Microbial Diseases Vocabulary

Microbial Diseases of the Skin, Eye, and Nervous System

Introduction

• This lecture covers microbial diseases affecting the skin, eye, and nervous system.
• There are three remaining lessons in the semester, focusing on microbial diseases of the human body.
• The final exam is scheduled for May 19th, from 8:30 am to 10:30 am, in the usual lecture room.

Extra Credit Opportunity

• A total of six points can be earned towards the final grade (the final exam is 25% of the total grade).
• Submit a table covering the last three lectures of Unit 3 (lectures 10, 11, and 12).
• Three points will be awarded for including all lectures.
• Two points for organization (minimum categories required).
• One point for clarity, neatness, and conciseness.
• Categories include microbe type, species, Gram stain result, infected system, disease, symptoms, causes/source, treatment, and important notes.
• It's acceptable to leave boxes blank if the material wasn't covered.

Pathology, Infection, and Disease

• Pathology: The study of disease.
• Pathogenicity: The ability to cause disease.
• Virulence: The degree of pathogenicity.
• Infection: Invasion or colonization of the body by pathogens.
• Disease: An abnormal state in which the body is not performing normal functions.

Koch’s Postulates

• Koch’s postulates are used to prove the cause of an infectious disease. The postulates are:
  1. The same pathogen must be present in every case of the disease.
  2. The pathogen must be isolated from the diseased host and grown in pure culture.
  3. The pathogen from the pure culture must cause the disease when it’s inoculated into healthy, susceptible laboratory animals.
  4. The pathogen must be isolated from the inoculated animal and must be the originally inoculated species.
• Key concepts:
  • A specific infectious disease is caused by a specific microbe.
  • Koch's postulates help determine the etiology of disease, the first step in treatment and prevention.
  • Microbiologists use these steps to identify causes of emerging diseases.

Classifying Infectious Diseases

• Symptoms: Changes in body function that are felt by a patient as a result of disease.
• Signs: Changes in a body that can be measured or observed as a result of disease.
• Syndrome: A specific group of signs and symptoms that accompany a disease.

Examples of Signs and Symptoms

• Signs:
  • Fever
  • Septicemia
  • Microbes in tissue fluids that should be sterile
  • Abnormal chest sounds
  • Skin eruptions
  • Leukocytosis
  • Leukopenia
  • Swollen lymph nodes
  • Abscesses
  • Tachycardia (increased heart rate)
  • Antibodies in serum
• Symptoms:
  • Chills
  • Pain, irritation
  • Nausea
  • Malaise, fatigue
  • Chest tightness
  • Itching
  • Headache
  • Weakness
  • Abdominal cramps
  • Anorexia (lack of appetite)
  • Sore throat

Classifying Infectious Diseases (cont.)

• Communicable disease: A disease that is spread from one host to another.
• Contagious diseases: Diseases that are easily and rapidly spread from one host to another.
• Highly communicable disease.
• Noncommunicable disease: A disease not spread from one host to another.

Structure and Function of the Skin

• Keratin: Waterproofing protein coating outer layer of epidermis.
• Epidermis: Thin outer portion of skin; composed of layers of epithelial cells.
• Dermis: Inner, thick portion of skin; composed mainly of connective tissue, location of skin blood supply.
• Subcutaneous: Deepest layer of skin; composed of fat and connective tissue, insulates the body and absorbs shocks.

Normal Microbiota of the Skin

• Resistant to drying and high salt concentration.
• Large numbers of gram-positive cocci (Staphylococci, Micrococci).
• Areas with moisture have higher populations.
• Metabolize sweat and contribute to body odor.
• Either colonize hair follicles (folliculitis) or skin surface.
• Mostly Gram positive microbes, some yeast.

Recognizing Microbial Skin Diseases

• Vesicles: Small, fluid-filled lesions.
• Bullae: Vesicles larger than 1 centimeter in diameter.
• Macules: Flat, reddened lesions.
• Papules: Raised lesions.
• Pustules: Raised lesions with pus.
• Impetigo: Contagious red sores that break open and leave crust, appear mostly around nose and mouth.

