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Microbial Diseases of the Skin and Eyes


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Title: Microbial Diseases of the Skin and Eyes

Chapter 21 and 22
  • Microbial Diseases of the Skin and Eyes
  • Microbial Diseases of the Nervous System

  • Epidermis -the outer portion of the skin
  • contains keratin, a waterproof coating.
  • hair follicles
  • oil glands
  • Dermis - the inner portion of the skin
  • sweat ducts
  • Provide passageways for microorganisms.

Figure 21.1
  • Sebum and perspiration are secretions of the skin
    that can inhibit the growth of microorganisms.
  • Salt inhibits microbes
  • Lysozyme hydrolyzes peptidoglycan
  • Fatty acids inhibit some pathogens
  • Sebum and perspiration provide nutrients for some

Mucous Membranes
  • Line body cavities
  • Epithelial cells attached to an extracellular
  • Cells secrete mucus
  • Some have cilia

Microbial Diseases of the Skin
Microbial Diseases of the Skin
Vesicles are small fluid-filled lesions
bullae are vesicles larger than 1 cm
pustules are raised lesions containing pus
macules are flat, reddened lesions
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

Normal Microbiota of the Skin
  • Gram-positive, salt-tolerant bacteria
  • Staphylococcus
  • Micrococcus
  • Members of the genus Propionibacterium
  • metabolize oil from the oil glands
  • colonize hair follicles.
  • Malassezia furfur yeast
  • grows on oily secretions and may be the cause of
  • The normal skin microbiota are not completely
    removed by washing.
  • Bacterial pathogens
  • Staphilococcus aureus
  • Streptococcus pyogenes
  • Pseudomonas aeruginosa
  • Propionibacterium acnes

Figure 14.1a
Staphylococcal Skin Infections
  • The majority of skin microbiota consist of
    Staphylococcus epidermidis
  • coagulase-negative
  • Almost all pathogenic strains of S. aureus
  • Coagulase, form fibrin clots, protected from
  • Enterotoxins, affect the GIT
  • leukocidins,
  • exfoliative toxin.
  • penicillinase
  • these are treated with vancomycin.

Staphylococcal Skin Infections
  • Localized infections
  • Folliculitis (sties, pimples, and carbuncles)
    result from S. aureus entering natural openings
    in the skin hair follicle
  • Impetigo of the newborn
  • highly contagious superficial skin infection
  • caused by S. aureus.
  • Toxemia occurs when toxins enter the bloodstream
  • Scalded skin syndrome
  • Toxic shock syndrome

Figure 21.4
Streptococcal Skin Infections
  • Streptococcus are gram-positive cocci classified
    according to their hemolytic enzymes and cell
    wall antigens.
  • Group A beta-hemolytic streptococci (including
    Streptococcus pyogenes) are the pathogens most
    important to humans.
  • Produce a number of virulence factors
  • M protein,
  • erythrogenic toxin,
  • deoxyribonuclease,
  • streptokinases,
  • hyaluronidase.

Figure 21.5
Streptococcal Skin Infections
  • Erysipelas
  • infects the dermal layer
  • reddish patches
  • Can progress to local tissue destruction
  • Enter the bloodstream
  • Impetigo
  • isolated pustules
  • Streptococcal toxic shock syndrome
  • Cellulitis, myositis and necrotizing fasciitis

Figure 21.6, 7
Infections by Pseudomonads
  • Pseudomonads are gram-negative rods.
  • Aerobes found primarily in soil and water that
  • resistant to many disinfectants and antibiotics.
  • Pseudomonas aeruginosa produces an endotoxin and
    several exotoxins.
  • Cause otitis externa,
  • respiratory infections,
  • burn infections,
  • dermatitis.
  • Infections have a characteristic blue-green pus
    caused by the pigment pyocyanin.
  • Quinolones are useful in treating P. aeruginosa

What was the mostly likely source of this
outbreak of Pseudmonas dermatitis?
  • Comedonal acne
  • Occurs when sebum channels are blocked with shed
  • Inflammatory acne
  • Propionibacterium acnes
  • Gram-positive, anaerobic rod
  • Treatment
  • Preventing sebum formation (isotretinoin)
  • Antibiotics
  • Benzoyl peroxide to loosen clogged follicles
  • Visible (blue) light (kills P. acnes)
  • Nodular cystic acne
  • Treatment isotretinoin

Viral Diseases of the Skin - Warts
  • Papillomaviruses cause skin cells to proliferate
    and produce a benign growth called a wart or
  • Warts are spread by direct contact.
  • Warts may regress spontaneously or be removed
    chemically or physically.
  • Interferon gamma

Viral Diseases of the Skin Poxviruses
  • Smallpox (Variola) virus causes two types of skin
    infections variola major and variola minor.
  • Smallpox is transmitted by the respiratory route,
    and the virus is moved to the skin via the
  • The only host for smallpox is humans.
  • Smallpox has been eradicated as a result of a
    vaccination effort by the WHO

Figure 21.9
Viral Diseases of the Skin Herpesviruses
  • Varicella-zoster virus is transmitted by the
    respiratory route and is localized in skin cells,
    causing pus-filled vesicles.
  • Complications of chickenpox include encephalitis
    and Reyes syndrome.
  • After chickenpox, the virus can remain latent in
    nerve cells and subsequently activate as shingles.

