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Skin Diseases – Microbiology Lecture STLCC Online

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Diseases of Body Systems *Skin 


Diseases of the Skin 

I. Normal Skin Flora

A. Large numbers of Gram+ staphylococci

1. Can withstand drying and high salt

2. Corynebacterium xerosis and Propionibacterium acnes

B. Some Gram –

1. Acinetobacter

C. Yeast

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1. Malassezia furfur

a. Yeast responsible for dandruff

D. Larger numbers of bacteria live in moist, nutritive area under arms and between legs

1. Body odor


II. Bacterial Skin Infections

A. Staphylococcal Skin Infections

1. S. epidermidis

a. 90% of normal skin flora

b. Only pathogenic when skin is broken or medical procedure (catheter)

2. S. aureus

a. Most pathogenic

b. Can become resistant to multiple antibiotics, MRSA

c. Folliculitis, sty, boil

d. Impetigo

1) Common, highly contagious, children

e. Toxic Shock Syndrome (TSS)

1) Wearing a tampon too long


B. Streptococcal Skin Infections

1. Produce toxins (hemolysins) that lyse RBC’s

2. α-hemolysins, β-hemolysins, γ-hemolysins

3. β-hemolysis

a. Group A strep (GAS)

1) Rapid spread of infection

2) Streptococcus pyogenes

                                                a) Many diseases

b) Necrotizing fasciitis (flesh eating bacteria)

C. Acne

1. Most common skin infection

2. Propionibacterium acnes

a. Inhabit hair follicles, feed on sebum and clog follicles

b. Sebum production affected by hormones (puberty)

c. Treated with oral antibiotics (tetracycline) or topical gels containing benzoyl peroxide / erythromycin


III. Viral Skin Infections

A. Warts (papillomas)


B. Chickenpox (Varicella) and Shingles (Herpes Zoster)

1. Chickenpox caused by herpesvirus varicella-zoster

2. Respiratory portal of entry, then localizes in the skin

3. After primary infection, the virus remains latent in PNS

a. Later in life stress / compromised immune system may allow the virus to become

active in cutaneous sensory nerves of skin (Shingles)


C. Herpes Simplex Virus (HSV)

1. HSV-1

a. Cold sores or Fever blisters

b. Triggered by stress / compromised immune system

c. Herpetic whitlow – infection of fingers

d. Latent in Trigeminal Nerve

2. HSV-2

a. Genital herpes

b. Latent in sacral nerve

3. HSV-1 and HSV-2 can be spread orally to the genital and vice versa

a. ½ the genital cases in the US is HSV-1 (oral to genital)


D. Measles (Rubeola) and Rubella (German Measles)

1. Respiratory route of entry

2. Measles vaccine

a. MMR (measles, mumps, rubella)


IV. Fungal Skin Infections

A. Cutaneous Mycosis – fungal skin infection

1. Dermatomycoses  – a.k.a. ringworm

a. Tinea capitis – scalp

b. Tinea cruris – jock itch

c. Tinea pedis – athlete’s foot

2. Treated with miconazole and clotrimazole


B. Candidiasis

1. Candida albicans

a. Thrush (mouth) and Vaginitis

2. Disruption of normal bacterial flora can cause candidiasis

3. Increased incidence in AIDS patients, diabetics, obese

4. Treat with topical miconazole, clotrimazole


C. Malassezia furfur – yeast responsible for dandruff

1. Zinc pyrithione (Head and Shoulders®) kills yeast



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