1. Structure and Function of the Skin
Learning Objective
21-1 Describe the structure of the skin and mucous membranes and the ways pathogens can invade the skin.

2. The Structure of Human Skin
Perspiration and sebum contain nutrients
Salt inhibits microbes
Lysozyme hydrolyzes peptidoglycan
Fatty acids inhibit some pathogens
Figure 21.1

3. Mucous Membranes Line body cavities
The epithelial cells are attached to an extracellular matrix
Cells secrete mucus
Often acidic
Some cells have cilia
In eyes, washed by tears with lysozyme

4. Normal Microbiota of the Skin
Gram-positive, salt-tolerant bacteria
Staphylococci
Micrococci
Diphtheroids
Figure 14.1a

5. Normal Microbiota of the Skin
Grow on oils
Aerobes on surface
Corynebacterium xerosis
Anaerobes in hair follicles
Propionibacterium acnes
Yeast
Malassezia furfur

6. Skin Lesions
Figure 21.2

7. Bacterial Skin Diseases

8. Staphylococcal Skin Infections
Staphylococcus epidermidis
Gram-positive cocci, coagulase-negative
Staphylococcus aureus
Gram-positive cocci, coagulase-positive
Clinical Focus, p. 593

9. Staphylococcus aureus
Antibiotic resistant
Leukocidin
Resists opsonization
Survives in phagolysosome
Lysozyme resistant
Exfoliative toxin
Superantigen
Clinical Focus, p. 593

10. MRSA
Methicillin-resistant Staphylococcus Aureus (MRSA) is a type of staph bacteria that is resistant to certain antibiotics called beta-lactams.
These antibiotics include methicillin and other more common antibiotics such as oxacillin, penicillin, and amoxicillin.
In the community, most MRSA infections are skin infections.
More severe or potentially life-threatening MRSA infections occur most frequently among patients in healthcare settings.
While 25% to 30% of people are colonized* in the nose with staph, less than 2% are colonized with MRSA

11. Staphylococcal Skin Infections
Folliculitis: Infections of the hair follicles
Sty: Folliculitis of an eyelash
Furuncle: Abscess; pus surrounded by inflamed tissue
Carbuncle: Inflammation of tissue under the skin
Impetigo: crusting (nonbullous) sores, spread by autoinoculation

12. Nonbullous Lesions of Impetigo
Figure 21.4

13. Scalded Skin Syndrome Toxic shock syndrome (TSS)
Toxic shock syndrome toxin 1
Scalded skin syndrome (Staph spp.)
Bullous impetigo
Impetigo of the newborn
Epidermolytic endotoxin

14. Lesions of Skin Syndrome
Figure 21.5

15. Streptococcal Skin Infections
Streptococcus pyogenes
Group A beta-hemolytic streptococci
Hemolysins
Hyaluronidase
Stretolysins
M proteins

16. Streptococcal Skin Infections
Necrotizing fasciitis – “flesh-eating diesease”
Common in immune compromised
Group A streptococcus
Staphloccoccus aureus
C. perfrinogens
Bacteroides fragilis

17. Infections by Pseudomonads
Pseudomonas aeruginosa
Gram-negative, aerobic rod
Pseudomonas dermatitis
Otitis externa, or “swimmer’s ear”
Post-burn infections
Opportunistic

18. Cutaneous Anthrax
Most common and least dangerous infection caused by Bacillus anthracis
Forms a black eschar when endospores enter the skin and germinate there
11 cases occurred following bioterrorist attacks in the fall of 2001
20% mortality rate if untreated
CDC

19. Buruli Ulcer Caused by Mycobacterium ulcerans Deep, damaging ulcers
Exceeds incidence of leprosy

20. Classifications of Acne
Comedonal (mild) acne
Inflammatory (moderate) acne
Nodular cystic (severe) acne

21. Comedonal Acne Mild Treatment Sebum channels blocked with shed cells
Topical agents
Salicyclic acid preparations
Retinoids
Adapalene