Figure 21.10a
  • Reactivation of latent varicella-zoster virus
    releases viruses that move along peripheral
    nerves to skin.
  • Shingles (herpes zoster) is characterized by a
    vesicular rash along the affected cutaneous
    sensory nerves.
  • The virus can be treated with acyclovir.
  • An attenuated live vaccine is available.

Figure 21.10b
Herpes simplex 1 and Herpes simplex 2
  • Herpes simplex infection of mucosal cells results
    in cold sores and occasionally encephalitis.
  • HSV-1 is transmitted primarily by oral and
    respiratory routes.
  • The virus remains latent in nerve cells, and cold
    sores can recur when the virus is activated.
  • Herpes encephalitis occurs when herpes simplex
    viruses infect the brain.
  • Acyclovir has proven successful in treating
    herpes encephalitis.

Measles (Rubeola)
  • Measles is caused by measles virus and
    transmitted by the respiratory route.
  • Vaccination provides effective long-term
  • After the virus has incubated in the upper
    respiratory tract, macular lesions appear on the
    skin, and Kopliks spots appear on the oral
  • Complications of measles include middle ear
    infections, pneumonia, encephalitis, and
    secondary bacterial infections.

Figure 21.14
Rubella (German Measles)
  • The rubella virus is transmitted by the
    respiratory route.
  • A red rash and light fever might occur in an
    infected individual the disease can be
  • Congenital rubella syndrome can affect a fetus
    when a woman contracts rubella during the first
    trimester of her pregnancy.
  • Damage from congenital rubella syndrome includes
    stillbirth, deafness, eye cataracts, heart
    defects, and mental retardation.
  • Vaccination with live rubella virus provides
    immunity of unknown duration.

Figure 21.15
Fungal Diseases of the Skin and Nails - Cutaneous
  • Fungi that colonize the outer layer of the
    epidermis cause dermatomycoses called ringworm,
    or tinea
  • Microsporum,
  • Trichophyton,
  • Epidermophyton cause dermatomycoses.
  • These fungi grow on keratin-containing epidermis,
    such as hair, skin, and nails.
  • Ringworm and athletes foot are usually treated
    with topical antifungal chemicals.
  • Diagnosis is based on the microscopic examination
    of skin scrapings or fungal culture.
  • Oral griseofulvin
  • Topical miconazole

Cutaneous Mycoses
Figure 21.16
Subcutaneous Mycoses
  • Sporotrichosis results from a soil fungus that
    penetrates the skin through a wound.
  • The fungi grow and produce subcutaneous nodules
    along the lymphatic vessels.

  • C. albicans is an opportunistic pathogen that may
    proliferate when the normal bacterial microbiota
    are suppressed.
  • Candida albicans (yeast) causes infections of
    mucous membranes and is a common cause of thrush
    (in oral mucosa) and vaginitis.
  • Topical antifungal chemicals may be used to treat
  • miconazole or nystatin

Microbial Diseases of the Eye
  • The mucous membrane lining the eyelid and
    covering the eyeball is the conjunctiva.
  • Inflammation of the Eye Membranes
  • Conjunctivitis is caused by several bacteria and
    can be transmitted by improperly disinfected
    contact lenses.

Microbial Diseases of the Eye
  • Conjunctivitis (pinkeye)
  • Haemophilus influenzae
  • Various microbes
  • Associated with unsanitary contact lenses
  • Neonatal gonorrheal ophthalmia
  • Neisseria gonorrhoeae
  • Transmitted to newborn's eyes during passage
    through the birth canal
  • Prevented by treatment newborn's eyes with

Microbial Diseases of the Eye
  • Chlamydia trachomatis
  • Inclusion conjunctivitis
  • Transmitted to newborn's eyes during passage
    through the birth canal
  • Spread through swimming pool water
  • Treated with tetracycline
  • Trachoma (caused by certain serotipes of
    Chlamydia trachomatis)
  • Greatest cause of blindness worldwide
  • Infection causes permanent scarring scars abrade
    the cornea leading to blindness

Microbial Diseases of the Eye
  • 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

