• Skin is the first line of defense

• Normal microbiota help protect us

• Staphyloccocus and Streptococcus are common skin flora

• Skin lesions

• Vesicles = small, fluid-filled lesions
• Bullae = vesicles larger than about 1 cm in diameter
• Macules = flat, reddened lesions
• Papules (pustules) = raised lesions with pus

• Bacterial Infections of the Skin

• Two genera of bacteria, Staphylococcus and Streptococcus, are frequent causes of skin-related diseases
• Superficial staphylococcal and streptococcal skin infections are very common

• Staphylococci are divided up into coagulase-positive and coagulase-negative strains
• S. epidermidis may represent 90% of the normal microbiota
• Staphylococcus. aureus
• Gram positive cocci
• The most pathogenic of the staphylococci
• Produce a unique enzyme (coagulase)
  •  coagulates (clots) fibrin in blood

• The clot protects the organism from phagocytosis

• S. aureus
• Produce other enzymes and toxins
• A problem in hospitals
• Resistant to antibiotics
• Most commonly carried in the nose
• Enters skin though follicles
• Staphylococcal Skin Infections
• Folliculitis = infections of hair follicles (often occur as pimples)
• Sty = the infected follicle of an eye lash
• Furuncle (boil) = a type of abscess

• Folliculitis = infections of hair follicles (often occur as pimples)
• Sty = the infected follicle of an eye lash
• Furuncle (boil) = a type of abscess
• Folliculitis = infections of hair follicles (often occur as pimples)

• Sty = the infected follicle of an eye lash
• Furuncle (boil) = a type of abscess

• Abscess = a localized region of pus surrounded by inflamed tissue
• Carbuncle = boils that have grown together causing extensive damage

• Abscess = a localized region of pus surrounded by inflamed tissue
• Carbuncle = boils that have grown together causing extensive damage
• Carbuncle with contiguous Staphylococcus aureus infected sites
• Forms golden-yellow colonies
• Produce a distinctive smell
• Forms lots of pus

• Impetigo of the Newborn
• Primarily caused by staphylococci
• Symptoms
• Thin-walled vesicles of the skin
• Rupture and later crust over
• Hexachlorophene-containing skin lotions are commonly prescribed
• Impetigo - Staphyloccus aureus

• Scalded Skin Syndrome
• Due to a toxin produced by staphylococci
• Frequent in children under two, especially newborns
• A complication of staph infections
• Scalded Skin Syndrome
• Is first apparent as a lesion around the nose and mouth
• Develops into a bright red area and spreads
• Within 48 hours, the skin of affected areas peels off in sheets when it is touched
• Scalded Skin Syndrome
• The toxin breaks down the bond between the dermis and epidermis
• Lasts for a couple of days
• Patients are seriously ill and require vigorous antibiotic therapy
• Scalded Skin Syndrome
• Is also characteristic of the late stages of toxic shock syndrome
• A potentially life-threatening condition
• Characterized by fever, vomiting, a sunburn-like rash, and shock

• Streptococcal Skin Infections
• Streptococcal Skin Infections
• Streptococci are gram-positive spherical bacteria
• Usually grow in chains
• Streptococci cause a wide range of diseases
• Meningitis
• Pneumonia
• Streptococcal Skin Infections
• Sore throats
• Otitis media
• Endocarditis
• Puerperal fever
• Dental caries
• Streptococci secrete toxins and enzymes, including hemolysins, toxins that lyse RBCs
• Streptococcal Skin Infections
• Depending on the hemolysin they produce, strep are categorized as
• Alpha-hemolytic
• Beta-hemolytic
• Gamma-hemolytic (non-hemolytic)
• Streptococcal Skin Infections
• Beta-hemolytic strep are often associated with human disease
• This group is further differentiated into serological groups, A through T, according to antigenic carbohydrates in their cell walls
• Streptococcal Skin Infections
• Streptococcus pyogenes (= group A beta-hemolytic streptoccocci)
• Gram-positive cocci
• When it infects the dermal layer of skin, it causes erysipelas
• Erysipelas
• The skin erupts into reddish patches with raised margins
• Can progress to local tissue destruction
• If it enters the bloodstream, can cause sepsis
• Treated with penicillin
• Streptococcus Impetigo
• Most common in toddlers and children of grade-school age
• Characterized by isolated pustules that become crusted and rupture
• Spread mostly by contact
• Streptococcus Impetigo
• The bacteria penetrate the skin through some minor abrasion or insect bite
• Staphylococci are often found with this type of  impetigo
• Invasive Group A Infections
• More serious
• Strep that has reached deeper tissue
• Symptoms are due to enzymes and toxins
• Streptokinases
• Hyaluronidase
• Deoxyribonucleases
• Leukocidins
• Erythrogenic toxis
• Invasive Group A Infections
• Cellulitis- when strep attack solid tissue
• Myositis- when strep attack muscle
• Necrotizing fasciitis- when strep attack the muscle covering

