Unit 13: Microbial Diseases; Lesson 1: Microbial Diseases of the Skin and Eyes

Pimples

Etiologic Agent: -Staphylococcus aureus Clinical Symptoms: -Infected hair follicles Mode of transmission: -Direct Contact

*What bacteria are identified by a positive coagulase test? What bacteria are characterized as group A beta-hemolytic

Staphylococcus aureus- COAGULASE- POSITIVE Streptococcus pyogenes-group A beta-hemolytic

*Define conjunctivitis

inflammation of the conjunctiva- (PINKEYE) -most common bacterial cause: Haemophilus influenza -viral conjunctivitus- usually caused by adenoviruses -contact lenses- accompanied by increased incidence of infections of the eye

Normal Microbiota of the Skin

• 1. Microorganisms that live on skin are resistant to desiccation and high concentrations of salt. • 2. Gram-positive cocci predominate on the skin. • 3. The normal skin microbiota are not completely removed by washing. • 4. Members of the genus Propionibacterium metabolize oil from the oil glands and colonize hair follicles. • 5. Malassezia furfur yeast grows on oily secretions and may be the cause of dandruff.

Microbial Diseases of the Eye

• 1. The mucous membrane lining the eyelid and covering the eyeball is the conjunctiva.

Structure and Function of the Skin

• 1. The outer portion of the skin (epidermis) contains keratin, a waterproof coating. • 2. The inner portion of the skin, the dermis, contains hair follicles, sweat ducts, and oil glands that provide passageways for microorganisms. • 3. Sebum and perspiration are secretions of the skin that can inhibit the growth of microorganisms. • 4. Sebum and perspiration provide nutrients for some microorganisms. • 5. Body cavities are lined with epithelial cells. When these cells secrete mucus, they constitute the mucous membrane.

SUMMARY! Introduction

• 1. The skin is a physical barrier against microorganisms. • 2. Moist areas of the skin support larger populations of bacteria than dry areas. • 3. Human skin produces antibiotics called defensins.

Microbial Diseases of the SKin

• 1. Vesicles are small fluid-filled lesions; bullae are vesicles larger than 1 cm; macules are flat, reddened lesions; papules are raised lesions; and pustules are raised lesions containing pus.

Inflammation of the Eye Membranes: Conjunctivitis

• 2. Conjunctivitis is caused by several bacteria and can be transmitted by improperly disinfected contact lenses.

Rubella

Etiologic Agent: -Togavirus Clinical Symptoms: -Macular rash Mode of transmission: Respiratory route

*Discuss the usual mode of entry of bacteria into the skin Compare bacterial skin infections with infections caused by fungi and viruses with respect to mode of entry

-Bacteria usually enter through inapparent openings in the skin -Fungal pathogens (except subcutaneous) often grow on the skin itself. -Viral infections of the skin (except warts and herpes simplex) most often gain access to the body through the respiratory tract.

Warts

Etiologic Agent: -Papovavirus Clinical Symptoms: -Benign tumor Mode of transmission: -Direct Contact

Streptococcal Skin INfections

-Gram-Positive, Spherical (BOTH) -grow in CHAINS -cause meningitis, pneumonia, sore throats, otitis media, dental caries -streptococci grow, secrete toxins and enzymes -hemolysin- lysis of RBC -alpha-hemolytic, beta-hemolytic, gamma-hemolytic -BETA-hemolytic; associated w/ human DISEASE (ie- GAS- group A streptococci-Streptococcus pyogenes) -M protein- prevents activation of complement & allows microbe to EVADE PHAGOCYTOSIS & KILLING BY NEUTROPHILS -helps bacteria ADHERE to and COLONIZE mucous membranes -the GAS produce substances that promote rapid spread of infection though tissue and by liquefying pus -among these are streptokinase (enzymes that dissolve blood clots), hyaluronidase (enzyme that dissolves the hyaluronic acid in conncective tissue where it serves to cement cells together), and deoxyri-bonucleases (enzyme that degrades DNA) -these streptococci also produce certain enzymes- streptolysins- lyse red blood cells and are toxic to neutrophils -serious when S. pyogenes infects dermal layer (erysipelas) - can enter bloodstream--> sepsis -infection- first appears on face and is preceded by streptococcal sore throat. -high fever -sensitive to beta-lactam-type antibiotics (esp cephalosporin) Example: Necrotizing Fascititis -caused by an invasive group A streptococcal infection- "flesh eating bacteria" -entered through minor breaks in the skin -once established, may destroy tissue as rapid as surgeons can remove it. -exotoxin produced by streptococcal M protein types, exotoxin A-acts as a superantigen, causing immune system to contribute to the damage. -Necrotizing Fascititis- often associated w/ streptococcal toxic shock syndrome -resembles staphylococcal TSS -rash- less likely to be present -bacteremia- more likely to occur -M proteins- shed from surface of these streptococci from a complex w/ fibrinogen that binds to neutrophils. -cause activation of neutrophils-release of damaging enzymes and consequent shock and organ damage.

