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Micro Chapter 18
Microbial diseases of the Skin
Structure of skin
Epidermis
Dermis
Pathways into deeper tissues – hair follicles
and sweat glands
Normal flora – skin has many microbes
present as commensals, can be
opportunistic pathogen if
the skin is breached
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1. These microbes are adapted to dry
conditions and even the fatty acids that
inhibit most other microbes.
Ex. Staphylococcus and Micrococcus
2. Other genera – Corynebacterium and
Propionobacterium
Fig. 18.1
Fig. 18.2, Impetigo
Staph and Strep on blood agar
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Bacterial diseases of the skin :
1. Staphylococcal skin infections - S. Aureus, has
some highly virulent strains
A. Gram + cocci, catalase +, coagulase +,
beta hemolytic, golden yellow colonies
on nutrient agar
B. The commensal staph are usually
catalase and coagulase negative – S.
epidermididis
C. Pathogenic staph can produce dangerous
toxins
i. Leukocydin – kills leukocytes
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ii. Exfoliate toxin – causes skin to separate and peel
away – (SSSS) – staph scalded skin syndrome
(pg.), bacteriophage dependent toxin (toxemia)
iii. Coagulase – fibrin clots, shield staph from
phagocytes
iv. Entero toxin – exotoxin that causes FBI
symptoms in the intestinal tract
v. Toxic shock toxin 1 – life threatening disease,
toxin enters blood stream, causes symptoms of
fever, vomiting, skin rash and deadly shock
(originally diagnosed and associated with use of
vaginal tampons – now associated with surgical
procedures using packing or post childbirth
complications)
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Coagulase test
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Rapid Staph tests
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Staph: SSSS
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D. Pathogenesis on skin
i. Folliculitis – infection of hair follicles
(pustules)
ii. Boils and carbuncles – deeper more
serious infection of hair follicle – treat
by lancing and draining, penicillins
iii. Abscesses – deep pustular lesions, can
be serious, can invade deep into
tissue and causes blood stream infection
(septicemia)
iv. Impetigo (really a four letter word) in
hospital nurseries and daycares,
reason for use of hexachlorophene
disinfectants
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Staph: Boil, Carbuncle
Staph; skin infections, danger – toxemia,
septicemia
Staph - Furuncle, Carbuncle
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E. Drug resistance is a real problem with
Staph
i. Many are penicillin resistant, artificial
penicillins – methicillin resistant
strains are appearing
ii. Cephalosporins are used (resistant
to penicillinases)
iii. Vancomycin is drug of last resort,
now a few strains resistant to
vancomycin (Detroit area)
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Drug resistant Staph; MRSA
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2. Streptococcal skin infections – gram +
cocci, usually in chains,
A. Group a beta hemolytic strep (S.
pyogenes)
B. Erysipelas – serious infection by
Strep of the skin, can spread and even
cause septicemia – treatable with
penicillin type drugs
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Beta hemolytic Strep
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C. Impetigo – local skin infections (often
with Staph), spread easily on contact
and spreads among children in day cares
(page)
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• D. Remember Strep has several virulence
factors (hyaluronidase, streptokinases,
• hemolysins, etc.)
• E. Group a Strep – associated with the
necrotizing fascitis – flesh eating Strep,
– exotoxin a seems to be associated, deep
tissues involved (cellulitis, myositis,
– muscle coverinng – fascia) see pg 551
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Page 539.2
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• 3. Clostridium perfringens – gram+ anaerobic
spore forming rod shaped bacteria
• A. Gas gangrene – (pg. 549) infection occurs
after skin is punctured, the organism
• produces an alpha toxin that kills cells, and then dead cells
are substrate for
• more growth, more toxin, more dead tissue, rapid spreading
of disease
• B. Treat with debridement of dead tissue and
hyperbaric chamber (get oxygen deep into
tissues), penicillin type antibiotic
• C. Can grow in high protein food that is low in
oxygen and causes FBI
– (enterotoxin) gravies, stews, thick meat dishes - out of
temperature for too long
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• gangrene
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• Hyperbaric set up
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• 4. Leprosy – Hansen’s disease,
Mycobacterium leprae, stains acid fast
like tubercle bacilli,
• strict human parasite, not able to culture it, was
cultured in Armadillos so that it could be
• studied and antigens harvested for evaluation and
development of ?vaccine?
