Pathophysiology Chapter 19: Microbial Diseases of the Skin and Wounds
I. Structure of the skin
A. overview
1. covers 2m2
2. varies in thickness
3. replaces outer layer about once a month
B. Functions of the skin
1. prevents excessive water loss
2. regulates temperature
3. involved in sensory phenomena
4. barrier against microbial invaders
5. aids in formation of vitamin D
6. helps control microbial invaders through competition
C. Composed of 2 main layers
1. epidermis
a. superficial
b. avascular – no blood vessels
c. 4-5 layers thick – depending on areas subject to abrasion
-stratum basale – deepest- 1 cell layer – attached to underlying dermis
-stratum spinosum – several layers of cells
-stratum granulosum – typically 4-6 cell layers
-stratum lucidum – present only in thick skin – 2-3 cell layers thick
-stratum corneum – outer most - 20-30 layers of dead cells
d. upper layers of dead cells - filled with keratin – waterproof protein
e. outer layer covered with salt and sebum
f. base of epidermis mitotic
2. dermis
a. below epidermis
b. gives skin strength, resiliency, support
c. composed of:
-cells, protein fibers, muscles (arrector pili), sweat (suderiferous) glands,
oil (sebaceous) glands, nerve endings, hair follicles, vascular (blood vessels)
d. below dermis
-hypodermis
-composed of fat and fibers
-function
-cushions, insulates, energy source, anchors skin to underlying tissues
D. Wounds
1. trauma to any tissue of the body
-cuts, scrapes, surgery, burns, bites, etc.
2. allow microbes to infect deeper tissues of body
a. in most cases other body defenses eliminate infection
-blood clot formed
-cells divide and grow into clot
-2nd line of defense kicks in
-phagocytes, complement, inflammation
b. can result in severe or fatal diseases
II. Norma Microbiota of the skin
A. Skin microbiota normally harmless microbes present on skin, hair follicles, and in sweat ducts
1. can’t be completely removed by cleansing
2. body odor – bacteria breaking down sebum and producing waste (arm pits and groin)
2. made of various microbes
a. yeast
-Malassezia
b. bacteria
-Staphylococcus
-Micrococcus
-the diphtheroids
3. may produce disease
-if penetrate epidermis or if immune system is suppressed
III. Bacterial Diseases of the Skin and Wounds
A. Folliculitis
1. signs and symptoms
a. infection of hair follicle
b. often called a pimple
c. called a sty when it occurs at eyelid base
d. spread of infection into surrounding tissues can produce furuncles
e. carbuncles occur when multiple furuncles grow together
2. pathogen and virulence factors
a. most common cause – Staphylococus
-facultative anaerobic, gram-positive bacteria
-cocci typically arranged in clusters
-tolerant of:
- up to 10% NaCl
-dry conditions
-solar radiation
-heat up to and above 600C (1400F) for over 30 minutes
b. 2 species commonly found on skin
-Staphylococcus epidermis – most common – 90% of microbiota
-Staphylococcus aureus – more virulent – often in nose
-enzymes produced making it more virulent
-coagulase – clots blood – pathogen hides in clot
-staphylokinase – dissolves blood clots – pathogen released
-hyaluronidase – dissolves matrix between cells – allows pathogen to spread easily
-lipase – digests fat for food
-β lactamase – conveys resistance to many drugs
c. virulence factors
-enzymes
-protein A – inhibits opsonization/complement cascade
-capsule – inhibits phagocytosis, chemotaxis
-toxins
-cytolytic toxins – disrupts plasma of cells
-leukocidin – kills leukocytes
-inhibitor – makes holes in blood vessels
-exfoliative toxin – shed skin
3. pathogenesis
a. direct contact with person or fomites
b. grows into hair follicles, sebaceous glands
c. triggers fever/inflammation
d. follicle enlarges and fills with pus
e. infection spreads into hypodermis – forms furuncle
f. several neighboring furuncles together – forms carbuncle
g. may spread to blood
-bacteremia
-could lead to endocarditis, osteomyelitis, pneumonia
4. epidemiology
a. S. epidermis
-part of normal microbiota – on all skin
-seldom pathogenic
-can be opportunistic pathogen
b. S. aureus
-not permanent resident
-grows on skin, mucous membrane, moist skin folds (armpits, groin)
5. diagnosis, treatment, and prevention
a. diagnosis
- isolation of gram-positive bacteria in grapelike clusters from pus
b. treatment
-Dicloxacillin – drug of choice (semisynthetic penicillin)
-Vancomycin used to treat resistant strains
c. prevention
- hand antisepsis
-proper procedures in hospitals to minimize MRSA infections
B. Staphylococcal scalded skin syndrome (SSSS)
1. signs and symptoms
a. cells of outer epidermis separate
b. outer epidermis also separates from underlying tissue
c. reddening/wrinkling of skin - begins near mouth spreading over entire body
d. large blisters develop
-fluid lacks bacteria/wbc
e. affected area peels off in sheets
2. pathogen and virulence factors
a. some Staphylococcus aureus strains
