1. Microbial diseases of the Skin
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

2. Micro Chapter 18
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

3. Fig. 18.1

4. Fig. 18.2, Impetigo

5. Staph and Strep on blood agar

6. Micro Chapter 18 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

7. Micro Chapter 18
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)

8. Micro Chapter 18 Coagulase test

9. Micro Chapter 18 Rapid Staph tests

10. Micro Chapter 18 Staph: SSSS

11. Micro Chapter 18 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

12. Micro Chapter 18 Staph: Boil, Carbuncle
Staph; skin infections, danger – toxemia, septicemia

13. Staph - Furuncle, Carbuncle

14. Micro Chapter 18 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)

15. Drug resistant Staph; MRSA
Micro Chapter 18
Drug resistant Staph; MRSA

16. Micro Chapter 18

17. Micro Chapter 18
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

18. Micro Chapter 18
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)

20. Micro Chapter 18
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

21. Micro Chapter 18 Page 539.2

22. Micro Chapter 18
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

23. Micro Chapter 18
gangrene

25. Micro Chapter 18
Hyperbaric set up

26. Micro Chapter 18
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

27. Micro Chapter 18
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

29. Micro Chapter 18 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

30. Micro Chapter 18 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

31. HSV 1, HSV 2

32. 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)

33. Measels Rash Congenital rubella

34. Micro Chapter 18
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.

35. Micro Chapter 18, Scalp ringworm

36. Micro Chapter 18, Ringworm of body

37. Micro Chapter 18 – tinea pedis

38. Micro Chapter 18: Tricophyton, M. canis, Epidermophyton

39. Micro Chapter 18
Candida albicans – yeast infection, candidiasis, in infants causes thrush, common cause of
vaginitis - miconazole, clotrimazole

40. Micro Chapter 18 Eye diseases:
1. Conjunctivitis – Trachoma Chlamydia trachomatis
2. Neonatal conjunctivitis by Chlamydia and N. gonnorrhea
3. Viral - adenoviruses

41. Fig. 18.21, Neonatal conjunctivitis

42. Fig Trachoma