• A. Not very virulent, slow progression
• B. Tuberculoid form, minor skin damage, but can
cause nerve damage
• C. Lepromatous form, gross disfigurement – see
page 552 lepromas
• D. See checkpoint 18.6
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• Leprosy; awful
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• Viral infections
• 1. Warts – papillomas , many different
viruses
• 2. Variola – smallpox, see text - biological
warfare and mandatory vaccination?
• 3. Varicella – chickenpox, and shingles
• Warts
Variola
Varicella
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a. Chickenpox is relatively mild childhood disease
b. Herpes type virus, acquired by respiratory system and then localizes
in the skin
c. Forms vesicles in skin, fill with pus, and then rupture
d. Chickenpox in adults can be serious and if acquired early in
pregnancy can cause serious fetal damage
e. Since it is a herpes type virus can become latent, later it can erupt into
serious
disease in adults called shingles
i. Latent in peripheral nerve ganglia
ii. Triggers can be stress or aging, the virus outbreak occurs
along the
peripheral nerves, about the waist and even face and scalp very
painful
iii. Immunocompromised patients, may be fatal
f. Vaccine now seems effective
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• 4. Herpes simplex viruses – HSV-1 and HSV-2
– A. H4. Herpes simplex viruses – HSV-1 and HSV-2
– A. HSV – 1 cold sores (fever blisters) most acquire it
infancy, respiratory or oral route,
– latent virus activated by stress, UV light etc.,
– B. HSV – 2 similar virus spread by sexual contact –
genital herpes – 1 cold sores (fever blisters) most
acquire it infancy, respiratory or oral route,
• latent virus activated by stress, uv light etc.,
• B. HSV – 2 similar virus spread by sexual
contact – genital herpes
HSV 1, HSV 2
Measels
• 5. Rubella – german measles, mild childhood
disease
– A. Good vaccine available (MMR.) Checkpoint 18.8,
pg 563
– B. Can pass placental barrier and cause serious
deformities or death of fetus
• 6.Rubeola – red measles, good vaccine
available (MMR), some children are not
vaccinated in the inner city areas, see measles
outbreaks
– A. Can be very serious disease in infants and elderly
• B. Secondary bacterial infections are a problem
(pneumonia)
Measels
Rash
Congenital rubella
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• Dermatophytes – fungal infections of the skin –
griseofulvin, miconazole sse pg 568, checkpoint
• 18.11
– 1. Mycosis – fungal infection
– 2. Cutaneous infection – dermatophytes grow on
moist skin using keratin in skin as substrate
– 3. Tineas or ringworms scalp – tinea capitis, tinea
cruris – groin, tinea pedis- feet (athletes foot)
• 4. Tricophyton spp., Microsporium spp.,
Epidermophyton spp.
Micro Chapter 18, Scalp ringworm
Micro Chapter 18, Ringworm of body
Micro Chapter 18 – tinea pedis
Micro Chapter 18: Tricophyton, M. canis,
Epidermophyton
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• Candida albicans – yeast infection,
candidiasis, in infants causes thrush,
common cause of
• vaginitis - miconazole, clotrimazole
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•
Eye diseases:
1. Conjunctivitis – Trachoma Chlamydia trachomatis
2. Neonatal conjunctivitis by Chlamydia and N.
gonnorrhea
3. Viral - adenoviruses
Fig. 18.21, Neonatal conjunctivitis
Fig. 18.22 Trachoma