Prominent Microbes of Skin Diseases

• Staphylococci
• Steptococci
• * Pseudomonas aeruginosa*
• Mycobacterium ulcerans

Staphylococcal Skin Infections

• Gram-positive bacteria.
• Many produce coagulase, an enzyme that clots fibrin in the blood, used to identify types of staphylococci.
• Staphylococcus epidermidis.
• Staphylococcus aureus.

Identifying Staphylococcus Infections

• Gram positive.
• Catalase positive-bubbles!
• Coagulase positive - specifically Staphylococcus aureus MSA Plate!

Staphylococcus epidermidis

• Ninety percent of normal skin microbiota.
• Typically harmless but can be opportunistic.
• Healthcare-associated pathogen.
• Produces biofilm on catheters.
• Coagulase-negative.

Staphylococcus aureus

• Carried in the nasal passages of 20% of the population.
• Golden-yellow colonies.
• Coagulase-positive.
• May produce damaging toxins and cause sepsis.
• Avoids host defenses in the skin.
• Secretes proteins and toxins that kill phagocytic cells.
• MRSA strains are antibiotic-resistant.

Key Microbe of Focus: MRSA

• Methicillin-resistant Staphylococcus aureus (MRSA).
• Strain USA100: 92% of healthcare strains.
• Strain USA300: 89% of community-acquired strains.
• MRSA is spread by direct contact with an infected wound or from contaminated hands and surfaces, usually those in healthcare settings.
• Small molecules produced by commensal Staphylococcus epidermidis disrupt formation of biofilms by Staphylococcus aureus.

Staphylococcal Skin Infections

• Folliculitis: Infections of the hair follicles.
• Sty: Folliculitis of an eyelash.
• Impetigo: Crusting (nonbullous) sores, spread by autoinoculation.
• Furuncle (boil): A type of abscess; localized region of pus surrounded by inflamed tissue.
• Carbuncle: Damage and inflammation of deep tissue from a spreading furuncle (a cluster of furuncles).
• Note: These are the most commonly associated conditions of S. aureus but can also be caused by other pathogens.

Staphylococcal Skin Infections (cont.)

• Scalded skin syndrome
  • Staphylococcal toxin spread throughout body.
  • Fever, irritation, large sheets of skin affected.
• Bullous Impetigo
  • Staphylococcal toxin released locally; broken blisters with yellow crust on face, hands, buttocks.
• Toxic shock syndrome (TSS)
  • Fever, vomiting, shock, and organ failure caused by toxic shock syndrome toxin in the bloodstream.
  • Most commonly caused by S. aureus but can be caused by other microbes.

Streptococcal Skin Infections

• Gram-positive cocci in chains.
• Produce hemolysins that lyse red blood cells.
• Beta-hemolytic streptococci often cause disease.
• Streptococci differentiated into groups A through T (based on antigenic cell wall carbohydrates).

Group A streptococci (GAS)

• Streptococcus pyogenes.
• Eighty immunological types.
• Produce virulence factors:
  • M proteins: External to the cell wall; allow adherence and immune system avoidance.
  • Hyaluronidase: Dissolves connective tissue.
  • Streptokinases: Dissolve blood clots.
• Familiar examples: strep throat, cellulitis, impetigo.

Streptococcus pyogenes

• Erysipelas
  • S. pyogenes infects the dermal layer of the skin.
  • Causes local tissue destruction and sepsis.
• Cellulitis
  • Deep infection of the skin.
  • Usually caused by skin breaks.
  • Treated with antibiotics.
  • May require skin grafts.

Streptococcus pyogenes (cont.)

• Necrotizing fasciitis (“Flesh-eating” disease)
  • Exotoxin A produced by S. pyogenes acts as a potent toxin.
  • Necrosis of subcutaneous tissue and muscle fascia.
  • Progress in hours or days
  • Very rare, may be fatal
  • Other microbes can cause necrotizing fasciitis, however S. pyogenes is the most common cause.

