Chapter 21 Microbial Diseases of the Skin and Eyes.
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Transcript of Chapter 21 Microbial Diseases of the Skin and Eyes.
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