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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
Mucous Membranes
• 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
Normal Microbiota of the Skin
• Resistant to drying &
tolerant to high salt
• Gram-positive, salttolerant bacteria
– Staphylococci
– Micrococci
– Diphtheroids
• Vigorous washing can
reduce numbers, but
will not eliminate them
Figure 14.1a
Microbial Diseases of the Skin
Figure 21.2
Microbial Diseases of the Skin
• 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
Staphylococcal Skin Infections
• 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
– 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
Streptococcal Skin Infections
• Streptococcus
pyogenes =
group A betahemolytic
streptococci
• M proteins
– Antiphagocytic
– Aid adherence
for colonization
of mucous
membrane
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)
Streptococcal Skin Infections
• 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
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 fasciitis
Figure 21.8
Infections by Pseudomonads
• 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
• 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
Acne
• 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
– 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
• Antibiotics
teratogenic)
– 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
• 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)
Figure 21.10a
Shingles
• 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
Figure 21.10b
Herpes simplex virus (HSV)
• 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
• 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 (Rubeola)
• 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)
Figure 21.13
Rubella (German Measles)
•
•
•
•
•
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
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
Cutaneous mycoses
• 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
Subcutaneous 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)
Candidiasis
• 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
Figure 21.17
Parasitic infections of the Skin: Scabies
• Tiny mite Sarcoptes scabiei burrows in the skin
to lay eggs
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
Pediculosis (lice)
– Head louse has
especially adapted
legs to grasp scalp
hairs
– Treatment with
topical insecticides
– Combing out the nits
with fine-toothed
louse combs
Figure 21.19
Microbial Diseases of the Eye
• 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
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
Bacterial Diseases of the Eye
– 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
Other Infectious 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
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 Review
2. 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 Review
3. 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