Chapter 21

Microbial Diseases of the Skin and Eyes

Structure and Function of the Skin

• Skin = epidermis (keratin) + dermis– First line of defense (physical and chemical barrier)– Unbroken epidermis is an effective physical barrier– hair follicles, sweat gland ducts, and oil gland ducts

provide passageways for microbes to enter the skin and penetrate deeper tissues

– Perspiration provides moisture and some nutrients for microbial growth; sebum provides some nutrients

Skin• Perspiration contains

salt and antimicrobial peptide to inhibit microbes

• Lysozyme hydrolyzes peptidoglycan

• Fatty acids (from sebum) inhibit some pathogen

Figure 21.1

• Line body cavities

• Epithelial cells attached to an extracellular matrix (basement membrane)

• Cells secrete mucus

• Some have cilia

• Often acidic; limit microbial population

• Lysozyme in tears destroys the cell wall

Mucous Membranes

• Resistant to drying & tolerant to high salt

• Gram-positive, salt-tolerant bacteria– Staphylococci– Micrococci– Diphtheroids

• Vigorous washing can reduce numbers, but will not eliminate them

Normal Microbiota of the Skin

Figure 14.1a

Microbial Diseases of the Skin

Figure 21.2

• Exanthem– Skin rash arising from another focus of infection

• Enanthem– Mucous membrane rash arising from another focus

of infection

• Bacterial Disease of the Skin– Staphylococcus & Streptococcus are frequent

causes of skin-related diseases

Microbial Diseases of the Skin

• Staphylococci: gram-positive cocci in clusters

• S. epidermidis– Gram-positive cocci, coagulase-negative– very common on the skin (90% of the normal

microbiota); opportunistic pathogen

• Staphylococcus aureus– Gram-positive cocci, pathogenic S. aureus are

coagulase-positive– Leukocidin (destroy phagocytic leukocytes)– Exfoliative toxin (cause scalded skin syndrome)

Staphylococcal Skin Infections

Staphylococcal Skin Infections

– Enterotoxin (cause Staphylococcal food poisoning)

• S. aureus in hospital environment quickly becomes resistant to antibiotics (MRSA) and vancomycin-resistant S. aureus– Many S. aureus produce penicillinase

• Folliculitis– Infections of hair follicles

• Sty– Folliculitis of an eyelash

Staphylococcal Skin Infections

• Furuncle– Abscess; pus surrounded by

inflamed tissue

• Carbuncle– Inflammation of tissue

under the skin

• Impetigo of the newborn

• Toxemia

• Scalded skin syndrome

• Toxic shock syndrome (TSS)Figure 21.4

Streptococcal Skin Infections

• Gram-positive cocci in chains

• Secrete toxins and enzymes– Hemolysins (toxin): lyse red blood cells

• Alpha-, beta-, gamma-hemolytic streptococci

• Beta-hemolytic streptococci often associated with human disease– Further subdivided into different serological groups

(A through T)– Group A beta-hemolytic streptococci most

important

• Streptococcus pyogenes = group A beta-hemolytic streptococci

• M proteins– Antiphagocytic– Aid adherence

for colonization of mucous membrane

Streptococcal Skin Infections

Figure 21.5

Streptococcal Skin Infections

• Generally localized

• Can be highly destructive; produce substances that promote the rapid spread of infection– Streptokinases (dissolve blood clots)– Hyaluronidase (dissolves hyaluronic acid that

cement connective tissue)– Deoxyribonucleases (degrade DNA)– Erythrogenic toxins (cause red rash & other

symptoms of scarlet fever)

• Infects dermal layer of the skin

• Erysipelas– Can progress to local

tissue destruction

• Impetigo– Isolated pustules that

become crusted– Toddlers and

children of grade-school age

Streptococcal Skin Infections

Figure 21.6, 7

Invasive Group A Streptococcal Infections (“Flesh-eating bacteria”)

• Destroy tissue rapidly; mortality rates over 40%

• Streptokinases

• Hyaluronidase

• Exotoxin A (superantigen)