Learning objectives
  • Describe the structure of the skin and mucous
    membranes and the ways pathogens can invade the
  • Provide examples of normal skin microbiota, and
    state their locations and ecological roles of its
  • Differentiate staphylococci from streptococci,
    and name several skin infections caused by each.
  • List the causative agent, method of transmission,
    and clinical symptoms of Pseudomonas, dermatitis,
    otitis externa, acne.
  • List the causative agent, method of transmission,
    and clinical symptoms of these skin infections
    warts, smallpox, chickenpox, shingles, cold
    sores, measles, rubella.
  • Differentiate cutaneous from subcutaneous
    mycoses, and provide an example of each.
  • List the causative agent of and predisposing
    factors for candidiasis.
  • Define conjunctivitis.
  • List the causative agent, method of transmission,
    and clinical symptoms of these eye infections
    neonatal gonorrheal ophthalmia, inclusion
    conjunctivitis, trachoma.
  • List the causative agent, method of transmission,
    and clinical symptoms of these eye infections
    herpetic keratitis, Acanthamoeba keratitis.

The Nervous System
  • The central nervous system (CNS) consists of
  • the brain, which is protected by the skull bones
  • the spinal cord, which is protected by the
  • The peripheral nervous system (PNS) consists of
    the nerves that branch from the CNS.

  • The CNS is covered by three layers of membranes
    called meninges
  • dura mater,
  • arachnoid mater
  • pia mater.
  • Cerebrospinal fluid (CSF) circulates between the
    arachnoid mater and the pia mater in the
    subarachnoid space.

Blood-brain barrier
Structure and Function of the Nervous System
  • The bloodbrain barrier normally prevents many
    substances, including antibiotics, from entering
    the brain.
  • Microorganisms can enter the CNS through
  • trauma
  • along peripheral nerves
  • through the bloodstream and lymphatic system.
  • An infection of the meninges is called
  • An infection of the brain is called

Bacterial Diseases of the Nervous System
  • Meningitis can be caused by viruses, bacteria,
    fungi, and protozoa.
  • Bacterial Meningitis 
  • Nearly 50 species of opportunistic bacteria can
    cause meningitis.
  • The three major causes of bacterial meningitis
  • Haemophilus influenzae
  • Part of the normal throat microbiota.
  • Requires blood factors for growth
  • A conjugated vaccine directed against the
    capsular polysaccharide antigen is available.
  • Neisseria meningitidis
  • This bacterium is found in the throats of
    healthy carriers.
  • Symptoms are due to endotoxin.
  • The bacteria probably gain access to the meninges
    through the bloodstream.
  • Purified capsular polysaccharide vaccine against
    serotypes A, C, Y, and W-135 is available.
  • Streptococcus pneumoniae
  • commonly found in the nasopharynx.
  • It is rare disease but has a high mortality rate.
  • A conjugated vaccine is available.

Diagnosis and Treatment of the Most Common Types
of Bacterial Meningitis
  • Diagnosis is based on Gram stain and serological
    tests of the bacteria in CSF.
  • Cultures are usually made on blood agar and
    incubated in an atmosphere containing reduced
    oxygen levels.
  • Cephalosporins may be administered before
    identification of the pathogen.

  • Tetanus is caused by a localized infection of a
    wound by Clostridium tetani.
  • C. tetani produces the neurotoxin tetanospasmin,
    which causes the symptoms of tetanus spasms,
    contraction of muscles controlling the jaw, and
    death resulting from spasms of respiratory
  • C. tetani is an anaerobe that will grow in deep,
    unclean wounds and wounds with little bleeding.
  • Acquired immunity results from DPT immunization
    that includes tetanus toxoid.
  • Following an injury, an immunized person may
    receive a booster of tetanus toxoid. An
    unimmunized person may receive (human) tetanus
    immune globulin.
  • Debridement (removal of tissue) and antibiotics
    may be used to control the infection.

Figure 22.6
  • Botulism is caused by an exotoxin produced by
    Clostridium botulinum growing in foods.
  • The toxin is a neurotoxin that inhibits the
    transmission of nerve impulses. Blurred vision
    occurs in 1 to 2 days progressive flaccid
    paralysis follows for 1 to 10 days, possibly
    resulting in death from respiratory and cardiac
  • C. botulinum will not grow in acidic foods or in
    an aerobic environment.
  • Endospores are killed by proper canning. The
    addition of nitrites to foods inhibits growth
    after endospore germination.
  • The toxin is heat labile and is destroyed by
    boiling (100C) for 5 minutes.
  • Infant botulism results from the growth of C.
    botulinum in an infants intestines.
  • Wound botulism occurs when C. botulinum grows in
    anaerobic wounds.
  • For diagnosis, mice protected with antitoxin are
    inoculated with toxin from the patient or foods.