• Infections by Pseudomonds
• Infections by Pseudomonads
• Pseudomonads
• Aerobic, gram-negative rods that are widespread in soil and water
• Can survive in any moist environment
• Can grow on traces of organic matter- soap films, cap-liner adhesives
• Infections by Pseudomonads
• Pseudomonads
• Are resistant to many antibiotics and disinfectants
• Pseudomonas aeruginosa
• An opportunistic pathogen
• Produces several exotoxins
• Infections by Pseudomonads
• Pseudomonads
• Cause outbreaks of Pseudomonas dermatitis
• Cause otitis externa (swimmer’s ear)
• Pseudomonas Dermatitis
• A self-limiting rash that lasts about two weeks
• Often associated with swimming pools, saunas, and hot tubes
• Hot water causes hair follicles to open wider, facilitating entry of bacteria
• Otitis Externa
• A painful infection of the the external ear canal leading to the eardrum
• Frequently caused by pseudomonads
• Infections by Pseudomonads
• P. aeruginosa
• A cause of nosocomial infections of indwelling medical tubes or devices
• A serious opportunistic pathogen in burn patients and patients with cystic fibrosis
• Grows easily in flower vases, mop water, etc.

• Acne
• Acne
• Probably the most common skin disease in humans
• Classified into three categories
• Comedonal acne
• Inflammatory acne
• Nodular cystic acne
• These require different treatments
• Acne
• Develops when sebum channels are blocked
• Comedos = whiteheads
• Comedones =  blackhead
• Sebum production is the root cause of acne
• Not related to diet
• Dependent on hormones
• Acne
• Comedonal acne is usually treated by topical agents
• Azelaic acid
• Salicyclic acid preparations
• Retinoids
• These topical agents do not affect sebum formation
• Acne
• Inflammatory acne
• Arises from bacterial action, especially Propionibacterium acnes
• P. acnes is an anaerobic diphtheroid commonly found on skin
• Acne
• P. acnes uses glycerol in sebum
• In metabolizing the sebum, it forms free fatty acids that cause an inflammatory response
• Inflammation leads to the appearance of  pustules and papules
• Acne
• Treatment for inflammatory acne
• Isotretinoin (Accutane) is used to reduce sebum production
• The drug is a teratogen
• Antibiotics targeting P. acnes can also be used
• Benzoyl peroxide = a drying agent
• Acne
• Treatment for inflammatory acne
• A new approach is the Clear Light system
• Affected skin is exposed to blue light that destroys P. acnes
• Acne
• Nodular cystic acne
• Characterized by nodules or cysts
• Leaves prominent scars on the face and upper body
• Treated with isotretinoin
• Must be used with extreme caution