b. 1-2 different exfoliative toxins cause SSSS
-causes cells of outer epidermis to separate – dissolves desmosomes
3. pathogenesis
a. blood carries toxins throughout body - toxemia
b. no scarring b/c dermis is unaffected
c. death rate rare – but may be due to secondary infections
4. epidemiology
a. disease occurs primarily in infants
b. transmitted by person-to-person spread of bacteria
5. diagnosis, treatment, and prevention
a. diagnosed by characteristic sloughing of skin
b. treated by administration of antimicrobial drugs
c. widespread presence of S. aureus makes prevention difficult
C. Impetigo (Pyoderma) and Erysipelas
1. signs and symptoms
a. impetigo
-small red flattened patches – mainly on face/limbs
-develops into oozing pus filled vesicles
-forms honey colored crust
-if spreads into lymph nodes with pain and inflammation – now erysipelas
b. erysipelas
-red face, arms or legs
-distinct margin on red patches
-swollen lymph nodes
-pain
-fever
-chills
-leukocytosis
-can be fatal without treatment
2. pathogens and virulence factors
a. most cases caused by S. aureus
b. some cases caused by Streptococcus pyogenes
-gram-positive coccus, arranged in chains
-virulence factors similar to those of S. aureus
-M protein – interferes with complement and phagocytosis
-hyaluronic acid capsule – inhibits phagocytosis
-pyrogenic toxins – cause fever, rash, shock
3. Pathogenesis
-bacteria invade where skin is compromised
4. epidemiology
a. transmitted by person to person contact or via fomites
b. impetigo occurs most in children
c. erysipelas can also occur in elderly
5. diagnosis, treatment, and prevention
a. presence of vesicles filled with bacteria and wbc is diagnostic for impetigo
b. treat with penicillin and careful cleaning of infected areas
c. prevent with proper hygiene and cleanliness
D. Necrotizing fasciitis – “flesh eating strep”
1. signs and symptoms
a. intense pain/swelling at site of infection
b. extremely sensitive to touch
c. fever, nausea, malaise, flu-like symptoms
d. drop in blood pressure – causes confusion
2. pathogen and virulence factors
a. most cases caused by S. pyogenes
b. various enzymes facilitate invasion of tissues
c. exotoxin A and streptolysin S also secreted
-exotoxin A
– causes toxemia
-causes over reaction of immune system
-causes tissue damage
-streptolysin S
-kills many kinds of human cells
3. pathogenesis and epidemiology
a. S.pyogenes enters through breaks in skin
b. usually spread person to person
c. 15% die
4. diagnosis, treatment, and prevention
a. early diagnosis difficult b/c symptoms are nonspecific
b. treat with clindamycin and penicillin
c. affected tissue must be removed
E. Acne
1. pathogen and virulence factors
-commonly caused by Propionibacterium acne - 85% of cases
-gram-positive, rod shaped diphtheriods
-commonly found on skin
2. pathogenesis
a. grows on sebum within sebaceous glands
b. excessive oil production due to hormones stimulates growth of bacteria
c. chemicals secreted attracts wbc and triggers inflammation
d. wbc eat bacteria and more chemicals released with same response
e. dead bacteria/wbc and live wbc make pus – pimple
f. blackhead – plug of dead/live bacteria block pore
g. cystic acne pustules formed
-if rupture can cause scar
h. acne where sebaceous glands most numerous: face scalp, neck, chest, back, shoulders, upper arms
3. epidemiology
a. Propionibacteria are normal microbiota
b. typically begins in adolescence but can occur later in life
4. diagnosis, treatment, and prevention
a. diagnosed by visual examination of skin
b. treated with antimicrobial drugs/drugs causing exfoliation of dead skin cells (benzoyl peroxide)
c. Accutane used to treat severe acne
d. new treatment uses blue-light wavelength to destroy bacteria
F. Cat Scratch Disease
1. signs and symptoms
a. fever
b. malaise
c. swelling at site of infection and nearby lymph nodes
2. pathogen and virulence factors
a. caused by gram-negative bacterium Bartonella henselae
b. endotoxin primary virulence factor
-Lipid A
c. can grow/reproduce in rbc and cells lining blood vessels
3. pathogenesis and epidemiology
a. transmitted by cat bites/scratches or blood sucking arthropods
b. grows intracellularly
c. releases endotoxin when dies – triggers inflammation
4. diagnosis, treatment, and prevention
a. diagnosed with serological testing
b. treated with antimicrobials
G. Pseudomonas Infection – most common microorganism in burn victims
1. signs and symptoms
a. invades bloodstream
b. chills, fever, shock
c. blue-green pigment - pyocyanin
2. pathogen and virulence factors
a. Pseudomonas aeruginosa is causative agent
-Gram- aerobic bacillus
-found in soil, decaying matter, moist environments
b. virulence factors
-adhesins, toxins, polysaccharide capsule, fimbriae, biofilm
c. upon cell death, large amounts of potent endotoxin released
d. exotoxin A and exoenzymes released
-inhibit eukaryotic protein synthesis
