1. Microbial Diseases of the Skin and Eyes
Chapter 21
Microbial Diseases of the Skin and Eyes

2. Structure and Function of the Skin
Skin = epidermis (keratin) + dermis
First line of defense (physical and chemical barrier)
Unbroken epidermis is an effective physical barrier
hair follicles, sweat gland ducts, and oil gland ducts provide passageways for microbes to enter the skin and penetrate deeper tissues
Perspiration provides moisture and some nutrients for microbial growth; sebum provides some nutrients

3. Skin
Perspiration contains salt and antimicrobial peptide to inhibit microbes
Lysozyme hydrolyzes peptidoglycan
Fatty acids (from sebum) inhibit some pathogen
Figure 21.1

4. Mucous Membranes Line body cavities
Epithelial cells attached to an extracellular matrix (basement membrane)
Cells secrete mucus
Some have cilia
Often acidic; limit microbial population
Lysozyme in tears destroys the cell wall

5. Normal Microbiota of the Skin
Resistant to drying & tolerant to high salt
Gram-positive, salt-tolerant bacteria
Staphylococci
Micrococci
Diphtheroids
Vigorous washing can reduce numbers, but will not eliminate them
Figure 14.1a

6. Microbial Diseases of the Skin
Figure 21.2

7. Microbial Diseases of the Skin
Exanthem
Skin rash arising from another focus of infection
Enanthem
Mucous membrane rash arising from another focus of infection
Bacterial Disease of the Skin
Staphylococcus & Streptococcus are frequent causes of skin-related diseases

8. Staphylococcal Skin Infections
Staphylococci: gram-positive cocci in clusters
S. epidermidis
Gram-positive cocci, coagulase-negative
very common on the skin (90% of the normal microbiota); opportunistic pathogen
Staphylococcus aureus
Gram-positive cocci, pathogenic S. aureus are coagulase-positive
Leukocidin (destroy phagocytic leukocytes)
Exfoliative toxin (cause scalded skin syndrome)

9. Staphylococcal Skin Infections
Enterotoxin (cause Staphylococcal food poisoning)
S. aureus in hospital environment quickly becomes resistant to antibiotics (MRSA) and vancomycin-resistant S. aureus
Many S. aureus produce penicillinase
Folliculitis
Infections of hair follicles
Sty
Folliculitis of an eyelash

10. Staphylococcal Skin Infections
Furuncle
Abscess; pus surrounded by inflamed tissue
Carbuncle
Inflammation of tissue under the skin
Impetigo of the newborn
Toxemia
Scalded skin syndrome
Toxic shock syndrome (TSS)
Figure 21.4

11. Streptococcal Skin Infections
Gram-positive cocci in chains
Secrete toxins and enzymes
Hemolysins (toxin): lyse red blood cells
Alpha-, beta-, gamma-hemolytic streptococci
Beta-hemolytic streptococci often associated with human disease
Further subdivided into different serological groups (A through T)
Group A beta-hemolytic streptococci most important

12. Streptococcal Skin Infections
Streptococcus pyogenes = group A beta-hemolytic streptococci
M proteins
Antiphagocytic
Aid adherence for colonization of mucous membrane
Figure 21.5

13. Streptococcal Skin Infections
Generally localized
Can be highly destructive; produce substances that promote the rapid spread of infection
Streptokinases (dissolve blood clots)
Hyaluronidase (dissolves hyaluronic acid that cement connective tissue)
Deoxyribonucleases (degrade DNA)
Erythrogenic toxins (cause red rash & other symptoms of scarlet fever)

14. Streptococcal Skin Infections
Infects dermal layer of the skin
Erysipelas
Can progress to local tissue destruction
Impetigo
Isolated pustules that become crusted
Toddlers and children of grade-school age
Figure 21.6, 7

15. Invasive Group A Streptococcal Infections (“Flesh-eating bacteria”)
Destroy tissue rapidly; mortality rates over 40%
Streptokinases
Hyaluronidase
Exotoxin A (superantigen)
Cellulitis
Myositis
Necrotizing fasciitis
Figure 21.8