• Viral Infections of the Skin
• Viral Infections of the Skin
• Warts
• Viral Infections of the Skin
• Warts
• Caused by the papillomavirus
• More than 50 types of papillomaviruses are known to cause different kinds of warts
• There is usually an incubation period of several weeks
• Viral Infections of the Skin
• Smallpox (Variola)
• Viral Infections of the Skin
• Smallpox (Variola)
• During the middle ages affected 80% of the population
• Those that recovered retained disfiguring scars
• Devastated Native American populations
• Viral Infections of the Skin
• Smallpox (Variola)
• Caused by an orthopoxvirus (the smallpox or variola virus)
• Two basic forms
• Variola major- mortality rate is 20% or higher
• Variola minor- mortlaity rate is less than 1%
• Viral Infections of the Skin
• Smallpox (Variola)
• Transmitted by the respiratory route
• Infects internal organs
• Then moves into the bloodstream
• Leads to infection of the skin and recognizable symptoms
• Viral Infections of the Skin
• Smallpox (Variola)
• Eradicated
• We have an effective vaccine
• There is no animal reservoir
• Monkeypox
• Resembles smallpox
• An orthopoxvirus
• Viral Infections of the Skin
• Monkeypox
• 100+ cases in Central Africa
• Is known to jump from animals to humans
• Transmission from human to human is limited
• Vaccination for smallpox is protective
• Viral Infections of the Skin
• Monkeypox was reported among several people in the U.S. in June 2003
• Most of these people became ill after having contact with pet prairie dogs that were sick with the virus.
• This was the first outbreak of monkeypox in the United States
• Viral Infections of the Skin
• Chickenpox (Varicella)
• Viral Infections of the Skin
• Chickenpox (Varicella)
• Caused by the varicella-zoster herpesvirus
• Herpes family viruses are notorious for going latent
• Viral Infections of the Skin
• Chickenpox (Varicella)
• The third most common reportable infectious disease in the U.S.
• Is more serious in adults
• A live, attenuated vaccine was licensed in 1995
• Viral Infections of the Skin
• Chickenpox (Varicella)
• Acquired by entry of the virus into the respiratory system
• The infection localizes in skin cells after about two weeks
• The infected skin is vesicular for 3-4 days
• Viral Infections of the Skin
• Chickenpox (Varicella)
• Vesicles fill with pus, rupture, and form a scab before healing
• Lesions are confined to the face, throat, and lower back
• Can also occur on chest and shoulders
• Viral Infections of the Skin
• Chickenpox (Varicella)
• If infection occurs during early pregnancy. It can damage the fetus in 2% of the cases
• Viral Infections of the Skin
• Reye’s syndrome
• A complication of viral infection (chickenpox, influenza, etc.)
• The use of aspirin to lower fever increases the chances of acquiring Reye’s syndrome
• Viral Infections of the Skin
• Reye’s syndrome
• A few days after the viral infection has receded, the patient
• Vomits
• Shows signs of brain dysfunction
• Coma and death can follow
• Affects children and teens especially
• Viral Infections of the Skin
• Shingles
• Viral Infections of the Skin
• Shingles
• Varicella-zoster virus can remain latent in the body
• After a primary infection, the virus enters the peripheral nerves
• Moves to a central nerve ganglion
• Viral Infections of the Skin
• Shingles
• Antibodies can’t penetrate into the nerve cell
• No viral antigens are expressed on the surface of the nerve cell- cytotoxic T cells are not activated
• The latent virus remains protected
• Viral Infections of the Skin
• Shingles
• Latent varicella-zoster virus is is located in the dorsal root ganglion near the spine
• Can be reactivated
• The trigger can be stress or lower immune competence due to aging
• Viral Infections of the Skin
• Shingles
• The virions move along the peripheral nerves to cutaneous sensory nerves of the skin
• Cause a new outbreak of the virus in the form of shingles (herpes zoster)
• Viral Infections of the Skin
• Shingles
• Vesicles occur but are localized in areas
• Typically are distributed about the waist (cingulum – girdle or belt)
• Can also occur on the face and on the upper chest and back
• Viral Infections of the Skin
• Shingles
• Sometimes the nerve infections can result in nerve damage that impairs vision or even causes paralysis
• Severe burning or stinging is a frequent symptom (postherpetic neuralgia)
• Viral Infections of the Skin
• Shingles
• Shingles of the optic nerve can cause blindness
• Shingles of the auditory nerve can cause deafness
• Viral Infections of the Skin
• Shingles
• Exposing children to shingles can lead to their contracting chickenpox
• Viral Infections of the Skin
• Herpes Simplex
• Viral Infections of the Skin
• Herpes simplex
• The herpes simplex viruses (HSV) can be separated into two groups
• HSV-1
• HSV-2
• HSV-1 causes cold sores (fever blisters)
• HSV-2 causes genital warts
• Viral Infections of the Skin
• Herpes simplex
• Cold sores (fever blisters) are painful, short-lived vesicles that occur near the outer margin of the lips
• Cold sores ? canker sores (sores on movable mucous membranes)
• Viral Infections of the Skin
• Herpes simplex
• HSV-1 usually remains latent in the trigeminal nerve ganglia
• Recurrences can be triggered by excessive exposure to UV radiation, emotional upsets, or hormonal changes associated with menstruation
• Viral Infections of the Skin
• Herpes simplex
• HSV-1 can be transmitted by skin contact among wrestlers and health professionals
• Herpes gladiatorum
• Herpetic whitlow- infections on the finger
• Viral Infections of the Skin
• Herpes simplex
• HSV-2 is transmitted primarily by sexual contact
• The usual cause of genital herpes
• Is latent in the sacral nerve ganglia near the base of the spine
• Viral Infections of the Skin
• Herpes simplex
• Very rarely, either type of herpes simplex virus may spread to the brain and cause herpes encephalitis
• Causes neurological damage
• Acyclovir can cure herpes encephalitis if administered promptly
• Viral Infections of the Skin
• Measles (Rubeola)
• Viral Infections of the Skin
• Measles (Rubeola)
• An extremely contagious viral disease
• Spread by the respiratory route
• Humans are the only reservoirs for measles
• The measles vaccine has almost eliminated the disease in the U.S.
• Viral Infections of the Skin
• Measles (Rubeola)
• Is especially hazardous to infants- have more serious serious complications
• Infection begins in the upper respiratory system
• Viral Infections of the Skin
• Measles (Rubeola)
• After an incubation period of 10-12 days, symptoms develop resembling those of the common cold
• Then a macular rash appears, beginning on the face and spreading to the trunk and extremities
• Viral Infections of the Skin
• Measles (Rubeola)
• The presence of Koplik’s spots is a diagnostic indicator of the disease
• Measles is extremely dangerous, especially in very young and very old people
• Viral Infections of the Skin
• Measles (Rubeola)
• Is frequently complicated by middle ear infections or pneumonia
• Encephalitis strikes 1 in 1000 measles victims, leading to permanent brain damage
• Viral Infections of the Skin
• Measles (Rubeola)
• A rare complication of measles- subacute sclerosing panencephalitis
• Occurs mostly in males
• Appears 1-10 years after recovery form measles
• Leads to death within a few years
• Viral Infections of the Skin
• Rubella (German Measles)
• Viral Infections of the Skin
• Rubella (German Measles)
• First described by German physicians in the 18th century
• A much milder viral disease than rubeola
• Often goes undetected
• Symptoms – macular rash of small red spots and a light fever
• Viral Infections of the Skin
• Rubella (German Measles)
• Complications are rare
• Encephalitis occurs in about 1 case in 6000, mostly in adults
• Transmission is by the respiratory route
• Incubation time = 2-3 weeks
• Viral Infections of the Skin
• Congenital rubella syndrome
• If a pregnant women contracts the disease during the first trimester, there is a 35% incidence of serious fetal damage- deafness, eye cataracts, heart defects, mental retardation, and death
• Viral Infections of the Skin
• Other Viral Rashes
• Viral Infections of the Skin
• Fifth Disease
• Viral Infections of the Skin
• Fifth Disease (Erytherma infectiosum)
• The fifth disease on a 1905 list of skin rash diseases
• Produces no symptoms at all in about 20% of those infected by the virus (human parvovirus B19)
• Viral Infections of the Skin
• Fifth Disease (Erytherma infectiosum)
• Symptoms are similar to a mild case of influenza
• There is a distinctive “slapped-cheek” facial rash that slowly fades away
• Viral Infections of the Skin
• Fifth Disease (Erytherma infectiosum)
• In adults, may cause anemia, an episode of arthritis, or, rarely, miscarriage
• Viral Infections of the Skin
• Roseola
• Viral Infections of the Skin
• Roseola
• A common, mild childhood disease
• Symptoms
• High fever for a few days
• Rash over much of the body for a day or two following the fever
• Caused by human herpesvirus 6