*Are skin bacteria most likely to be gram-positive or gram-negative? Why?

-Gram-positive cocci predominate on the skin -they are resistant to desiccation (thicker peptidoglycan layer) and high concentrations of salt -Gram-pos cocci are resistant to env stresses such as drying and high osmotic pressures found in concentrated salt or sugar solutions

*Give 2 examples of normal microbiota of skin

-Staphylococcus epidermidis -Proprionibacterium acnes

Acne

Etiologic Agent: -Proprionibacterium acnes Clinical Symptoms: -Infected oil glands Mode of transmission: Direct Contact

*How does dermatitis develop? What is the cause and what are the symptoms? How is it treated?

-cause: Pseudomonas aeruginosa -opportunistic pathogen -Pseudomonas- cause of Pseudomonas dermatitis -Pseudomonas (aerobic, gram NEG, rods, in SOIL & H2O, can grow on unusual organic matter, resistant to antibiotics and disinfectants) -self-limiting rash (2 weeks duration) -associated w/ swimming pools , saunas, hot tubs -when ppl use these facilities, ALKALINITY RISES, chlorine becomes less effective -conc of nutrients that supports growth of pseudomonas INCREASES -hot water- cause hair follicles to open wider--> bacteria enters -swimmers ear- otitis externa- infection of external ear canal leading to eardrum that is caused by pseudomonas. -resistant to antibiotics -quinolones- newer, antipseudomonal beta-lactam antibiotics- drug of choice

*How does acne develop? What is one common cause of acne? How is acne treated?

-skin cells that are shed inside the hair follicles are able to leave normally, but acne develops when cells are shed in higher than normal numbers -they combine w/ sebum and the mixture clogs the follicle. -sebum accumulates- whiteheads (comedos) form -if blockage protrudes through skin, a blackhead (comedone) forms -dark color of blackheads- due to lipid oxidization and other causes -topical agents- do not affect sebum formation (root cause of acne)- depends on hormones such as estrogens or androgens -Diet has no known effect on sebum production -pregnancy- some hormone based contraceptive methods, and hormonal changes w/ age reduce sebum formation and influence acne Comedonal (mild) acne- usually treated w/ topical agents (azelaic acid (Azelex), salicylic acid, -topical agents do not affect sebum formation Inflammatory (moderate) acne- bacterial action -Propionibacterium acnes -nutritional requirement for glycerol in sebum -metabolizes sebum- forms free fatty acids that cause an inflammatory response -neutrophils are attracted to site- secrete enzymes that damage wall of hair follicle- inflammation- pustules and papules -can be treated w/antibiotics. -benzoyl peroxides are effective (clindamycin and erythromycin- combination of antibiotics and benzoyl peroxide) -can progress to nodular cystic (severe) acne -inflamed lesions filled w/ pus deep w/in the skin, leaving scars -Treatment: Isotretinoin- reduces formation of sebum -Accutane- now discontinued (can cause serious side effects

*Name a bacterial eye infection and a viral eye infection

Bacterial Eye Infection: Opthalmia Neonatorum -serious form of conjunctivitis -caused by Neisseria gonorrhoeae -large amounts of pus formed -if treatment is delayed- ulceration of cornea results -disease- acquired as infant passes through birth canal -infection- carries high risk of blindness -used to be treated w/ silver nitrate -now replaced w/ antibiotics - helps treat coinfections by gonococci and sexually transmitted chlamydias (silver nitrate not effective against chlamydias) Viral Eye Infection -Herpetic Keratitis -caused by herpes simplex type 1 virus that causes cold sores -latent in trigeminal nerves -disease is an infection of CORNEA- resulting in deep ulcers that may be most common cause of infectious blindness in US -Treatment: drug TRIFLURIDINE- effective.

