MICROBIAL DISEASES OF THE SKIN AND
THE EYE
The skin
 Salt inhibits microbes
 Lysozyme hydrolyzes peptidoglycan
 Fatty acids inhibit some pathogens
NORMAL MICROBIOTA OF THE SKIN
 Gram(+) bacteria
 staphylococci and micrococci
 some these can survive at 7.5% NaCl
 diphtheroids
 Propionobacterium acnes
 Corynebacterium xerosis
 Yeasts
Pityrosporum ovale
 in oily skin and responsible for dandruff
SKIN lesions
 Macules
o flat, reddened lesions
 Papules
o raised lesions; with pus – pustules
 Plaques
o flat with elevated surface (plateau-like)
 Nodules
o rounded raised lesions more than 5 mm in dia
 Urticaria (wheals or hives)
o annular or ring like papules or plaques w/ pinkish color
 Vesicle
o small, fluid-filled lesions
 Bulla/Bullae
o vesicles larger than about 1 cm in diameter
 Pustules
o circumscribed, exudate-filled lesions
 Purpura
o skin lesion due to bleeding into the skin
 Petechiae-less than 3mm diameter
 Ecchymosis-more than 3mm diameter
 Ulcer
o crater-like that may involve the deeper layers of the skin
 Eschar
o necrotic ulcer covered w/ black scab or crust
RASHES
 Exanthem
-a skin rash that arises from disease conditions
 Enamthem
-a rash on mucous membranes
BACTERIAL DISEASES OF THE SKIN
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Staphylococcal Skin Infections
caused by staphylococci
cocci in clusters like grapes
Coagulase-positive
Staphylococcus aureus
Coagulase-negative
Staphylococcus epidermidis
1. Staphylococcus epidermidis
 90% normal microbiota of the skin
 generally pathogenic only when the skin barrier is broken or is invaded by medical
procedures
 able to form a slime layer of capsular material called biofilm.
2. Staphylococcus aureus
 most pathogenic
 Virulent Factors
 coagulase
coagulates blood to protect them from phagocytosis
 leukocidin - kills leukocytes
 exfoliative toxin - peeling-off of skin
 enterotoxin - food poisoning
Folliculitis
 hair follicles
 often occur as pimples
 IP: 4-10 days
 P/C: good hygiene
Sty
 infected follicle of an eyelash
Furuncle or Boil
 more serious hair folliculitis
 a type of abscess
Carbuncle
 hard, round deep inflammation of tissue under the skin
Impetigo of the Newborn
 thin-walled vesicles on the skin that rupture and later crust over
Scalded Skin Syndrome
 skin of the affected areas peels off in sheets
 exfoliative toxin
 toxemia
3. Streptococcal Skin Infections
 caused by streptococci
 cocci in chain
 Virulent Factors
 hemolysins - destroy RBCs
 alpha-hemolytic, beta-hemolytic, and gamma-hemolytic groups
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beta-hemolytic - complete hemolysis
most pathogenic
Beta-hemolytic streptococcus
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Subdivided further according to antigenic carbohydrates in their cell walls
GROUP A BETA-HEMOLYTIC
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subdivided according to the antigenic properties of the M Protein found in some strains
anti-phagocytic properties
for adherence and colonization of mucous membranes
GROUP A Beta-hemolytic streptococcus
Streptococcus pyogenes
 infects the dermal layer of the skin
 Erysipelas
 skin erupts into reddish patches with raised margins
 IP: usually 4-10 days
 P/C: good hygiene
 Virulent Factors
o Streptokinase
 dissolves blood clots
 Hyaluronidase
o Dissolves hyaluronic acid in connective tissues
 Deoxyribonucleases
o Degrades DNA
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Leukocidins
o Destroy leukocytes
Erythrogenic Toxins
o Responsible for red rash
 Scarlet fever
Exotoxin
o Superantigen
GROUP A Beta-hemolytic streptococcal infection
 Impetigo
 characterized by isolated pustules that become crusted and rupture
 Scarlet Fever
 Red rashes due to erythrogenic toxins
 IP: usually 1-3 days
 P/C: avoid contact
 Cellulitis