• Cellulitis

• Myositis

• Necrotizing fasciitisFigure 21.8

• Pseudomonas aeruginosa– Gram-negative, aerobic rod– Opportunistic pathogen; cause of many nosocomial

infections– Can grow on traces of unusual organic matter, soap

films or cap liner adhesives; often grow in dense biofilms

– Resistant to many antibiotics and disinfectants– Produce several exotoxins; also has endotoxin

Infections by Pseudomonads

Infections by Pseudomonads

• Pseudomonas dermatitis (swimming pool, hot tubs)

• Otitis externa (swimmer’s ear)

• Opportunistic pathogen – Cystic fibrosis patients – Post-burn infections pyocyanin produces

a blue-green pus in burn patients

• Most common skin disease• Caused by blockage of channels for the passage of

sebum to the skin surface • Three categories: comedonal acne, inflammatory

acne, & nodular cystic acne • Comedonal acne

– Occurs when sebum channels are blocked with shed cells

– Usually treated with topical agents that do not affect sebum formation

• Inflammatory acne– Due to Propionibacterium acnes (Gram-positive,

anaerobic rod)

Acne

Acne– Bacteria has a nutritional requirement for glycerol

in sebum inflammation caused by free fatty acids formed from metabolizing the sebum formation of pustules and papules

– Treatment:• Preventing sebum formation (isotretinoin teratogenic)• Antibiotics

– Benzoyl peroxide to loosen clogged follicles– Clear light system visible (blue) light (kills P. acnes)

• Nodular cystic acne– Formation of nodules or cysts = inflamed lesions

filled with pus deep within the skin leave prominent scars

– Treatment: isotretinoin

Viral Diseases of the Skin: Warts

• Benign skin growths caused by viruses

• Papillomaviruses different kinds of warts– Do not form cancer; but papillomaviruses are

associated with some skin & cervical cancer

• Transmitted through direct contact

• Treatment:– Cryotherapy: apply extremely cold liquid

nitrogen

Warts

– Electrodesiccation: dry them with an electrical current

– Burn them with acids– Topical application of prescription drugs

• Imiquimod (stimulate interferon production)

• Interferon (injection)

• Lasers (risk of aerosol transmission)

Smallpox (Variola)

• Smallpox virus (Orthopox virus)– Variola major has 20% mortality rate– Variola minor has <1% mortality rate

• Transmission by respiratory route

• Eradicated due to successful vaccination & there are no animal host reservoirs for the disease

• Bioterrorism vaccination only for military and healthcare workers

Smallpox (Variola)

• Monkeypox outbreak (started in zoo monkeys)

– Known to jump from animals to humans; human-to-human transmission is very limited• Seen some cases the USA recently

– Disease closely resembles smallpox in symptoms and mortality rate

– Prevention by smallpox vaccination

Chickenpox (Varicella) and shingles (Herpes Zoster)

• Chickenpox relatively mild in children; tends to be more serious in adults

• Results of initial infection with herpesvirus varicella-zoster (human herpesvirus 3)

• Transmitted via respiratory route & infection localized in skin cells

• Ability to remain latent within body cause shingles (a new outbreak of virus)

Chickenpox

Figure 21.10a

• Causes pus-filled vesicles

• Virus may remain latent in dorsal root

ganglia near the spine following a primary infection– persists as viral DNA– Escapes immune response

(Ab cannot penetrate into the nerve cells & no surface viral Ags expressed)

• Reactivation of latent HHV-3 releases viruses that move along peripheral nerves to skin.– Triggered by stress, or

lower immune competence due to aging

– Occur in distinctive areas (typically around waist); usually limited to one side of the body at a time

Shingles

Figure 21.10b

• HSV-1 (Human herpes virus 1, HHV-1) and HSV-2 (HHV-2)

• HHV-1 transmitted by oral or respiratory routes– Usually infected in infancy (subclinical infection)

• Cold sores or fever blisters (vesicles near the outer red margin of the lips)

• Remain latent in the trigeminal nerve ganglia– Recurrence due to excessive exposure to UV

radiation, emotional upsets, or hormonal changes

Herpes simplex virus (HSV)

