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
Keratins - a waterproof coating
Hair follicles
Oil glands
Dermis - the inner portion of the skin
Sweat ducts
Provide passageways for microorganisms.
Sebum and perspiration are secretions of the skin
Can inhibit the growth of microorganisms
Salt inhibits microbes
Lysozyme hydrolyzes peptidoglycan
Fatty acids inhibit some pathogens
Provide nutrients for some microorganisms.
Figure 21.1

3. Mucous Membranes Line body cavities
Epithelial cells attached to an extracellular matrix
Cells secrete mucus ( often acidic)
Some have cilia

4. 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

5. Microbial Diseases of the Skin
Many diseases manifested by skin lesions are actually systemic diseases affecting internal organs
Exanthem (from Greek "exanthema", a breaking out)
Skin rash arising from another focus of infection
Enanthem (ulcerative lesions on oropharyngeal mucosa)
Mucous membrane rash arising from another focus of infection
Vesicles are small fluid-filled lesions
Bullae are vesicles larger than 1 cm
Macules are flat, reddened lesions
Pustules are raised lesions containing pus
Figure 21.2

6. 1. Staphylococcal Skin Infections
Gram-positive bacteria in irregular grape like clusters
1. Coagulase-negative
Staphylococcus epidermidis
-make up 90% of normal flora on skin
-can cause severe infections in those with venous catheters and
immune-suppressed patients.
2. Coagulase-positive
Staphylococcus aureus
- resident of nasal passage
- can survive on dry surfaces for months
- often evade host defenses
Almost all pathogenic strains of S. aureus produce:
Coagulase positive ( form fibrin clots, protected from phagocytosis), Enterotoxins, affect the GIT, Leukocidins ,Exfoliative toxin
Lysozyme resistant, Superantigen, Penicillinase
these are treated with vancomycin.

7. Staphylococcal Skin Infections
Can cause…
- folliculitis, furuncle, carbuncle, impetigo
scalded skin syndrome
life threatening sepsis
toxic shock syndrome

8. 2. 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:
Hemolysins
Deoxyribonuclease
Streptokinases
Hyaluronidase
M protein
Figure 21.5

9. 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
M proteins
Complex with fibrinogen
Binds to neutrophils
Activates neutrophils
Release of damaging enzymes
Shock and organ damage
Figure 21.6, 7

10. 3. 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:
dermatitis
otitis externa
burn infections
respiratory infections
Infections have a characteristic blue-green pus caused by the pigment pyocyanin.
Quinolones are useful in treating P. aeruginosa infections.

11. What was the mostly likely source of this outbreak of Pseudmonas dermatitis?
Exposure
Relative Risk
Restaurant
1.24
Arcade
1.04
Swimming pool
6.14
Exercise room
1.29
Hot tub
9.90

12. Acne Comedonal (mild) acne
Occurs when sebum channels are blocked with shed cells
Inflammatory (moderate) acne
The microorganism responsible for acne is Propionibacterium.
Gram positive
Obligate anaerobic
Slow growing
Rod shaped or branched
Produce lactic acid propionic acid and acetic acid from glucose
Treatment
over the counter products (mild soaps, sulfur, benzyl peroxide)
prescription topical (topical antibiotics, topical retinoid, acanya, benzaclin, differin)
oral medications (oral contraceptives, minocycline, doxycycline)
-professional procedures (microdermabrasion, blue light therapy, facials, chemical peels)
Nodular cystic (severe) acne
Treatment: isotretinoin

13. Viral Diseases of the Skin
Papillomaviruses cause skin cells to proliferate and produce a benign growth called a wart or papilloma.
dsDNA viruses
Productive infections only in the stratified epithelium of the skin or mucous membranes
Warts are spread by direct contact with the virus
Warts may regress spontaneously or be removed chemically or physically.
Interferon gamma

14. 3. Poxviruses
Smallpox (Variola) virus causes two types of skin infections: variola major and variola minor.
Very high infectious nature; virus particles needed.
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.
Symptoms - flu like symptoms; fever, body aches, headache, chills, backache, confusion.
Virus infects internal organs, bloodstream, and epidermal layer of the skin.
30% of patients die within two weeks. Smallpox lives scarred skin. blindness, arthritis, bone infection, lethal to a fetus.
Treatment- no cure.
Smallpox has been eradicated as a result of a vaccination effort by the WHO. popular in 1970s
Vaccination is a life variola virus administered under the skin, leaves a scar and can spread while it heals.
Possible damage of the vaccine and death.