22. Inflammatory Acne Propionibacterium acnes Gram-positive, anaerobic rod
Treatment
Preventing sebum formation (isotretinoin)
Benzoyl peroxide to loosen clogged follicles
Visible (blue) light (kills P. acnes)
Antibiotics

23. Nodular Cystic Acne
Severe
Treatment
Isotretinoin
Figure 21.9

24. Warts Papillomaviruses Treatment Removal
Cryotherapy
Electrodesiccation
Salicylic acid
Imiquimod (stimulates interferon production)
Bleomycin

25. Poxviruses Smallpox (variola) Monkeypox
Smallpox virus (orthopox virus)
Variola major has 20% mortality
Variola minor has <1% mortality
Eradicated by vaccination
Monkeypox
Prevention by smallpox vaccination

26. Smallpox Lesions
Figure 21.10

27. Chickenpox Varicella-zoster virus (human herpesvirus 3)
Transmitted by the respiratory route
Causes pus-filled vesicles
Virus may remain latent in dorsal root ganglia
Prevention: Live attenuated vaccine
Breakthrough varicella in vaccinated people

28. Figure 21.11a

29. Chicken Pox

30. Shingles
Reactivation of latent HHV-3 releases viruses that move along peripheral nerves to skin
Postherpetic neuralgia
Prevention: Live attenuated vaccine
Acyclovir may lessen symptoms

31. Figure 21.11b

32. Why is there an emergence of shingles among healthy populations?

33. Hand, Foot, and Mouth Disease (HFMD)
Most common in babies and children under age 5
Fever, sore throat, malaise
Painful spots inside the mouth
Red or blister-like spots on palms of hands and soles of feet and often genitals, buttocks, knees, and elbows
Caused by viruses in Enterovirus group
Cocksackie virus
© Dr. P. Marazzi/Science Source

34. Vesicular/Pustular Rash Diseases
Chickenpox
Smallpox
Hand, Foot, and Mouth Disease
Causative Organism(s)
Human herpesvirus 3 (varicella-zoster virus)
Variola virus
Enteroviruses, usually Coxsackie
Common Modes of Transmission
Droplet contact, inhalation of aerosolized lesion fluid
Droplet contact, indirect contact
Direct and droplet contact
Virulence Factors
Ability to fuse cells, ability to remain latent in ganglia
Ability to dampen, avoid immune response
N/A
Culture/Diagnosis
Based largely on clinical
appearance
Usually based on clinical
presentation and history
Prevention
Live attenuated vaccine; there is also vaccine to prevent reactivation of latent virus (shingles)
Live virus vaccine (vaccinia virus)
Hand hygiene
Treatment
None in uncomplicated cases; acyclovir for high risk
Cidofovir, immune globulin
None
Distinguishing Features
No fever prodrome; lesions are superficial; in centripetal
distribution (more in center of body)
Fever precedes rash, lesions are deep and in centrifugal distribution (more on extremities)
Fever prodrome, lesions in mouth first
Epidemiological Features
Chickenpox: vaccine decreased
hospital visits by 88%, ambulatory visits by 59%;
shingles: 1 million cases annually
Last natural case worldwide was in 1977
Category A Bioterrorism
Agent
Sporadic in most of world; unusual outbreaks in East and Southeast Asia since 1997 caused by an enterovirus

35. Herpes Simplex Human herpesvirus 1 (HSV-1) and 2 (HSV-2)
Cold sores or fever blisters (vesicles on lips)
Herpes gladiatorum (vesicles on skin)
Herpetic whitlow (vesicles on fingers)
Herpes encephalitis
HSV-1 can remain latent in trigeminal nerve ganglia

36. Cold Sores Caused by Herpes Simplex Virus
Figure 21.12

37. HSV-1 in the Trigeminal Nerve Ganglion
Figure 21.13

38. Herpes Simplex HSV-2 can remain latent in sacral nerve ganglia
HSV-2 encephalitis: 70% fatality
Encephalitis treatment: Acyclovir