Herpes simplex

• Herpes gladiatorum (vesicles on skin) via skin contact among wrestlers

• Herpes whitlow (vesicles on fingers) among healthcare workers

• HHV-2 transmitted sexually (genital herpes)

• Can remain latent in sacral nerve ganglia

• Herpes encephalitis, rare, but can be caused by both viruses HHV-2 has up to a 70% fatality rate

• Acyclovir may lessen symptoms

• Measles virus; humans are the only reservoir

• Transmitted by respiratory route; extremely contagious– Infectious before symptoms appear

• Macular rash and Koplik's spots (lesions of oral cavity; diagnostic indicator)

• Prevented by vaccination

• Complications of measles:– Encephalitis in 1 in 1000 cases– Subacute sclerosing panencephalitis in 1/1,000,000

Measles (Rubeola)

Measles (Rubeola)

Figure 21.13

• Rubella virus

• Transmitted via respiratory route

• Macular rash and fever

• Milder viral disease than rubeola (measles)

• Complications are rare (encephalitic in about 1/6,000, mainly in adults)

• Congenital rubella syndrome causes severe fetal damage during first trimester

• Prevented by vaccination

Rubella (German Measles)

Other viral rashes

• Fifth disease– A 1905 list of skin rashes included #1-measles,

#2-scarlet fever, #3-rubella, #4-Filatow-Dukes (mild scarlet fever), and #5-Fifth Disease

– Human parvovirus B19 produces mild flu-like symptoms with facial rash (“slapped-cheek”)

• Roseola– Human herpesvirus 6 causes a high fever and

rash, lasting for 1-2 days– Mild childhood disease

Fungal Diseases of the Skin and Nails

• Mycoses: any fungal infection of the body

• Cutaneous mycoses: fungal infection of the epidermis, nails, or hair

• Dermatophytes: fungi that colonize the hair, nails, and the outer layer of the epidermis– Metabolize keratin– Trichophyton: infects hair, skin, nails– Epidermophyton: infects skin and nails– Microsporum: infects hair and skin

• Dermatomycoses (tineas or ringworm)– Tinea capitis: ringworm of the scalp bald

patches– Tinea curis: ringworm of the groin, or jock itch– Tinea pedis: ringworm of the feet, or athlete’s foot– Tinea unguium (onychomycosis): nail infection

• Treatment– Oral griseofulvin (for hair infection)– Topical miconazole

Cutaneous mycoses

• Subcutaneous mycoses: fungal infection of tissue beneath the skin– Usually caused by fungi that inhabit the soil

• Sporotrichosis– Sporothrix schenckii enters puncture wound

form small ulcers on the hands– Occurs among gardeners or others who work

with soil– Treated with ingestion of a dilute solution of

potassium iodide (KI)

Subcutaneous mycoses

• Candida albicans (yeast)

• Candidiasis may result from suppression of competing bacteria by antibiotics

• Occurs in skin; mucous membranes of genitourinary tract and mouth

• Thrush is an infection of mucous membranes of mouth

• If infection becomes systemic fulminating disease leading to death

• Topical treatment with miconazole or nystatin

Candidiasis

Candidiasis

Figure 21.17

• Tiny mite Sarcoptes scabiei burrows in the skin to lay eggs

Parasitic infections of the Skin: Scabies

Figure 21.18

Scabies

• Intense local itching

• May appear as a variety of inflammatory skin lesions (due to secondary infections from scratching)

• Transmitted via intimate contact (sexually, too)

• Treatment with topical insecticides

Pediculosis (lice)

• Pediculosis: infestations by lice– Pediculus humanus capitis (head louse)– P. h. corporis (body louse) can spread

diseases (epidemic typhus)– Feed on blood– Itching due to sensitization to louse saliva– Scratching can lead to secondary infections– Lay eggs (nits) on hair

– Head louse has especially adapted legs to grasp scalp hairs

– Treatment with topical insecticides

– Combing out the nits with fine-toothed louse combs

Pediculosis (lice)

Figure 21.19

• Conjunctivitis (pinkeye): inflammation of the conjunctiva– Haemophilus influenzae & adenoviruses– Various microbes (bacteria, viruses, and protozoa)– Associated with unsanitary contact lenses