Infections by Pseudomonads

• Pseudomonas aeruginosa
  • Gram-negative, aerobic rod.
  • Pyocyanin produces a blue-green pus.
  • Produces exo- and endotoxins; grows in biofilms.
• Pseudomonas dermatitis
  • Self-limiting rash acquired in swimming pools (will resolve on its own).
• Otitis externa (“Swimmer’s ear”).
• Opportunistic in burn patients.
• Resistant to many antibiotics.

Buruli Ulcer

• Caused by Mycobacterium ulcerans.
• Produces the toxin mycolactone.
• Enters via a break in the skin or an insect bite.
• Causes deep, damaging ulcers; may require amputation.
• Primarily found in western and central Africa.
• Different from necrotizing fasciitis (different bacteria, signs/symptoms).
• DOI: $10.4269/ajtmh.2010.09-0256$

Acne

• Skin cells shed in the hair follicles and combine with sebum, causing blockages.
• Propionibacterium acnes (anaerobic microbe) digests sebum; fatty acids produce an inflammatory response.
• Treated with antibiotics and benzoyl peroxide to control growth.
• Part of normal skin microbiome
• Acne also contributed to by hormones (excess production of skin oils clogging pores).

Viral Diseases of the Skin

• Many are transmitted via respiratory routes and are systemic.
• Many cause problems in children and developing fetuses.
• Key topics: Warts, Smallpox, Chickenpox, Shingles, Herpes Simplex, Measles/Rubella.

Warts

• Papillomas: Small skin growths.
• Transmitted via contact (cut in the skin, close skin-to-skin contact).
• Caused by excess amounts of keratin.
• Caused by papillomavirus (more than 50 types; some cause skin and cervical cancers).
• Treated with cryotherapy, electrodesiccation, or salicylic acid.

Smallpox (Variola)

• Caused by an orthropoxvirus.
• Two forms of the disease:
  • Variola major has 20-60% mortality.
  • Variola minor has <1% mortality.
• Transmitted via the respiratory route, moves into the bloodstream and infects the skin.
• Completely eradicated from the human population by vaccination.
• Potential bioterrorism agent.

Chickenpox & Shingles

• Chickenpox (varicella)
  • Herpesvirus varicella-zoster (human herpesvirus 3).
  • Transmitted via the respiratory route.
  • Causes pus-filled vesicles.
  • Prevented by a live attenuated vaccine.
  • Breakthrough varicella can occur if previously vaccinated.
• Shingles (herpes zoster)
  • Reactivation of the latent varicella-zoster virus that moves along peripheral nerves to the skin.
  • Due to stress or lowered immunity.

Herpes Simplex

• Human herpesvirus 1 (HSV-1) and 2 (HSV-2).
• HSV-1 is spread primarily by oral or respiratory routes.
• HSV-2 is spread primarily sexually.
• Both remain latent.
• Ninety percent of the U.S. population is infected with HSV-1.
• Usually develop as cold sores or fever blisters.

Measles (Rubeola)

• Viral disease transmitted by the respiratory route.
• Cold-like symptoms, macular rash.
• Koplik’s spots (red spots on the oral mucosa opposite the molars).
• Prevented by the MMR (measles, mumps, rubella) vaccine.
• Required for children entering childcare or any public education in US schools.

Rubella

• German measles.
• Rubella virus.
• Macular rash and light fever.
• Transmitted via the respiratory route; 2- to 3-week incubation.
• Congenital rubella syndrome
  • Fetal damage, deafness, heart defects, mental retardation in 35% of cases.
  • 15% mortality within first year of life.
• Prevented by the MMR vaccine.