16. Infections by Pseudomonads
Pseudomonas aeruginosa
Gram-negative, aerobic rod
Opportunistic pathogen; cause of many nosocomial infections
Can grow on traces of unusual organic matter, soap films or cap liner adhesives; often grow in dense biofilms
Resistant to many antibiotics and disinfectants
Produce several exotoxins; also has endotoxin

17. Infections by Pseudomonads
Pseudomonas dermatitis (swimming pool, hot tubs)
Otitis externa (swimmer’s ear)
Opportunistic pathogen
Cystic fibrosis patients
Post-burn infections pyocyanin produces a blue-green pus in burn patients

18. Acne Inflammatory acne Most common skin disease
Caused by blockage of channels for the passage of sebum to the skin surface
Three categories: comedonal acne, inflammatory acne, & nodular cystic acne
Comedonal acne
Occurs when sebum channels are blocked with shed cells
Usually treated with topical agents that do not affect sebum formation
Inflammatory acne
Due to Propionibacterium acnes (Gram-positive, anaerobic rod)

19. Acne Nodular cystic acne
Bacteria has a nutritional requirement for glycerol in sebum inflammation caused by free fatty acids formed from metabolizing the sebum formation of pustules and papules
Treatment:
Preventing sebum formation (isotretinoin teratogenic)
Antibiotics
Benzoyl peroxide to loosen clogged follicles
Clear light system visible (blue) light (kills P. acnes)
Nodular cystic acne
Formation of nodules or cysts = inflamed lesions filled with pus deep within the skin leave prominent scars
Treatment: isotretinoin

20. Viral Diseases of the Skin: Warts
Benign skin growths caused by viruses
Papillomaviruses different kinds of warts
Do not form cancer; but papillomaviruses are associated with some skin & cervical cancer
Transmitted through direct contact
Treatment:
Cryotherapy: apply extremely cold liquid nitrogen

21. Warts Electrodesiccation: dry them with an electrical current
Burn them with acids
Topical application of prescription drugs
Imiquimod (stimulate interferon production)
Interferon (injection)
Lasers (risk of aerosol transmission)

22. Smallpox (Variola) Smallpox virus (Orthopox virus)
Variola major has 20% mortality rate
Variola minor has <1% mortality rate
Transmission by respiratory route
Eradicated due to successful vaccination & there are no animal host reservoirs for the disease
Bioterrorism vaccination only for military and healthcare workers

23. Smallpox (Variola) Monkeypox outbreak (started in zoo monkeys)
Known to jump from animals to humans; human-to-human transmission is very limited
Seen some cases the USA recently
Disease closely resembles smallpox in symptoms and mortality rate
Prevention by smallpox vaccination

24. Chickenpox (Varicella) and shingles (Herpes Zoster)
Chickenpox relatively mild in children; tends to be more serious in adults
Results of initial infection with herpesvirus varicella-zoster (human herpesvirus 3)
Transmitted via respiratory route & infection localized in skin cells
Ability to remain latent within body cause shingles (a new outbreak of virus)

25. Chickenpox Causes pus-filled vesicles
Virus may remain latent in dorsal root ganglia near the spine following a primary infection
persists as viral DNA
Escapes immune response (Ab cannot penetrate into the nerve cells & no surface viral Ags expressed)
Figure 21.10a

26. Shingles
Reactivation of latent HHV-3 releases viruses that move along peripheral nerves to skin.
Triggered by stress, or lower immune competence due to aging
Occur in distinctive areas (typically around waist); usually limited to one side of the body at a time
Figure 21.10b

27. Herpes simplex virus (HSV)
HSV-1 (Human herpes virus 1, HHV-1) and HSV-2 (HHV-2)
HHV-1 transmitted by oral or respiratory routes
Usually infected in infancy (subclinical infection)
Cold sores or fever blisters (vesicles near the outer red margin of the lips)
Remain latent in the trigeminal nerve ganglia
Recurrence due to excessive exposure to UV radiation, emotional upsets, or hormonal changes