Fever Blisters

Etiologic Agent: -Herpesvirus Clinical Symptoms: -Recurrent "blisters" Mode of transmission: -Direct COntact

Chickenpox

Etiologic Agent: -Herpesvirus Clinical Symptoms: -Vesicular rash Mode of transmission: -Respiratory Route

Measles

Etiologic Agent: -Paramyxovirus Clinical Symptoms: -Papular rash, Koplik's spots Mode of transmission: -Respiratory Route

*Define mycosis

Fungal infection of the body -skin- most susceptible to microbes that can resist high osmotic pressure and low moisture (fungi)

*Name 2 fungal infections of the skin

Ringworm (Tinea Capitis)- ringworm of the scalp- common among elementary school children, can result in bald patches -Tinea Cruris- ringworm of groin, jock itch -Tinea pedis-ringworm of feet, or ATHLETES FOOT

*What are the similarities and differences between Staphylococcus spp. and Streptococcus spp. Give an example of an infection caused by each Staphylococcus spp.

Staphylococcus spp. -spherical (BOTH) -gram-positive (BOTH) -irregular clusters -coagulase-negative- s, epidermidis (normal flora) -S. aureus- POSITIVE FOR COAGULASE Coagulase is a protein enzyme produced by several microorganisms that enables the conversion of fibrinogen to fibrin. In the laboratory, it is used to distinguish between different types of Staphylococcus isolates. -infects skin, stimulates inflammatory response, macrophages, and neutrophils are attracted to site of infection. -most strains secrete a protein that blocks chemotaxis of neutrophils to infection site. -if bacterium encounters phagocytic cells- it produces toxins that kills them -resistant to opsonization- failing this it can survive well within phagosome -Other PROTEINS it secretes- NEUTRALIZE the antimicrobial peptide DEFENSINS on the skin -cell wall is lysozyme resistant -sometimes responds to immune system as a SUPERANTIGEN, but is often able to evade adaptive immune system entirely -all humans have antibodies against S. aureus but they do not effectively prevent repeated infections -Antibiotic-resistant strains have emerged- difficult to treat -very common in nasal passages (transported from there to the skin) -enters body through openings in skin barrier (ie hair follicles) -Folliculitis- infection that occur as pimples -Sty- infected follicle of an eyelash -Furuncle (boil)- type fo abscess- more serious hair follicle infection- a localized region of puss surrounded by inflamed tissue -antibiotics- dont penetrate abscess ; need to drain puss -when body fails to wall off a furuncle (boil)--> neighboring tissue progressively invaded (carbuncle- a hard round deep inflammation of tissue under the skin).-- fever Example: -cause of IMPETIGO- highly contageous skin infection -children 2-5 yrs -transmission: Direct Contact - both S. aureus and S. pyogenes can be involved -2 forms of disease: nonbullous impetigo andbullousimpetigo -pathogen- enters through break in skin -symptoms- result from hosts response to infection -lesions- eventually rupture and form light-colored crusts -topical antibiotics Example 2 -skalded skin syndrome- characteristic of LATE stages of toxic shock syndrome (TSS) -fever, vomiting, sunburn-like rash -followed by shock, organ failure (esp kidneys) -when tampons are left in too long staphylococcal growth -staphylococcal toxin formed at growth site and circulates in bloodstream -symptoms are thought to be a result of the superantigenic properties of the toxin

*Describe 2 viral infections of the skin, listing the causative viruses in each case