• Fungal Diseases of the Skin and Nails
• Cutaneous Mycoses
• Fungal Diseases of the Skin and Nails
• Mycosis = a fungal infection of the body
• Cutaneous Mycoses
• Dermatophytes = fungi that colonize the hair, nails, and the outer layers of the epidermis
• Grow on keratin
• These fungal infections are called dermatomycoses
• Fungal Diseases of the Skin and Nails
• Cutaneous Mycoses
• These fungal infections are called dermatomycoses (tineas or ringworm)
• Fungal Diseases of the Skin and Nails
• Examples of dermatomycoses
• Tinea capitis- ringworm of the scalp
• Tinea cruris- jock itch
• Tinea pedis- athlete’s foot
• Tinea unguium- infected nails
• Fungal Diseases of the Skin and Nails
• Subcutaneous Mycoses
• Fungal Diseases of the Skin and Nails
• Subcutaneous mycoses
• More serious than cutaneous mycoses
• Usually caused by fungi that inhabit the the soil, especially decaying vegetation
• Penetrate the skin through a small wound
• Fungal Diseases of the Skin and Nails
• Subcutaneous mycoses
• The most common subcutaneous disease in the U.S. is sporotrichosis
• Caused by the dimorphic fungus Sporothrix schenckii
• Fungal Diseases of the Skin and Nails
• Subcutaneous mycoses
• Most cases occur among gardeners and others working with soil
• The disease forms a small ulcer on the hands
• Seldom fatal
• Fungal Diseases of the Skin and Nails
• Candidiasis
• Fungal Diseases of the Skin and Nails
• Candidiasis
• Caused by Candida albicans
• C. albicans is usually suppressed by the bacterial microbiota of the mucous membranes in the genitourinary tract
• Fungal Diseases of the Skin and Nails
• Candidiasis
• The fungus is not affected by antibacterial drugs
• It overgrows mucosal tissue when antibiotics suppress the normal bacterial microbiota
• Changes in pH have similar effects
• Fungal Diseases of the Skin and Nails
• Vaginitis- is commonly caused by C. albicans
• Immunosuppresed individuals, are usually prone to Candida infections of the skin and mucous membranes
• Fungal Diseases of the Skin and Nails
• Immunosuppresed individuals, are usually prone to Candida infections of the skin and mucous membranes
• Fungal Diseases of the Skin and Nails
• Oral candidiasis (thrush)
• Affects newborn infants whose normal microbiota have not become established
• A whitish overgrowth of the oral cavity
• Oral Candidiasis