Fungal Diseases of Skin and Nails

• Cutaneous mycoses
  • Caused by dermatophytes
  • Genera of fungi involved: Trichophyton, Microsporum, Epidermophyton.
• Ringworm:
  • Circular rash cause by fungal infection
• Athlete's foot:
  • Fungal infection that causes an itchy, stinging, burning rash on your skin of your feet.
• Treatment is usually topical drugs (miconazole and clotrimazole).

Subcutaneous Mycoses

• Greater severity from cutaneous mycoses.
• Usually caused by fungi that inhabit the soil.
• Sporotrichosis
  • Caused by Sporothrix schenkii (dimorphic fungus).
  • Enters a wound; forms a small ulcer.
  • Treated with potassium iodide.

Candidiasis

• Candidiasis is overgrowth of Candida albicans (yeast).
• Occurs in the skin and mucous membranes of the genitourinary tract and mouth.
• Thrush: C. albicans infection of the oral cavity.
• Results when antibiotics suppress competing bacteria or a change occurs in the mucosal pH.
• Can also occur due to dramatic changes in lifestyle (environment/diet).

Infection by Animals - Scabies

• Scabies are caused by Sarcoptes scabiei mites.
• Burrow in the skin to lay eggs.
• Causes inflammatory skin lesions.
• Transmitted via intimate contact.
• Treatment with permethrin.

Infection by Animals - Pediculosis (Lice)

• Lice
  • Pediculus humanus capitis (head louse).
  • P. h. corporis (body louse).
• Feed on blood from the host.
• Lay eggs (nits) on the hair and attach to the shafts.
• Treatment with topical insecticides (permethrin or pyrethrin).
• Malathion, lindane, or ivermectin are used in cases of resistance.

Diseases of the Eye

Inflammation of Eye Membranes: Conjunctivitis

• An inflammation of the conjunctiva.
• Also called red eye or pinkeye.
• Commonly caused by Haemophilus influenzae bacterium (not associated with influenza infections).
• Also caused by adenoviruses.
• Can be caused by pseudomonads.
• Associated with unsanitary contact lenses.
• Very contagious.

Ophthalmia Neonatorum

• Caused by Neisseria gonorrhoeae.
• Large amount of pus forms; ulceration of corneas results.
• Untreated cases may lead to blindness.
• Transmitted to a newborn’s eyes during passage through the birth canal (mother with untreated gonorrhea).
• Prevented by treating a newborn’s eyes with antibiotics.

Inclusion Conjunctivitis

• Caused by Chlamydia trachomatis (bacterium that grows as an obligate intracellular parasite).
• Gram negative bacteria.
• Transmitted to a newborn’s eyes during passage through the birth canal
• Past chlamydia infections that have been treated have a reduced risk of passing it
• Treated with tetracycline.
• Spread through swimming pool water (rarely).

Trachoma

• Caused by some serotypes of Chlamydia trachomatis.
• Leading cause of blindness worldwide.
• Transmitted via hand contact or flies.
• Infection causes permanent scarring; scars abrade the cornea, leading to blindness.
• Secondary infections can also be a factor.
• Oral azithromycin are used in treatment.

Indirect Microbial Induced Eye Damage

• Sepsis: The body’s extreme reaction to an infection
  • Triggers inflammation and leaking blood vessels.
  • May cause rental hemorrhages
  • Sepsis of the eye can lead to meningitis
• Contaminated contact lenses may lead to keratits
  • Infection of the cornea
  • Showering with contact lenses risk bacteria/parasites (ameoba)

Diseases of the Nervous System

Structure & Function of the Nervous System

• Central nervous system (CNS): Brain and spinal cord.
• Peripheral nervous system (PNS): Nerves that branch from the CNS.
• Meninges protect the brain and spinal cord (the three membranes--the dura mater, arachnoid, and pia mater--that line the skull and vertebral canal and enclose the brain and spinal cord).

