Title: Microbial Diseases of the Skin and Eyes
1Chapter 21 and 22
- Microbial Diseases of the Skin and Eyes
- Microbial Diseases of the Nervous System
2Skin
- 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
3Skin
- 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.
4Mucous Membranes
- Line body cavities
- Epithelial cells attached to an extracellular
matrix - Cells secrete mucus
- Some have cilia
5Microbial 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
6Microbial Diseases of the Skin
- Exanthem
- Skin rash arising from another focus of infection
- Enanthem
- Mucous membrane rash arising from another focus
of infection
7Normal 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
8Staphylococcal 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.
9Staphylococcal 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
10Streptococcal 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
11Streptococcal 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
12Infections 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.
13What was the mostly likely source of this
outbreak of Pseudmonas dermatitis?
14Acne
- 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
15Viral 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
16Viral 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
17Viral 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
18Shingles
- 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
19Herpes 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.
20Measles (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
21Rubella (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
22Fungal 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
23Cutaneous Mycoses
Figure 21.16
24Subcutaneous 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.
25Candidiasis
- 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
26Microbial 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.
27Microbial 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
28Microbial 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
29Microbial 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
30Learning 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.
31The 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.
32CNS
- 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.
33Blood-brain barrier
34Structure 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.
35Bacterial 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.
36Diagnosis 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.
37Tetanus
- 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.
38Tetanus
Figure 22.6
39Botulism
- 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.
40Leprosy
- 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.
41Leprosy
Figure 22.8
42Poliomyelitis
- 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)
43Rabies 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
44Rabies 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
45Rabies virus (Rhabdovirus)
Figure 22.12
46Arboviral 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.
47Fungal 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.
48Protozoan 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.
49Nervous 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.
50Transmissible Spongiform Encephalopathies
Figure 22.17a
51Learning 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.