39. Measles (Rubeola) Measles virus Transmitted by respiratory route
Macular rash and Koplik's spots
Prevented by vaccination
Figure 21.14

40. Sequelae of Measles
Small number of cases develop laryngitis, bronchopneumonia, and bacterial secondary infections
In 6% of the cases, the virus can cause pneumonia
Most serious complication is subacute sclerosing panencephalitis: progressive neurological degeneration of the cerebral cortex, white matter, and brain stem

41. Reported U.S. Cases of Measles, 1960–2007
Clinical Focus, p. 505

42. Rubella (German Measles)
Rubella virus
Macular rash and fever
Congenital rubella syndrome causes severe fetal damage
Prevented by vaccination
Figure 21.15

43. © James Stevenson/Science Source
Congenital Rubella
Infection in the first trimester
Induces miscarriage
Causes multiple permanent defects in the newborn
Congenital defects caused by rubella:
Deafness
Cardiac abnormalities
Ocular lesions
Mental and physical retardation
© James Stevenson/Science Source

44. Fifth Disease
Name derived from a 1905 list of skin rashes, which included
1. Measles
2. Scarlet fever
3. Rubella
4. Filatov Dukes disease (mild scarlet fever), and
5. Fifth disease, or erythema infectiosum
Human parvovirus B19 produces mild flu-like symptoms and facial rash

45. Roseola Caused by human herpesvirus 6 (HHV-6) and 7 (HHV-7)
High fever and rash lasting for 1–2 days

46. Disease
Measles (Rubeola)
Rubella
Causative organism(s)
Measles virus
Rubella virus
Common Modes of Transmission
Droplet contact
Virulence Factors
Syncytium formation, ability to suppress CMI
Inhibition of mitosis, induction
of apoptosis, and damage to
vascular endothelium
Culture/ Diagnosis
ELISA for IgM, acute/convalescent IgG; genotyping the virus during outbreaks
Acute IgM, acute/convalescent IgG
Prevention
Live attenuated vaccine
(MMR or MMRV)
Live attenuated vaccine (MMR
or MMRV)
Treatment
No antivirals; vitamin A, antibiotics for secondary bacterial infections
N/A
Distinguishing Features
Starts on head, spreads to whole
body, lasts over a week
Milder red rash, lasts
approximately 3 days
Epidemiological Features
Incidence increasing in North America; in developing countries incidence is 30 million cases/yr and 1 million deaths
Three cases reported in the United States in 2009; worldwide: 100,000 infants/yr born with congenital rubella syndrome

47. Disease
Fifth Disease
Roseola
Causative Organism(s)
Parvovirus B19
Human herpesvirus 6
Common Modes of Transmission
Droplet contact, direct contact
Unknown
Virulence Factors
N/A
Ability to remain latent
Culture/Diagnosis
Usually diagnosed clinically
Prevention
Treatment
Distinguishing Features
“Slapped-face” rash first, spreads to limbs and trunk, tends to be confluent rather than distinct bumps
High fever precedes rash stage;
rash not always present
Epidemiological Features
60% of population seropositive by age 20
>90% of population seropositive; 90% of disease cases occur before age of 2

48. Cutaneous Mycoses Dermatomycoses Also known as tineas or ringworm
Metabolize keratin

49. Dermatomycoses
Figure 21.16

50. Cutaneous Mycoses Tinea unguium – Fungal nail infection Treatment
Itraconazole
Terbinafine

51. Signs and Symptoms of Cutaneous Mycoses

52. Candidiasis Candida albicans (yeast)
Candidiasis may result from suppression of competing bacteria by antibiotics
Occurs in skin and mucous membranes of genitourinary tract and mouth
Thrush: An infection of mucous membranes of mouth
Topical treatment with miconazole or nystatin