28. Herpes simplex
Herpes gladiatorum (vesicles on skin) via skin contact among wrestlers
Herpes whitlow (vesicles on fingers) among healthcare workers
HHV-2 transmitted sexually (genital herpes)
Can remain latent in sacral nerve ganglia
Herpes encephalitis, rare, but can be caused by both viruses HHV-2 has up to a 70% fatality rate
Acyclovir may lessen symptoms

29. Measles (Rubeola) Measles virus; humans are the only reservoir
Transmitted by respiratory route; extremely contagious
Infectious before symptoms appear
Macular rash and Koplik's spots (lesions of oral cavity; diagnostic indicator)
Prevented by vaccination
Complications of measles:
Encephalitis in 1 in 1000 cases
Subacute sclerosing panencephalitis in 1/1,000,000

30. Measles (Rubeola)
Figure 21.13

31. Rubella (German Measles)
Rubella virus
Transmitted via respiratory route
Macular rash and fever
Milder viral disease than rubeola (measles)
Complications are rare (encephalitic in about 1/6,000, mainly in adults)
Congenital rubella syndrome causes severe fetal damage during first trimester
Prevented by vaccination

32. Other viral rashes Fifth disease Roseola
A 1905 list of skin rashes included #1-measles, #2-scarlet fever, #3-rubella, #4-Filatow-Dukes (mild scarlet fever), and #5-Fifth Disease
Human parvovirus B19 produces mild flu-like symptoms with facial rash (“slapped-cheek”)
Roseola
Human herpesvirus 6 causes a high fever and rash, lasting for 1-2 days
Mild childhood disease

33. Fungal Diseases of the Skin and Nails
Mycoses: any fungal infection of the body
Cutaneous mycoses: fungal infection of the epidermis, nails, or hair
Dermatophytes: fungi that colonize the hair, nails, and the outer layer of the epidermis
Metabolize keratin
Trichophyton: infects hair, skin, nails
Epidermophyton: infects skin and nails
Microsporum: infects hair and skin

34. Cutaneous mycoses Dermatomycoses (tineas or ringworm) Treatment
Tinea capitis: ringworm of the scalp bald patches
Tinea curis: ringworm of the groin, or jock itch
Tinea pedis: ringworm of the feet, or athlete’s foot
Tinea unguium (onychomycosis): nail infection
Treatment
Oral griseofulvin (for hair infection)
Topical miconazole

35. Subcutaneous mycoses
Subcutaneous mycoses: fungal infection of tissue beneath the skin
Usually caused by fungi that inhabit the soil
Sporotrichosis
Sporothrix schenckii enters puncture wound form small ulcers on the hands
Occurs among gardeners or others who work with soil
Treated with ingestion of a dilute solution of potassium iodide (KI)

36. Candidiasis Candida albicans (yeast)
Candidiasis may result from suppression of competing bacteria by antibiotics
Occurs in skin; mucous membranes of genitourinary tract and mouth
Thrush is an infection of mucous membranes of mouth
If infection becomes systemic fulminating disease leading to death
Topical treatment with miconazole or nystatin

37. Candidiasis
Figure 21.17

38. Parasitic infections of the Skin: Scabies
Tiny mite Sarcoptes scabiei burrows in the skin to lay eggs
Figure 21.18

39. Scabies Intense local itching
May appear as a variety of inflammatory skin lesions (due to secondary infections from scratching)
Transmitted via intimate contact (sexually, too)
Treatment with topical insecticides

40. Pediculosis (lice) Pediculosis: infestations by lice
Pediculus humanus capitis (head louse)
P. h. corporis (body louse) can spread diseases (epidemic typhus)
Feed on blood
Itching due to sensitization to louse saliva
Scratching can lead to secondary infections
Lay eggs (nits) on hair

41. Pediculosis (lice)
Head louse has especially adapted legs to grasp scalp hairs
Treatment with topical insecticides
Combing out the nits with fine-toothed louse combs
Figure 21.19