  • Mycobacterium leprae
  • Acid-fast rod that grows best at 30C
  • Grows in peripheral nerves and skin cells
  • Transmission requires prolonged contact with an
    infected person
  • Tuberculoid (neural) form Loss of sensation in
    skin areas positive lepromin test
  • Lepromatous (progressive) form Disfiguring
    nodules over body negative lepromin test
  • Untreated individuals often die of secondary
    bacterial complications, such as tuberculosis.
  • Patients with leprosy are made noncontagious
    within 4 to 5 days with sulfone drugs and then
    treated as outpatient.

Figure 22.8
  • Poliovirus
  • Transmitted by ingestion
  • Initial symptoms sore throat and nausea
  • Viremia may occur
  • If persistent, virus can enter the CNS
    destruction of motor cells and paralysis occurs
  • Diagnostics of polio is based on isolation of the
    virus and neasured of cytopatic effect on the
  • Prevention is by vaccination (enhanced-inactivated
    polio vaccine)

Rabies virus (Rhabdovirus)
Rabies virus causes an acute, usually fatal,
encephalitis called rabies. Encephalitis occurs
when the virus moves along peripheral nerves to
the CNS.
Figure 22.11
Rabies virus (Rhabdovirus)
  • Transmitted by animal bite
  • Virus multiplies in skeletal muscles, then brain
    cells causing encephalitis
  • Initial symptoms may include muscle spasms of the
    mouth and pharynx and hydrophobia
  • Furious rabies animals are restless then highly
  • Paralytic rabies animals seem unaware of
  • Preexposure prophylaxis Infection of human
    diploid cells vaccine
  • Postexposure treatment Vaccine immune globulin

Rabies virus (Rhabdovirus)
Figure 22.12
Arboviral Encephalitis
  • Arboviruses are arthropod-borne viruses that
    belong to several families transmitted by
    mosquitoes cause encephalitis.
  • Symptoms of encephalitis are chills, headache,
    fever, and eventually coma.
  • The incidence of arboviral encephalitis increases
    in the summer months, when mosquitoes are most
  • Diagnosis is based on serological tests.
  • Control of the mosquito vector is the most
    effective way to control encephalitis.

Fungal Disease of the Nervous System
  • Cryptococcus neoformans Meningitis
  • an encapsulated yeastlike fungus that causes
  • The disease may be contracted by inhalation of
    dried infected pigeon or chicken droppings.
  • The disease begins as a lung infection and may
    spread to the brain and meninges.
  • Immunosuppressed individuals are most susceptible
    to Cryptococcus neoformans meningitis.
  • Diagnosis is based on latex agglutination tests
    for cryptococcal antigens in serum or CSF.

Protozoan Diseases of the Nervous System
  • African Trypanosomiasis  is caused by the
    protozoa Trypanosoma brucei gambiense and T. b.
    rhodesiense and transmitted by the bite of the
    tsetse fly.
  • The disease affects the nervous system of the
    human host, causing lethargy and eventually coma.
    It is commonly called sleeping sickness.
  • Vaccine development is hindered by the
    protozoans ability to change its surface
  • Amebic Meningoencephalitis 
  • Encephalitis caused by the protozoan Naegleria
    fowleri is almost always fatal.
  • Granulomatous amebic encephalitis,
  • caused by Acanthamoeba spp. and Balamuthia
    mandrillaris, is a chronic disease.

Nervous System Diseases Caused by Prions
  • Prions are self-replicating proteins with no
    detectable nucleic acid.
  • Diseases of the CNS that progress slowly and
    cause spongiform degeneration are caused by
  • Sheep scrapie and bovine spongiform
    encephalopathy (BSE) are examples of diseases
    caused by prions that are transferable from one
    animal to another.
  • Creutzfeldt-Jakob disease and kuru are human
    diseases similar to scrapie. They are transmitted
    between humans.

Transmissible Spongiform Encephalopathies
Figure 22.17a
Learning objectives
  • Define central nervous system and blood-brain
  • Differentiate meningitis from encephalitis.
  • Discuss the epidemiology of meningitis caused by
    H. influenzae, S. pneumoniae, N. meningitidis,
    and L. monocytogenes.
  • Explain how bacterial meningitis is diagnosed and
  • Discuss the epidemiology of tetanus, including
    mode of transmission, etiology, disease symptoms,
    and preventive measures.
  • State the causative agent, symptoms, suspect
    foods, and treatment for botulism.
  • Discuss the epidemiology of leprosy, including
    mode of transmission, etiology, disease symptoms,
    and preventive measures.
  • Discuss the epidemiology of poliomyelitis,
    rabies, and arboviral encephalitis, including
    mode of transmission, etiology, and disease
  • Compare preexposure and postexposure treatments
    for rabies.
  • Explain how arboviral encephalitis can be
  • Identify the causative agent, reservoir,
    symptoms, and treatment for cryptococcosis.
  • Identify the causative agent, vector, symptoms,
    and treatment for African trypanosomiasis and
    amebic meningoencephalitis.
  • List the characteristics of diseases caused by
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