53. Candida albicans
Figure 21.17a

54. Case of Oral Candidiasis
Figure 21.17b

56. Normal Biota of the Eye Generally sparse Diversity in the bacteria
Corynebacterium is the dominant genus
Eye microbiome resembles that of the skin:
Diphtheroids
Coagulase-negative staphylococci
Micrococcus
Nonhemolytic streptococci
Some yeast
Neisseria species

57. Defenses and Normal Biota of the Eye
Eyes
Mucus in conjunctiva and in tears; lysozyme and lactoferrin in tears
Sparsely populated with
Corynebacterium, Staphylococcus
epidermidis, Micrococcus and Streptococcus species

58. Bacterial Diseases of the Eye
Conjunctivitis
An inflammation of the conjunctiva
Also called pinkeye or red eye
Commonly caused by Haemophilus influenzae
Various other microbes can also be the cause
Associated with unsanitary contact lenses

59. Bacterial Diseases of the Eye
Ophthalmia neonatorum
Caused by Neisseria gonorrhoeae
Transmitted to a newborn's eyes during passage through the birth canal
Prevented by treating a newborn's eyes with antibiotics

60. Neonatal Conjunctivitis
©Medical-on-Line/Alamy

61. Conjunctivitis Disease Table
Neonatal Conjunctivitis
Bacterial Conjunctivitis
Viral Conjunctivitis
Causative Organism(s)
Chlamydia trachomatis or Neisseria gonorrhoeae
Streptococcus pneumoniae,
Staphylococcus aureus,
Haemophilus influenzae,Moraxella, and also Neisseria gonorrhoeae, Chlamydia trachomatis
Adenoviruses and others
Common Modes of Transmission
Vertical
Direct, indirect contact
Virulence Factors
N/A
Culture/Diagnosis
Gram stain and culture
Clinical diagnosis
Prevention
Screen mothers, apply
antibiotic to newborn eyes
Hygiene
Treatment
Topical and oral antibiotics
Gatifloxacin or levofloxacin ophthalmic solution
None, although antibiotics often given because type of infection not distinguished
Distinguishing Features
In babies <28 days old
Mucopurulent discharge
Serous (clear) discharge
Epidemiological Features
Less than 0.5% in developed world; higher incidence in developing world
More common in children
More common in adults

62. Bacterial Diseases of the Eye
Chlamydia trachomatis
Causes inclusion conjunctivitis, or chlamydial conjunctivitis
Transmitted to a newborn's eyes during passage through the birth canal
Spread through swimming pool water
Treated with tetracycline

63. Bacterial Diseases of the Eye
Chlamydia trachomatis
Causes trachoma
Leading cause of blindness worldwide
Infection causes permanent scarring; scars abrade the cornea leading to blindness

64. © Western Ophthalmic Hospital/Science Source
Ocular Trachoma
Chronic infection of the epithelial cells of the eye caused by Chlamydia trachomatis
Major cause of blindness around the world
Several million cases in Africa, Asia, the Middle East, Latin America, and Pacific Islands
© Western Ophthalmic Hospital/Science Source
Ongoing or recurrent infections lead to chronic inflammatory damage and scarring

65. Trachoma Disease Table
Causative Organism(s)
C. trachomatis serovars A–C
Common Modes of Transmission
Indirect contact, mechanical vector
Virulence Factors
Intracellular growth
Culture/Diagnosis
Detection of inclusion bodies in stained preparations
Prevention
Hygiene, vector control, prompt treatment of initial infection
Treatment
Azithromycin or topical
erythromycin
Epidemiological Features
Highest prevalence among children between ages 3 and 5, prevalence as high as 60% in endemic areas

66. Other Infectious Diseases of the Eye
Keratitis
Inflammation of the cornea
Bacteria (U.S.)
Fusarium and Aspergillus (Africa and Asia)

67. Other Infectious Diseases of the Eye
Herpetic keratitis
Caused by herpes simplex virus 1 (HSV-1).
Infects cornea and may cause blindness
Treated with trifluridine