 Solid tissues
 Myositis
 Muscular tissues
 Necrotizing Fasciitis
INFECTIONS BY PSEUDOMONADS
Pseudomonas aeruginosa
 Aerobic Gram(-) bacilli
 Widespread in soil and water
 Can survive in any moist environment
 Can grow in soaps and cap liner adhesives
 Resistant to many antibiotics and disinfectants
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Toxins
Exotoxins
Endotoxins
Able to form biofilms
Produces blue-green pigment called pyocyanin
Can grow in flower vases, mop water, diluted disinfectants
Pseudomonas dermatitis
 Self-limiting rash of about 2 weeks’ duration
 Often associated with swimming pools, pool-type saunas, and hot tubs
 Otitis externa
Acne
3 Categories
1. Comedonal Acne
 Occurs when sebum channels are blocked with shed cells (whiteheads) and (blackheads)
2. Inflammatory Acne
 Propionibacterium acnes
 anaerobic
 Papules and pustules
 Isotretinoin
 Benzoyl peroxide
3. Nodular Cystic Acne
 Nodules or cysts
 Inflamed lesions filled with pus deep within the skin
 Isotretinoin
VIRAL DISEASES OF THE SKIN
1. warts
 Papillomas
 Papilloma virus
 Benign skin growth
 Treatment:
o Cold liquid nitrogen
o Topical drugs
o Burn with acids
2. Smallpox
 Variola
 Variola virus
 Variola major
 Variola minor
 Respiratory route
 Infect many internal organs
3. chickenpox
 Varicella
 Vesicular lesions fill with pus
 Face, throat, lower back, chest, shoulders
 Respiratory route
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Result of an initial infection with herpes varicella-zoster
4. Fever blisters
 Cold Sores
 Herpes Simplex Virus-1
 Painful, short-lived vesicles occur near the outer margin of the lips
 Respiratory route or oral route
5. measles
 Rubeola
 contagious
o Macular rash on the face and spreading to the trunk and
 Respiratory route
 Prevented by MMR
6. German measles
 Milder than rubeola
 Macular rash of small red spot with slight fever
 Respiratory route
 Prevented by MMR
FUNGAL DISEASES OF THE SKIN
Cutaneous mycoses
Dermatophytes
 Fungi colonize the hair, nails, and the outer layer of the epidermis
 Grow in the keratin present
 Dermatomycoses
 Tineas or ringworms
 Trichophyton – hair, skin, or nails
 Microsporum – hair or skin
 Epidermophyton – skin and nails
1. Tinea capitis
 Ringworm of the scalp
2. Tinea cruris
 Ringworm of the groin
 Jock Itch
3. Tinea pedis
 Ringworm of the feet
 Athlete’s foot
4. Tinea unguium
 Ringworm of the nails
 Onycho-mycosis
Subcutaneous mycoses
Sporotrichosis
 Sporothrix schenckii
extremities
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inhabit the soil, especially decaying vegetation
Small ulcerations on the hands
Candidiasis
 Candida albicans
 normal microbiota
 oral thrush or oral candidiasis
 overgrowth of the fungi
 Miconazole, nystatin
Parasitic infestation of the skin
1. scabies
 Sarcoptes scabiei
 tiny mite
 Burrowing under the skin to lay eggs
 Intense local itch
 Permethrin insecticide
 Ivermectin drug
2. pediculosis
 Pediculus humanus capitis
 Head louse
 Pediculus humanus corporis
 Body louse
 Permethrin insecticide
Microbial diseases of the eye
1. conjunctivitis
 Inflammation of the eye membrane
 Commonly called as pinkeye or redeye
 Hemophilus influenzae
 Adenoviruses
 Contact lenses
2. Neonatal gonorrheal Ophthalmia
 Neisseria gonorrheae
 Acquired as the infant passes through the birth canal
 Silver nitrate
 Antibiotics
 Diluted povidone iodine
3. Trachoma
 Chlamydia trachomatis
 Can also cause inclusion conjunctivitis in infants when passing the birth canal
 Corneal scarring and turned-in eyelashes
4. Herpetic keratitis
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Herpes Simplex Type 1 Virus
Infection of the cornea
Infectious blindness
5. Acanthamoeba keratitis
 Acanthamoeba species
 Fresh water, tap water, hot tubs, soil
 Contact lenses