42. Microbial Diseases of the Eye
Conjunctivitis (pinkeye): inflammation of the conjunctiva
Haemophilus influenzae & adenoviruses
Various microbes (bacteria, viruses, and protozoa)
Associated with unsanitary contact lenses
Neonatal gonorrheal ophthalmia
Neisseria gonorrhoeae
Transmitted to newborn's eyes during passage through the birth canal

43. Bacterial Diseases of the Eye
Prevented by treatment newborn's eyes with antibiotics (silver nitrate in old days)
Chlamydia trachomatis
Inclusion conjunctivitis
Transmitted to newborn's eyes during passage through the birth canal
Spread through swimming pool water
Treated with tetracycline ointment

44. Bacterial Diseases of the Eye
Trachoma
Greatest cause of blindness worldwide
Infection causes permanent scarring; scars abrade the cornea leading to blindness
Transmitted by hand contact or by sharing personal objects (e.g. towels)
Treated with tetracycline ointments; control through sanitary practices and health education

45. Other Infectious Diseases of the Eye
Keratitis: inflammation of the cornea
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
Severe damage may require a corneal transplant

46. Microbial Diseases of the Eye
Figure 21.21

47. Chapter Review
1. Review the structure and function of skin as the first line of defense
Skin = epidermis (keratin) + dermis
Unbroken epidermis is an effective physical barrier
hair follicles, sweat gland ducts, and oil gland ducts provide passageways for microbes to enter the skin and penetrate deeper tissues
Perspiration provides moisture and some nutrients for microbial growth; sebum provides some nutrients

48. Chapter Review Mucous membranes
Perspiration contains salt and antimicrobial peptide to inhibit microbes
Lysozyme hydrolyzes peptidoglycan
Fatty acids (from sebum) inhibit some pathogen
Mucous membranes
Line body cavities
Epithelial cells attached to an extracellular matrix (basement membrane)
Cells secrete mucus
Some have cilia

49. Chapter Review Normal microbiota of the skin
Often acidic; limit microbial population
Lysozyme in tears destroys the cell wall
Normal microbiota of the skin
Resistant to drying & tolerant to high salt
Gram-positive, salt-tolerant bacteria (e.g. Staphylococci, Micrococci, Diphtheroids)
Vigorous washing can reduce numbers, but will not eliminate them recolonize the skin

50. Chapter Review
2. Know the characteristics of bacterial pathogens that cause skin diseases & the infections they cause
Staphylococcus & Streptococcus are frequent causes skin-related diseases
Pseudomonads are opportunistic pathogens
Staphylococcal skin infections
Staphylococci: Gram-positive cocci in clusters
Staphylococcus epidermidis (S. epidermidis) are coagulase-negative; 90% of the normal microbiota of the skin; opportunistic pathogen

51. Chapter Review Pathogenic S. aureus are coagulase-positive
Produce leukocidin (destroy phagocytic leukocytes); exfoliative toxin (cause scalded skin syndrome); & enterotoxin (cause Staphylococcal food poisoning)
Become antibiotic resistant quickly in hospital environment
Diseases caused by S. aureus
Folliculitis: infections of hair follicles
Sty: folliculitis of an eyelash
Carbuncle : inflammation of the tissue under the skin
Impetigo of the newborn
Toxemia

52. Chapter Review Streptococcal skin infections
Scalded skin syndrome
Toxic shock syndrome
Streptococcal skin infections
Streptococcus: gram-positive cocci in chains; classified into three groups based on their hemolytic ability
Alpha-hemolytic: partial hemolysis of red blood cells (RBCs)
Beta-hemolytic: complete hemolysis of RBCs
Gamma-hemolytic: no hemolysis of RBCs
Beta-hemolytic streptococci often associated with human disease; Group A most important

53. Chapter Review
Group A beta-hemolytic streptococci = Streptococcus pyogenes (S. pyogenes)
S. pyogenes’ pathogenicity due to
M proteins (adherence & antiphagocytic)
Streptokinases: dissolve blood clots
Hyaluronidase: dissolve hyaluronic acid
Deoxyribonucleases: degrade DNA
Erythrogenic toxins: cause red rash & other symptoms of scarlet fever
Diseases caused by S. pyogenes
Erysipelas
Impetigo