Warts: -papillomavirus -benign skin growths -incubation period of several weeks before warts appear from time of infection -treatment- liquid nitrogen, dry them out w/ electrical current (electrodesiccation) or burn w/ acids -topical applications- pdofilox or imiquimod (aldara) (ladder stimulates production of antiviral interferons) Smallpox (Variola) -caused by orthopoxvirus; known as the smallpox (variola) virus -Variola major, Variola minor -Transmitted: Respiratory Route -virus infects many organs before moving into bloodstream, then infecting skin -growth of virus on skin cause lesions that become pustular after 10 days or so. Chickenpox (Varicella) and Shingles (Herpes Zoster) - initial infection: herpesvirus varicella-zoster (human herpesvirus 3) -Transmission: Respiratory route -Infection- localizes skin after 2 weeks -infectedskin is vesicular for 3-4 days- vesicles w/ pus, rupture, and form scab before healing -characteristic of herpes virus & w/ the varicella-zoster virus- can remain LATENT within body -after primary infection, virus enters peripheral nerves and moves to central nerve ganglion where it persists as viral DNA -humoral antibodies cant penetrate into nerve cells -because no viral antigens are expressed on the surface of the nerve cell, cytotoxic T cells are not activated. -neither arm of the specific immune system disturbs the latentvirus -Latent varicella-zoster virus- located in dorsal root ganglion near spine -virus may be reactivated decades later -trigger: stress, lower immune competence w/ aging -virions produced by reactivated DNA move along the peripheral nerve to the cutaneous sensory nerves of the skin, where they cause a new outbreak of the virus in the form of SHINGLES (herpes zoster) -usually distributed about the waist, upper chest or back -infection follows distribution of the affected cutaneous sensory nerves -burning, stinging, pain -different expression of virus that causes chickenpox -antiviral drugs: acyclovir, valacyclovir, famciclovir - treatment for shingles -for immunocompromised patients and patients w/ ocular involvement, treatment w/ antivirals is mandatory

Bacterial Diseases of the Skin

• 2. Staphylococci are gram-positive bacteria that often grow in clusters. • 3. The majority of skin microbiota consist of coagulase-negative Staphylococcus epidermidis. • 4. Almost all pathogenic strains of S. aureus produce coagulase. • 5. Pathogenic S. aureus can produce enterotoxins, leukocidins, and exfoliative toxin. • 6. Localized infections (sties, pimples, and carbuncles) result from S. aureus entering openings in the skin. • 7. Impetigo is a highly contagious superficial skin infection caused by S. aureus. • 8. Toxemia occurs when toxins enter the bloodstream; staphylococcal toxemias include scalded skin syndrome and toxic shock syndrome. • 9. Streptococci are gram-positive cocci that often grow in chains. • 10. Streptococci are classified according to their hemolytic enzymes and cell wall antigens. • 11. Group A beta-hemolytic streptococci (including Streptococcus pyogenes) are the pathogens most important to humans. • 12. Group A beta-hemolytic streptococci produce a number of virulence factors: M protein, deoxyribonuclease, streptokinases, and hyaluronidase. • 13. Erysipelas is caused by S. pyogenes. • 14. Invasive group A beta-hemolytic streptococci cause severe and rapid tissue destruction. • 15. Pseudomonads are gram-negative rods. They are aerobes found primarily in soil and water that are resistant to many disinfectants and antibiotics. • 16. Pseudomonas aeruginosa produces an endotoxin and several exotoxins. • 17. Diseases caused by P. aeruginosa include otitis externa, respiratory infections, burn infections, and dermatitis. • 18. Infections have a characteristic blue-green pus caused by the pigment pyocyanin. • 19. Quinolones are useful in treating P. aeruginosa infections. • 20. Mycobacterium ulcerans causes deep-tissue ulceration. • 21. Propionibacterium acnes can metabolize sebum trapped in hair follicles. • 22. Metabolic end-products (fatty acids) cause inflammatory acne. • 23. Tretinoin, benzoyl peroxide, erythromycin, and light therapy are used to treat acne.