15. 3. Herpesviruses: 3.1. Chicken Pox and Shingles
Varicella zoster virus (Human Herpervirus 3 )
Belongs to a group of eight herpes viruses that infect humans
Very susceptible to disinfectants
Infection originally occurs via droplet transmission and
incubates in respiratory epithelium for days
After primary infection, Varicella zoster virus remains dormant in sensory nerve roots latent for a long period of time.
Can be reactivated as Herpes zoster to cause shingles later in
life if the immune system is compromised.
Symptoms:
Red itchy rash of blisters filled with fluid, Mild fever,
Backache, Headache, Sore throat
Treatment:
Live attenuated Varicella vaccine is available and suggested.
Antiviral medication may be prescribed for high risk cases. Usually just pain medication and/or anti-histamines for itching and time is all that is necessary. (aspirin should not be taken as it can lead to Reye’s Syndrome)

16. 3.2. 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.

17. 4. Measles (Rubeola) Caused by measles virus
Transmitted by the respiratory route.
Extremely contagious viral disease spread by the respiratory route
Koplik’s spots
Small red spots with central blue-white specks
Diagnostic indicator of disease
MMR vaccine
Vaccine is 95% effective
Children under 1 are at risk
Complications of measles include middle ear infections, pneumonia, encephalitis, and secondary bacterial infections.

18. 5. Rubella (German Measles)
The rubella viruses 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.

19. Fungal Diseases of the Skin and Nails
1. 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 athlete’s foot are usually treated with topical antifungal chemicals.
Diagnosis is based on the microscopic examination of skin scrapings or fungal culture.
Treatment
Oral griseofulvin
Topical miconazole

20. 2. Subcutaneous Mycoses 3. Candidiasis
More serious than cutaneous 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.
Most common U.S. disease of this type
Sporothrix schenchii enters puncture wound
Treated with potassium iodide (KI)
3. Candidiasis
Candida albicans is an opportunistic pathogen that may proliferate when the normal bacterial microbiota are suppressed.
C. 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

21. Eyes Conjunctiva (Mucous membrane) Lacrimal apparatus –
Lines the inside of the eyelids and covers the sclera (white part of the eye)
Composed of non-keratinized epithelium
Secrete mucus and the aqueous portion of tears
Contains blood vessels, fibrous tissue, and lymphatic channels
Lacrimal apparatus –
Tear production and drainage
Anti-microbial compounds
Lysozyme
Secretory antibodies (IgA).

22. Microbial Diseases of the Eye
Conjunctivitis (pinkeye)
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.
Haemophilus influenzae
Various microbes
Associated with unsanitary contact lenses

23. Microbial Diseases of the Eye
2. Neonatal gonorrheal ophthalmia
Neisseria gonorrhoeae
Transmitted to newborn's eyes during passage through the birth canal
Prevented by treatment newborn's eyes with antibiotics
3. Trachoma (caused by certain serotypes of Chlamydia trachomatis)
Inclusion conjunctivitis
Spread through swimming pool water
Treated with tetracycline
Greatest cause of blindness worldwide
Infection causes permanent scarring; scars abrade the cornea leading to blindness
4. Herpetic Keratitis
Herpes simplex virus 1 (HHV-1)
Infects cornea, may cause blindness
Treated with trifluridine
5. Acanthamoeba keratitis
Transmitted from water
Associated with unsanitary contact lenses

24. 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.

25. The Nervous System The central nervous system (CNS)
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.
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.