• Neonatal gonorrheal ophthalmia– Neisseria gonorrhoeae– Transmitted to newborn's eyes during passage

through the birth canal

Microbial Diseases of the Eye

Bacterial Diseases of the Eye

– Prevented by treatment newborn's eyes with antibiotics (silver nitrate in old days)

• Chlamydia trachomatis– Inclusion conjunctivitis

• Transmitted to newborn's eyes during passage through the birth canal

• Spread through swimming pool water

• Treated with tetracycline ointment

– Trachoma• Greatest cause of blindness worldwide

• Infection causes permanent scarring; scars abrade the cornea leading to blindness

• Transmitted by hand contact or by sharing personal objects (e.g. towels)

• Treated with tetracycline ointments; control through sanitary practices and health education

Bacterial Diseases of the Eye

• Keratitis: inflammation of the cornea

• Herpetic Keratitis– Herpes simplex virus 1 (HHV-1)– Infects cornea, may cause blindness– Treated with trifluridine

• Acanthamoeba keratitis– Transmitted from water– Associated with unsanitary contact lenses– Severe damage may require a corneal transplant

Other Infectious Diseases of the Eye

Microbial Diseases of the Eye

Figure 21.21

Chapter Review

1. Review the structure and function of skin as the first line of defense

• Skin = epidermis (keratin) + dermis– Unbroken epidermis is an effective physical barrier– hair follicles, sweat gland ducts, and oil gland ducts

provide passageways for microbes to enter the skin and penetrate deeper tissues

– Perspiration provides moisture and some nutrients for microbial growth; sebum provides some nutrients

Chapter Review– Perspiration contains salt and antimicrobial peptide

to inhibit microbes– Lysozyme hydrolyzes peptidoglycan– Fatty acids (from sebum) inhibit some pathogen

• Mucous membranes– Line body cavities– Epithelial cells attached to an extracellular matrix

(basement membrane)– Cells secrete mucus– Some have cilia

Chapter Review

– Often acidic; limit microbial population – Lysozyme in tears destroys the cell wall

• Normal microbiota of the skin– Resistant to drying & tolerant to high salt– Gram-positive, salt-tolerant bacteria (e.g.

Staphylococci, Micrococci, Diphtheroids)– Vigorous washing can reduce numbers, but will

not eliminate them recolonize the skin

Chapter Review2. Know the characteristics of bacterial

pathogens that cause skin diseases & the infections they cause

• Staphylococcus & Streptococcus are frequent causes skin-related diseases

• Pseudomonads are opportunistic pathogens• Staphylococcal skin infections

– Staphylococci: Gram-positive cocci in clusters– Staphylococcus epidermidis (S. epidermidis) are

coagulase-negative; 90% of the normal microbiota of the skin; opportunistic pathogen

Chapter Review

– Pathogenic S. aureus are coagulase-positive• Produce leukocidin (destroy phagocytic leukocytes);

exfoliative toxin (cause scalded skin syndrome); & enterotoxin (cause Staphylococcal food poisoning)

• Become antibiotic resistant quickly in hospital environment

– Diseases caused by S. aureus • Folliculitis: infections of hair follicles• Sty: folliculitis of an eyelash• Carbuncle : inflammation of the tissue under the skin• Impetigo of the newborn• Toxemia

Chapter Review• Scalded skin syndrome• Toxic shock syndrome

• Streptococcal skin infections– Streptococcus: gram-positive cocci in chains;

classified into three groups based on their hemolytic ability

• Alpha-hemolytic: partial hemolysis of red blood cells (RBCs)

• Beta-hemolytic: complete hemolysis of RBCs• Gamma-hemolytic: no hemolysis of RBCs

– Beta-hemolytic streptococci often associated with human disease; Group A most important