Nervous System Diseases: Key Terms

• Meningitis: Inflammation of the meninges.
• Encephalitis: Inflammation of the brain.
• Meningoencephalitis: Inflammation of both.
  • Bacterial Meningitis
  • Meningococcal Meningitis
  • Streptococcus Pneumoniae Meningitis
  • Listeriosis
  • Tetanus
  • Botulism
  • Leprosy
  • Poliomyelitis
  • Rabies

Bacterial Meningitis

• Initial symptoms of fever, headache, and a stiff neck; followed by nausea and vomiting.
• May progress to convulsions and coma.
• Death from shock and inflammation (due to endotoxin and cell wall release).
• Viral meningitis is more common and mild.

Neisseria Meningitidis Meningitis (Meningococcal Meningitis)

• Aerobic, gram-negative diplococcus with a capsule.
• Forty percent of people are healthy nasopharyngeal carriers.
• Begins as a throat infection, rash, and bacteremia.
• Mortality of 9-12% with antibiotic therapy; 80% without.
• Outbreaks common in dorms and military barracks.
• Vaccination protects against serogroups A, C, Y, W, and B, but not X.

Streptococcus Pneumoniae Meningitis (Pneumococcal Meningitis)

• Gram-positive, encapsulated diplococcus.
• Infection of the brain and spinal cord.
• Seventy percent of people are healthy nasopharyngeal carriers.
• Also causes pneumonia and otitis media.
• Most common in children (1 month to 4 years).
• Mortality: 8% in children, 22% in the elderly.
• Prevented by conjugated vaccine.

Listeriosis

• Caused by Listeria monocytogenes (Gram-positive rod).
• Usually foodborne and asymptomatic.
• Meningitis more common in the immunocompromised.
• Can invade the bloodstream, causing sepsis.
• Reproduces in phagocytes; spreads phagocyte-to-phagocyte.
• Infects pregnant women, crossing the placenta and leading to stillbirth.

Tetanus

• Caused by Clostridium tetani (Gram-positive, endospore-forming, obligate anaerobe).
• Grows in deep wounds with anaerobic conditions.
• Tetanospasmin neurotoxin released from dead cells enters CNS.
• Blocks the relaxation pathway in muscles, causing muscle spasms.
• Death occurs from spasms of respiratory muscles.
• Prevented by vaccination.

Botulism

• Caused by Clostridium botulinum (Gram-positive, endospore-forming, obligate anaerobe).
• Intoxication comes from ingesting the botulinum exotoxin.
• Causes flaccid paralysis.
• Death usually comes from respiratory or cardiac failure.

Incidence and Treatment of Botulism

• Improperly canned foods or exposed wounds.
• Infant botulism: C. botulinum growing in the intestines of infants due to a lack of intestinal microbiota (associated with honey).
• Wound botulism: Growth of C. botulinum in wounds.
• Treatment with respiratory assistance and antitoxins.
• Prevented with proper canning and the use of nitrites in foods.

Leprosy

• Also called Hansen’s disease.
• Caused by Mycobacterium leprae (generation time of 12 days).
• Grows in peripheral nerves and skin cells.
• Tuberculoid (neural) form: Loss of sensation in skin areas.
• Lepromatous (progressive) form: Disfiguring nodules over the body; mucous membranes are affected.
• About 100 cases per year.
• Treated with antibiotics for 6-24 months.

Poliomyelitis

• Caused by the poliovirus.
• Transmitted by the ingestion of water containing feces containing the virus.
• Initial symptoms: Sore throat and nausea.
• Viremia may occur; enters the CNS.
• One percent of cases become paralytic (destruction of motor nerve cells).
• Death from respiratory failure.
• Vaccine for all three serotypes.

Rabies

• Caused by the rabies virus (Genus Lyssavirus; bullet-shaped; single-stranded RNA; easily develops mutants).
• Usually transmitted by the saliva of an animal bite (can also cross mucous membranes).
• In the United States, silver-haired bats are the most common cause.
• Initial symptoms: Muscle spasms of the mouth and pharynx; hydrophobia.
• Very little effective treatment (Rabies immune globulin).