• Parasitic Infections of the Skin
• Scabies
• Parasitic Infections of the Skin
• Scabies
• Caused by a tiny mite (Sarcoptes scabiei)
• Burrows under the skin to lay its eggs
• Involves intense local itching
• The mite is transmitted by intimate contact
• Parasitic Infections of the Skin
• Scabies
• Can appear as a variety of skin lesions
• Can acquire secondary infections from scratching
• Treated with a solution of permethrin insecticide or gamma benzene hexachloride applied topically
• Parasitic Infections of the Skin

• Pediculosis (Lice)
• Parasitic Infections of the Skin
• Pediculosis (Lice)
• Infestations of lice
• Outbreaks of head lice among schoolchildren in the U.S. are common
• Lice require blood from the host and feed several times per day
• Parasitic Infections of the Skin
• Pediculosis (Lice)
• Itching leads to scratching and secondary infection
• During a life span of a little over a month, the female louse can produce several eggs (nits) per day
• Parasitic Infections of the Skin
• Pediculosis (Lice)
• Treatment include Nix (permethrin insecticide) and Rid (pyrethrin insecticide)
• Malathione can also be used
• combing with a fine tooth comb also helps

• Microbial Diseases of the Eye
• Conjunctivitis
• Microbial Diseases of the Eye
• Conjunctivitis
• An inflammation of the conjunctiva
• Also called redeye or pinkeye
• caused by the bacterium Haemophilus influenzae
• Viral conjuctivitis is caused by adenoviruses
• Microbial Diseases of the Eye
• Conjunctivitis
• The wearing of contact lenses has increased the incidence of infections of the eye
• Microbial Diseases of the Eye
• Bacterial Diseases of the Eye
• Bacterial Diseases of the Eye
• Neonatal Gonorrheal Ophthalmia
• A serious form of conjunctivitis caused by Neisseria gonorrhoeae
• Acquired by infant as he/she passes through the birth canal
• Carries a high risk of blindness
• Bacterial Diseases of the Eye
• Inclusion Conjunctivitis
• Caused by Chlamydia trachomatis
• An obligate intracellular parasite
• In infants, who acquire it in the birth canal, the condition tends to resolve itself in a few weeks or months
• Bacterial Diseases of the Eye
• Inclusion Conjunctivitis
• In rare cases, it can lead to scarring of the cornea
• Tetracylcine applied as an ophthalmic ointment is an effective treatment
• Bacterial Diseases of the Eye
• Trachoma
• A serious infection of C. trachomatis
• The greatest single infectious cause of blindness in the world
• In arid parts of Africa and Asia, almost all children are infected early in their lives
• Bacterial Diseases of the Eye
• Trachoma
• Also occurs occasionally in the southwestern U.S., especially among Native Americans
• The disease is transmitted largely by hand contact or by sharing towels
• Bacterial Diseases of the Eye
• Trachoma
• Flies may also carry the bacteria
• Eventually leads to permanent scaring
• Blindness can result from long-term mechanical abrasion of the cornea by scars and by turned-in eyelashes