Papules

raised lesions

Pustules

raised lesions with pus

Exanthem

skin rash arising from a disease

Enanthem

rash on mucous membranes arising from a disease

Staphylococci skin infections

form irregular clusters, some produce coagulase

Coagulase

enzyme that clots fibrin in blood, used to identify types of Staphylococci

S. epidermidis

90% of normal ski microbiota, HAI, biofilm on catheters, coagulase negative

S. aureus

nasal passages of 20% of the population, golden-yellow colonies, coagulase positive, may produce damaging toxins

Folliculitis

infection of the hair follicles

Sty

follicultitis of an eyelash

Furuncle/boil

type of abscess, localized region of pus surrounded by inflamed tissue

Carbuncle

damage and inflammation of deep tissue from spreading furuncle

Impetigo

crusting sores, spread by autoinoculation

Scalded skin syndrome

bullous impetigo (fluid filled), toxin causes exfoliation

Toxic shock syndrome

fever, vomiting, shock, and organ failure caused by toxin 1 (TSST-1) in the bloodstream

how are Streptococci differentiated

based on antigenic cell wall carbohydrates, into groups A through T

Group A streptococci: S. pyogenes

produce various virulence factors: streptolysins, M protein, Hyaluronidase, strepto-kinases

streptolysins

lyse RBCs

M proteins

allow bacteria to adhere to mucous membranes

Hyaluronidase

dissolves connective tissue

Strepto-kinases

dissolve blood clots

Erysipelas

S. pyrogenes infects dermal layer of skin

Necrotizing fasciitis

S. pyrogenes relaxes pyrogenic toxins as a super-antigen, “flesh eating” disease

Streptococcal toxic shock syndrome

S. pyrogenes, similar to Staphylococcal TSS but more deadly

P. aeruginosa infections

gram negative, aerobic rod, produced exo and endotoxins, grows in biofilms, produces pyocyanin, causes hot tub folliculitis and otitis externa

pyocyanin

produced by P. aeruginosa, blue green outs in burn patients wounds

Eye diseases: conjunctivitis

inflammation of conjunctiva, pinkeye, commonly caused by Haemophiles infuenzae

Eye diseases: inclusion conjunctivitis

caused by Chlamydia trachomatis, transmitted to a newborn’s eyes

Eye diseases: trachoma

leading cause of blindness, caused by some serotypes of Chlamydia trachomatis, hand contact or flies

Eye diseases: Opthalmia neonatorum

Neisseria gonorrhoeae, ulceration of corneas, transmitted to newborn’s eyes

Viral skin diseases: warts

papillomas (benign tumor), contact and sexually, Papilloma virus

Viral skin diseases: Herpes simplex

HSV-1 (oral) and HSV-2 (sexual), 90% of US population has HSV-1, HSV-1 latent in trigeminal nerve ganglia, HSV-2 latent in sacral nerve ganglia near spine

Viral skin diseases: chickenpox/varicella

Herpesvirus varicella-zoster (HHV-3), respiratory transmission, Reye’s syndrome is severe complications with vomiting and brain dysfunction, latent in dorsal root ganglia

Viral skin diseases: shingles

Herpesvirus zoster, reactivation of latent varicella-zoster that moves from dorsal root ganglia along peripheral nerves to the skin

Viral skin diseases: smallpox/variola

Orthropoxvirus, variola major has 20-60% mortality, variola minor has <1% mortality, respiratory transmission, completely eradicated via vaccines

Viral skin diseases: monkeypox

related to smallpox, endemic to small animals in Africa, jumps from animals to humans

Viral skin diseases: measles/rubeola

respiratory transmission, cold like symptoms with macular rash, Koplik’s spots are red spots on the oral mucosa opposite the molars, prevented by the MMR vaccine

Viral skin diseases: german measles/rubella

Rubella virus (rubivirus), macular rash and light fever, respiratory transmission, congenital rubella syndrome causes fetal damage, deafness, heart defects, and mental retardation, prevented by MMR vaccine

Fungal skin and nail diseases: Cutaneous mycosis

colonize skin/hair/nails/outer epidermis, metabolize keratin, dermatomycosis is informally called ringworm or tineas, topical drug treatment

Fungal skin and nail diseases: Subcutaneous mycosis

more serious than cutaneous mycosis, penetrate cutaneous layer, caused by fungi inhabiting the soil, Candidiasis is overgrowth of Candida albicans (yeast) occurring in genitourinary tract and mouth, Thrush is Candida albicans infection of oral cavity

Arthropod skin diseases: Scabies

caused by mites (Sarcoptes scabiei), burrow in skin and lay eggs, sexual transmission, treatment with permethrin

Arthropod skin diseases: Lice/Pediculosis

Pediculus humanus captitis (head louse), Pediculus corporis (body louse), feed on blood, topical insecticides