Chapter Review– Group A beta-hemolytic streptococci =

Streptococcus pyogenes (S. pyogenes)– S. pyogenes’ pathogenicity due to

• M proteins (adherence & antiphagocytic)• Streptokinases: dissolve blood clots• Hyaluronidase: dissolve hyaluronic acid• Deoxyribonucleases: degrade DNA• Erythrogenic toxins: cause red rash & other symptoms

of scarlet fever

– Diseases caused by S. pyogenes• Erysipelas• Impetigo

Chapter Review

• Invasive Group A Streptococcal infections– Especially pathogenic; “flesh-eating bacteria”– Destroy tissue rapidly; mortality rates over 40%– Produce streptokinases, hyaluronidase, exotoxin

A (major contributing factor by causing immune system to cause damage to the infected host)

– Diseases caused by invasive group A strep.• Cellulitis

• Myositis

• Necrotizing fasciitis

Chapter Review3. Know the viruses that cause skin diseases & the

infections they cause• Warts

– Papillomaviruses do not form cancer, but are associated with some skin & cervical cancer

• Chickenpox and Shingles– Results from initial infection with herpresvirus

varicella-zoster (human herpesvirus 3)– Ability to remain latent in body, when reactivated later

in life (a new outbreak of virus) cause shingles

Chapter Review

– Reactivation is triggered by stress, or lower immune competence due to aging

• Herpes simplex virus (HSV)– HSV-1 (human herpes virus-1, HHV-1) cause

cold sores or fever blisters (usually infected in infancy); herpes gladiatorum among wrestlers; herpes whitlow among healthcare workers

• Remain latent and reactivated due to excessive exposure to UV radiation, emotional upsets, or hormonal changes

Chapter Review

– HSV-2 (HHV-2) cause genital herpes• Can remain latent

– Both HHV-1 and HHV-2 can cause herpes encephalitic (rare) HHV-2 infection more fatal (70% fatality rate)

• Measles– Measles virus (Rubeola) extremely

contagious (infectious before symptoms appear)– Prevented by vaccination

Chapter Review

• German measles (Rubella)– Rubella virus; milder viral disease than measles– Prevented by vaccination

4. Know some fungal diseases of the skin and nails

• Cutaneous mycoses: fungal infection of the epidermis, nails, or hair– Caused by dermatophytes (fungi that colonize the

hair, nails, and the outer layer of the epidermis); metabolize keratin

Chapter Review• Trichophyton: infects hair, skin, nails• Epidermophyton: infects skin and nails• Microsporum: infects hair and skin

– Dermatomycoses (tineas or ringworm)• Tinea capitis: ringworm of the scalp bald patches• Tinea curis: ringworm of the groin, or jock itch• Tinea pedis: ringworm of the feet, or athlete’s foot• Tinea unguium (onychomycosis): nail infection

• Subcutaneous mycoses: fungal infection of tissue beneath the skin– Usually caused by fungi that inhabit the soil

Chapter Review• Sporotrichosis

– Sporothrix schenckii enters puncture wound form small ulcers on the hands

– Occurs among gardeners or others who work with soil

• Candidiasis– Candida albicans (yeast)– Candidiasis may result from suppression of competing

bacteria by antibiotics– Occurs in skin; mucous membranes of genitourinary tract

and mouth

Chapter Review

– Thrush is an infection of mucous membranes of mouth

– If infection becomes systemic fulminating disease leading to death

5. Know the infectious diseases of the eye and the pathogens that cause them

• Conjunctivitis (pinkeye): inflammation of the conjunctiva– Caused by various microbes (bacteria, viruses,

and protozoa)• Haemophilus influenzae & adenoviruses most

common cause

Chapter Review

• Inclusion conjunctivitis– Caused by Chlamydia trachomatis– Transmitted to newborn’s eyes during passage

through the birth canal– Spread through swimming pool water

• Trachoma– Also caused by Chlamydia trachomatis– Greatest cause of blindness worldwide; cause

permanent scarring; scars abrade the cornea leading to blindness

Chapter Review

• Keratitis: inflammation of the cornea

• Herpetic keratitis– Caused by herpes simplex virus 1 (HHV-1)– Infects cornea, may cause blindness

• Acanthamoeba keratitis– Caused by Acanthamoeba (protozoa) present in

water– Severe damage may require a corneal transplant