26. Structure and Function of the Nervous System
The blood–brain 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.
Meningitis -An infection of the meninges.
Meningitis can be caused by viruses, bacteria, fungi, and protozoa.
Encephalitis - An infection of the brain.
Primary encephalitis - caused by a bacterial infection such as bacterial meningitis spreading directly to the brain
Secondary encephalitis - a complication of a current infectious disease (syphilis)

27. Bacterial Meningitis 
Nearly 50 species of opportunistic bacteria can cause meningitis.
Symptoms-fever, headache and stiff neck, nausea and vomiting, neurological damage, may progress to convulsions, coma , death.
The three major causes of bacterial meningitis are:
1. Haemophilus influenzae
Part of the normal throat microbiota.
Requires blood factors for growth;
A conjugated vaccine directed against the capsular polysaccharide antigen is available.
2. 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.
3. Streptococcus pneumoniae
commonly found in the nasopharynx.
It is rare disease but has a high mortality rate.
A conjugated vaccine is available.

28. 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.

29. Genus Clostridium Clostridium tetani
1. Tetanus
Clostridium tetani
Obligate anaerobe
Endospore-forming
Produces the neurotoxin tetanospasmin,
Tetanus bacilli live in the soil, so the most dangerous kind of injury involves possible contamination with dirt, animal feces, and manure, self-piercing
Tetanus is not spread from person to person.
Causes localized infection of a wound ( grow in deep, unclean wounds and wounds with little bleeding)
Symptoms: spasms, contraction of muscles controlling the jaw, and death resulting from spasms of respiratory muscles.
Acquired immunity results from DPT immunization (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.

30. - Clostridium botulinum
2. Botulism
- Clostridium botulinum
Anaerobe
Growing in foods.
Produced a neurotoxin that inhibits the transmission of nerve impulses.
Symptoms: 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.
Several serological types of botulinal toxin - differed in their virulence
The toxin is heat labile and is destroyed by boiling (100°C) for 5 minutes.
Endospore-forming
Killed by proper canning.
The addition of nitrites to foods inhibits growth after endospore germination.
C. botulinum will not grow in acidic foods or in an aerobic environment.
Infant botulism results from the growth of C. botulinum in an infant’s 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.

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

32. Viral disease of the Nervous System
1. Rabies - Rabies virus (Rhabdovirus)
Transmitted by animal bite (zoonotic)
Virus multiplies in skeletal muscles,
then brain cells causing encephalitis
An acute, usually fatal encephalitis
Occurs when the virus moves
along peripheral nerves to the CNS.
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
Pre exposure prophylaxis: Infection of human diploid cells vaccine
Post exposure treatment: Vaccine + immune globulin

33. 2. Poliomyelitis - Poliovirus
Transmitted by ingestion
Initial symptoms: sore throat and nausea
Viremia (presence of a virus in the blood) may occur;
If persistent, virus can enter the CNS; destruction of motor cells and paralysis occurs in <1% of cases
Diagnostics of polio is based on isolation of the virus and measured of cytopatic effect on the cells.
Prevention is by vaccination (enhanced-inactivated polio vaccine)
3. 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.

34. Fungal Disease of the Nervous System
Cryptococcus neoformans meningitis
an encapsulated yeast like 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.

35. Protozoan Diseases of the Nervous System
1. African Trypanosomiasis 
Causative agent - Trypanosoma brucei gambiense and T. b. rhodesiense
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 protozoan’s ability to change its surface antigens.
2. Amebic Meningoencephalitis 
Encephalitis caused by the protozoan Naegleria fowleri is almost always fatal.
3. Granulomatous amebic encephalitis
Caused by Acanthamoeba spp. and Balamuthia mandrillaris, is a chronic disease.

36. Transmissible Spongiform Encephalopathies
Causative agent – prions
Tiny holes appear in the cortex causing it to appear
like a sponge (hence 'spongiform') when brain tissue
obtained at autopsy is examined under a microscope
A group of progressive conditions that affect the brain and nervous system of animals and also humans.
The disorders cause impairment of brain function, including memory changes, personality changes and problems with movement that worsen over time.
Prion diseases of humans include classic
Mad cow disease, Sheep scrapie and bovine spongiform encephalopathy (BSE) are transferable from one animal to another
Creutzfeldt-Jakob disease and kuru are human diseases similar to scrapie. They are transmitted between humans.
Figure 22.17a

37. 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.