CH 21: Microbial Diseases of the Skin and Eyes

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1

Perspiration

provides moisture and nutrients for growth

  • Contains salt that inhibits microorganisms
2

Lysozyme

breaks down bacterial cell walls

  • Antimicrobial peptides (ex. b-defensins, Lactoferrin, Bradykinin, etc.)
3

Sebum

secreted by oil glands contains fatty acids that inhibit pathogens

4

Mucous Membranes

  • line the body cavities open to the exterior
  • Tightly packed epithelial cells attached to an extracellular matrix
  • Cells secrete mucus, some cells have cilia
  • Often acidic
  • Membrane of eyes washed by tears containing lysozyme
  • Often folded to maximize surface area
5

Normal Microbiota of the Skin

Resistant to drying and high salt concentration

  • Large numbers of gram-positive cocci: Staphylococci & Micrococci
  • Gram-positive pleomorphic rods (diphtheroids): Propionibacterium acnes inhabits hair follicles; anaerobic & Corynebacterium xerosis occupy the skin surface; aerobic
  • Yeast Malassezia furfur; causes dandruff
6

Exanthem

skin rash arising from a disease

7

Enanthem

rash on mucous membranes arising from a disease

8

Staphylococci:

  • Spherical gram-positive bacteria; irregular clusters.
  • Many produce coagulase. Enzyme clots fibrin.
  • Used to identify types of staphylococci
9

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
10

Staphylococcus epidermidis:

  • Ninety percent of normal skin microbiota.
  • Healthcare-associated pathogen.
  • Produces biofilm on catheters.
  • Coagulase-negative
11

Staphylococcal Skin Infections

  • Folliculitis
  • Sty
  • Furuncle (boil)
  • Carbuncle
  • Impetigo
  • Scalded skin syndrome
  • Toxic shock syndrome (TSS)
12

Group A streptococci (GAS)

Streptococcus pyogenes. Ex: Erysipelas

Produce virulence factors

  • Streptolysins: lyse RBCs
  • M proteins: external to the cell wall; allow adherence and immune system avoidance
13

Streptococcal Skin infections

Gram-positive cocci in chains. Produce hemolysins that lyse red blood cells. Streptococci differentiated into groups A through T

  • Necrotizing fasciitis
14

Warts

  • Papillomas: small skin growths
  • Transmitted via contact
  • Caused by papillomavirus (HPV). Some cause skin and cervical cancers
  • Treated with cryotherapy, electrodesiccation, or salicylic acid
15

Smallpox (Variola)

  • Caused by an orthropoxvirus•Two forms of the disease•Variola major has 20% mortality•Variola minor has <1%
  • Transmitted via the respiratory route, moves into the bloodstream, and infects the skin
  • Completely eradicated from the human population by vaccination•
16

Chickenpox (Varicella)

  • Herpesvirus varicella-zoster (human herpesvirus 3)
  • Transmitted via the respiratory route
  • Causes pus-filled vesicles
  • Reye's syndrome: severe complications of chickenpox; vomiting and brain dysfunction
  • The virus becomes latent in the central nerve ganglia
  • Prevented by a live attenuated vaccine
17

Shingles (Herpes Zoster)

  • Reactivation of the latent varicella-zoster virus that moves along peripheral nerves to the skin
  • Due to stress or lowered immunity
  • Follows the distribution of affected cutaneous sensory nerves
  • Limited to one side of the body
  • Prevention via the zoster vaccine
18

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
  • Usually develop as cold sores or fever blisters
19

Measles (Rubeola)

  • Viral disease transmitted by the respiratory route
  • Cold-like symptoms, macular rash
  • Encephalitis in 1 in 1000 cases
  • Prevented by the MMR (measles, mumps, rubella) vaccine
20

Rubella

  • German measles
  • 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
  • Prevented by the MMR vaccine
21

Conjunctivitis

  • Inflammation of the conjunctiva
  • Commonly caused by Haemophilus influenzae & adenoviruses
  • Can be caused by pseudomonads associated with unsanitary contact lenses
22

Herpetic keratitis

  • Caused by herpes simplex virus 1 (HSV-1)
  • Infects cornea and may cause blindness
  • Treated with trifluridine
23

Trachoma

  • Caused by Chlamydia trachomatis
  • Leading cause of blindness worldwide
  • Transmitted via hand contact or flies•Infection causes permanent scarring; scars abrade the cornea, leading to blindness
  • Oral azithromycin are used in treatment
24

Ophthalmia

  • 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
  • Prevented by treating a newborn's eyes with antibiotics
25

Mycosis

fungal infection of the body

  • Ex: Dermatomycoses
    Tinea capitis Tinea cruris Tinea pedis Tinea unguium
26

Candidiasis

  • Overgrowth of Candida Albicans (yeast)
  • Forms pseudohyphae, making it resistant to phagocytosis
  • Occurs in the skin and mucous membranes of the genitourinary tract and mouth
  • Results, when antibiotics suppress competing bacteria or a change, occurs in the mucosal pH
  • Fulminating (occurs suddenly and escalates quickly) disease in the immunosuppressed