e. enzyme elastase
-breaks down elastic fibers
-degrades complement
-breaks apart some immunoglobulins
f. pyocyanin
-triggers 2 reactive forms of oxygen
-these 2 forms contribute to tissue damage
3. pathogenesis
a. infection can occur in burn victims
b. burned area moist warm environment
c. bacteria grows under scab
b. bacteria kills cells, destroys tissue, triggers: fever, inflammation, vasodilation, shock
4. epidemiology
a. P. aeruginosa rarely part of microbiota – rarely causes disease
-can cause infections throughout the body once inside
-infections common in burn victims and cystic fibrosis patients
b. swimmers ear
c. hair follicles infected from contaminated hot tubs
5. diagnosis, treatment, and prevention
a. diagnosis difficult
-pyocyanin discoloration indicates massive infection
b. difficult to treat due to multidrug resistance
-treated with aminoglycoside and antimicrobials
-polymyxin – last resort due to human toxicity
c. P. aeruginosa widespread - infections not typical in healthy individuals
H. Rocky Mountain Spotted Fever
1. signs and symptoms
a. non-itchy spotted rash on trunk and appendages
b. 50% of cases get petechiae - rash develops into subcutaneous hemorrhages
c. fever, headache, muscle pain, nausea, vomiting
d. severe cases
– respiratory, CNS, gastrointestinal, and renal systems fail
-brain infections
-produces delirium, convulsions, language issues, death
2. pathogen and virulence factors
a. caused by Rickettsia rickettsia
b. Gram- aerobic intracellular parasite
c. pathogen avoids digestion in phagosome b/c of capsule
d. dies quickly outside of host
e. needs vector for transmission from host to host
f. enters cell by endocytosis
g. released from phagosome – pathogen secretes enzyme – digests phagosome’s membrane
h. grows/reproduces slowly – divides ever 8-12 hours
i. daughter cells released by exocytosis
3. pathogenesis
a. disease follows due to damage to blood vessels
b. blood leaks from bv
-bp drops
-tissues deprived of O2 and nutrients
c. 5% die
d. if survive, may experience during recovery:
-paralysis of legs
-gangrene
-results in amputation of arms, legs, fingers, toes
-hearing loss
4. epidemiology
-transmitted by bite of infected tick
5. diagnosis, treatment, and prevention
a. initial diagnosis from rash on soles and palms, sudden, fever, headache
b. diagnosis confirmed with serological testing
c. diagnosis crucial b/c treatment often makes difference between life and death
d. treated with various antimicrobials
e. prevention: tick repellents, avoid tick infested areas, protective clothing, remove attached ticks
I. Cutaneous Anthrax
1. caused by Bacillus anthracis – enters wound
2. 3 types
a. gastrointestinal – rare
b. inhalation
c. cutaneous
3. characterized by an eschar
-black, painless, ulcer
4. treated with antimicrobial drugs
5. prevention requires control of disease in animals
a. vaccinate animals
b. destroy infected animals
c. burn or bury carcass
J. Gas gangrene
1. overview
a. blood supply to tissue interrupted – called ischemia
b. tissue becomes anaerobic
c. necrosis sets in
d. if wound infected with anaerobic Clostridium – gas gangrene develops
2. signs and symptoms
a. intense pain at initial site of infection
b. blackening of infected muscle and skin
c. presence of gas bubbles (H2 and CO2)
d. kidney failure
e. shock
f. death
3. pathogens and virulence factors
a. caused by several Clostridium species
-anaerobic Gram+ endospore Bacillus
-most common cause of disease – C. perfringes
b. bacterial endospores survive harsh conditions
-soil, water, sewage, intestines of animals, 1-9% of healthy women’s vaginas
c. vegetative cells secrete 11 toxins
-lyse rbc and wbc
-increases vascular permeability lowering bp
-kills cells
d. rapid growth enables rapid spreading
4. pathogenesis and epidemiology
a. traumatic event must introduce endospores into dead tissue
b. mortality rate exceeds 40%
5. diagnosis, treatment, and prevention
a. appearance is usually diagnostic
b. rapid treatment crucial
-surgical removal of dead tissue
-administration of antitoxin and penicillin
c. prevent with proper cleaning of wounds
IV. Viral diseases of skin and wounds
A. Many viral diseases systemic in nature
-these diseases can result in signs and symptoms in the skin
-poxvirus, herpes infections, warts, chickenpox, shingles, Rubella, measles, Roseola,
cocksackie viral infections, erythema infectiosum
B. Diseases of poxviruses
1. poxviruses that cause human diseases
a. smallpox - human
b. orf, cowpox, and monkeypox - animal
2. smallpox 1st human disease eradicated
3. signs and symptoms – progresses through series of stages
a. flat reddened macules
b. become raised sores – papules
c. fill with clear fluid – vesicles
d. fill with pus – pustules or pox
e. dry and form crust
f. possible scarring b/c dermis involved
g. fever (up to 1070F), malaise, delirium, prostration, possible blindness if infects eye