Microbial Diseases of the Skin and Eyes

1
Chapter 21 and 22

• Microbial Diseases of the Skin and Eyes
• Microbial Diseases of the Nervous System

2
Skin

• 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
3
Skin

• 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
  microorganisms.

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Mucous Membranes

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

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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
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Microbial Diseases of the Skin

• Exanthem
• Skin rash arising from another focus of infection
• Enanthem
• Mucous membrane rash arising from another focus
  of infection

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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
  dandruff.
• The normal skin microbiota are not completely
  removed by washing.
• Bacterial pathogens
• Staphilococcus aureus
• Streptococcus pyogenes
• Pseudomonas aeruginosa
• Propionibacterium acnes

Figure 14.1a
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Staphylococcal Skin Infections

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

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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
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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
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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
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Infections by Pseudomonads

• Pseudomonads are gram-negative rods.
• Aerobes found primarily in soil and water that
  are
• 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
  infections.

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What was the mostly likely source of this
outbreak of Pseudmonas dermatitis?
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Acne

• Comedonal acne
• Occurs when sebum channels are blocked with shed
  cells
• 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

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Viral Diseases of the Skin - Warts

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

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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
  bloodstream.
• The only host for smallpox is humans.
• Smallpox has been eradicated as a result of a
  vaccination effort by the WHO

Figure 21.9
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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
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Shingles

• 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
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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.

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Measles (Rubeola)

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

Figure 21.14
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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
  asymptomatic.
• 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
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Fungal Diseases of the Skin and Nails - Cutaneous
Mycoses

• 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

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Cutaneous Mycoses
Figure 21.16
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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.

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Candidiasis

• 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
  candidiasis.
• miconazole or nystatin

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Microbial Diseases of the Eye

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

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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
  antibiotics

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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

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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

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Learning objectives

• Describe the structure of the skin and mucous
  membranes and the ways pathogens can invade the
  skin.
• Provide examples of normal skin microbiota, and
  state their locations and ecological roles of its
  members.
• 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.

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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
  backbone.
• The peripheral nervous system (PNS) consists of
  the nerves that branch from the CNS.

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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.

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Blood-brain barrier
34
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
  meningitis.
• An infection of the brain is called
  encephalitis.

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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
  are
• 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.

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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.

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Tetanus 

• 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
  muscles.
• 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.

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Tetanus
Figure 22.6
39
Botulism

• 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
  failure.
• 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.

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Leprosy

• 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.

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Leprosy
Figure 22.8
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Poliomyelitis

• 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
  in
• Diagnostics of polio is based on isolation of the
  virus and neasured of cytopatic effect on the
  cells.
• Prevention is by vaccination (enhanced-inactivated
  polio vaccine)

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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
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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
  excitable
• Paralytic rabies animals seem unaware of
  surroundings
• Preexposure prophylaxis Infection of human
  diploid cells vaccine
• Postexposure treatment Vaccine immune globulin

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Rabies virus (Rhabdovirus)
Figure 22.12
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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
  numerous.
• Diagnosis is based on serological tests.
• Control of the mosquito vector is the most
  effective way to control encephalitis.

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Fungal Disease of the Nervous System

• Cryptococcus neoformans Meningitis
• an encapsulated yeastlike fungus that causes
  cryptococcosis.
• 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.

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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
  antigens.
• 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.

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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
  prions.
• 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.

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Transmissible Spongiform Encephalopathies
Figure 22.17a
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Learning objectives

• Define central nervous system and blood-brain
  barrier.
• 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
  treated.
• 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
  symptoms.
• Compare preexposure and postexposure treatments
  for rabies.
• Explain how arboviral encephalitis can be
  prevented.
• 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
  prions.