Viral Diseases of the Skin

• 24. Papillomaviruses cause skin cells to proliferate and produce a benign growth called a wart or papilloma. • 25. Warts are spread by direct contact. • 26. Warts may regress spontaneously or be removed chemically or physically. • 27. Variola virus causes two types of skin infections: variola major and variola minor. • 28. Smallpox is transmitted by the respiratory route, and the virus is moved to the skin via the bloodstream. • 29. The only host for smallpox is humans. • 30. Smallpox has been eradicated as a result of a vaccination effort by the World Health Organization. • 31. Varicella-zoster virus is transmitted by the respiratory route and is localized in skin cells, causing a vesicular rash. • 32. Complications of chickenpox include encephalitis and Reye's syndrome. • 33. After chickenpox, the virus can remain latent in nerve cells and subsequently activate as shingles. • 34. Shingles is characterized by a vesicular rash along the affected cutaneous sensory nerves. • 35. The virus can be treated with acyclovir. An attenuated live vaccine is available. • 36. Herpes simplex infection of mucosal cells results in cold sores and occasionally encephalitis. • 37. The virus remains latent in nerve cells, and cold sores can recur when the virus is activated. • 38. HSV-1 is transmitted primarily by oral and respiratory routes. • 39. Herpes encephalitis occurs when herpes simplex viruses infect the brain. • 40. Acyclovir has proven successful in treating herpes encephalitis. • 41. Measles is caused by measles virus and is transmitted by the respiratory route. • 42. Vaccination provides effective long-term immunity. • 43. After the virus has incubated in the upper respiratory tract, macular lesions appear on the skin, and Koplik's spots appear on the oral mucosa. • 44. Complications of measles include middle ear infections, pneumonia, encephalitis, and secondary bacterial infections. • 45. The rubella virus is transmitted by the respiratory route. • 46. An infected individual might experience a red rash and light fever or be asymptomatic. • 47. Congenital rubella syndrome can affect a fetus when a woman contracts rubella during the first trimester of her pregnancy. • 48. Damage from congenital rubella syndrome includes stillbirth, deafness, eye cataracts, heart defects, and mental retardation. • 49. Vaccination with live rubella virus provides immunity of unknown duration. • 50. Human parvovirus B19 causes fifth disease, and HHV-6 causes roseola.

Bacterial Diseases of the Eye

• 3. Bacterial microbiota of the eye usually originate from the skin and upper respiratory tract. • 4. Ophthalmia neonatorum is caused by the transmission of Neisseria gonorrhoeae from an infected mother to an infant during its passage through the birth canal. • 5. All newborn infants are treated with an antibiotic to prevent Neisseria and Chlamydia infection. • 6. Inclusion conjunctivitis is an infection of the conjunctiva caused by Chlamydia trachomatis. It is transmitted to infants during birth and is transmitted in unchlorinated swimming water. • 7. In trachoma, which is caused by C. trachomatis, scar tissue forms on the cornea. • 8. Trachoma is transmitted by hands, fomites, and perhaps flies.

Fungal Diseases of the Skin and Nails

• 51. Fungi that colonize the outer layer of the epidermis cause dermatomycoses. • 52. Microsporum, Trichophyton, and Epidermophyton cause dermatomycoses called ringworm, or tinea. • 53. These fungi grow on keratin-containing epidermis, such as hair, skin, and nails. • 54. Ringworm and athlete's foot are usually treated with topical antifungal chemicals. • 55. Diagnosis is based on the microscopic examination of skin scrapings or fungal culture. • 56. Sporotrichosis results from a soil fungus that penetrates the skin through a wound. • 57. The fungi grow and produce subcutaneous nodules along the lymphatic vessels. • 58. Candida albicans causes infections of mucous membranes and is a common cause of thrush (in oral mucosa) and vaginitis. • 59. C. albicans is an opportunistic pathogen that may proliferate when the normal bacterial microbiota are suppressed. • 60. Topical antifungal chemicals may be used to treat candidiasis.

Parasitic Infestation of the Skin

• 61. Scabies is caused by a mite burrowing and laying eggs in the skin. • 62. Pediculosis is an infestation by Pediculus humanus.

Other Infectious Diseases of the Eye

• 9. Fusarium and Aspergillus fungi can infect the eye. • 10. Herpetic keratitis causes corneal ulcers. The etiology is HSV-1 that invades the central nervous system and can recur. • 11. Acanthamoeba protozoa, transmitted via water, can cause a serious form of keratitis.