54. Chapter Review Invasive Group A Streptococcal infections
Especially pathogenic; “flesh-eating bacteria”
Destroy tissue rapidly; mortality rates over 40%
Produce streptokinases, hyaluronidase, exotoxin A (major contributing factor by causing immune system to cause damage to the infected host)
Diseases caused by invasive group A strep.
Cellulitis
Myositis
Necrotizing fasciitis

55. Chapter Review
3. Know the viruses that cause skin diseases & the infections they cause
Warts
Papillomaviruses do not form cancer, but are associated with some skin & cervical cancer
Chickenpox and Shingles
Results from initial infection with herpresvirus varicella-zoster (human herpesvirus 3)
Ability to remain latent in body, when reactivated later in life (a new outbreak of virus) cause shingles

56. Chapter Review Herpes simplex virus (HSV)
Reactivation is triggered by stress, or lower immune competence due to aging
Herpes simplex virus (HSV)
HSV-1 (human herpes virus-1, HHV-1) cause cold sores or fever blisters (usually infected in infancy); herpes gladiatorum among wrestlers; herpes whitlow among healthcare workers
Remain latent and reactivated due to excessive exposure to UV radiation, emotional upsets, or hormonal changes

57. Chapter Review Measles HSV-2 (HHV-2) cause genital herpes
Can remain latent
Both HHV-1 and HHV-2 can cause herpes encephalitic (rare) HHV-2 infection more fatal (70% fatality rate)
Measles
Measles virus (Rubeola) extremely contagious (infectious before symptoms appear)
Prevented by vaccination

58. Chapter Review German measles (Rubella)
Rubella virus; milder viral disease than measles
Prevented by vaccination
4. Know some fungal diseases of the skin and nails
Cutaneous mycoses: fungal infection of the epidermis, nails, or hair
Caused by dermatophytes (fungi that colonize the hair, nails, and the outer layer of the epidermis); metabolize keratin

59. Chapter Review
Trichophyton: infects hair, skin, nails
Epidermophyton: infects skin and nails
Microsporum: infects hair and skin
Dermatomycoses (tineas or ringworm)
Tinea capitis: ringworm of the scalp bald patches
Tinea curis: ringworm of the groin, or jock itch
Tinea pedis: ringworm of the feet, or athlete’s foot
Tinea unguium (onychomycosis): nail infection
Subcutaneous mycoses: fungal infection of tissue beneath the skin
Usually caused by fungi that inhabit the soil

60. Chapter Review Sporotrichosis Candidiasis
Sporothrix schenckii enters puncture wound form small ulcers on the hands
Occurs among gardeners or others who work with soil
Candidiasis
Candida albicans (yeast)
Candidiasis may result from suppression of competing bacteria by antibiotics
Occurs in skin; mucous membranes of genitourinary tract and mouth

61. Chapter Review
Thrush is an infection of mucous membranes of mouth
If infection becomes systemic fulminating disease leading to death
5. Know the infectious diseases of the eye and the pathogens that cause them
Conjunctivitis (pinkeye): inflammation of the conjunctiva
Caused by various microbes (bacteria, viruses, and protozoa)
Haemophilus influenzae & adenoviruses most common cause

62. Chapter Review Inclusion conjunctivitis Trachoma
Caused by Chlamydia trachomatis
Transmitted to newborn’s eyes during passage through the birth canal
Spread through swimming pool water
Trachoma
Also caused by Chlamydia trachomatis
Greatest cause of blindness worldwide; cause permanent scarring; scars abrade the cornea leading to blindness

63. Chapter Review Keratitis: inflammation of the cornea
Herpetic keratitis
Caused by herpes simplex virus 1 (HHV-1)
Infects cornea, may cause blindness
Acanthamoeba keratitis
Caused by Acanthamoeba (protozoa) present in water
Severe damage may require a corneal transplant