Chapter 21 - Microbial Disease of the Skin and Eyes

Unit 3

How does perspiration (sweat) protect the skin?

Provides moisture and nutrients for some bacteria; contains salt and dermicidin, which inhibits microbes.

How does lysozyme protect the skin

Breaks down bacterial cell walls; found in tears, saliva, mucus.

How does sebum protect the skin?

Creates a slightly acidic barrier and contains fatty acids that inhibit Gram-positive bacteria.

How do mucous membranes protect the body?

Secrete mucus, often acidic; cilia in some cells move microbes; tears wash eyes.

What is normal skin flora?

Gram-positive cocci resistant to drying and high salt; mainly Staphylococci (S. epidermidis) and Corynebacteriaceae.

Which Staphylococcus species is more prevalent on skin?

S. epidermidis (~90% of normal skin flora); usually harmless but opportunistic.

Which Staphylococcus species is more problematic?

S. aureus; less common, more virulent, coagulase-positive, produces toxins, includes MRSA (Methicillin-Resistant Staphylococcus aureus)

What are examples of S. aureus skin infections?

Folliculitis, sty, furuncle (boil), carbuncle, impetigo.

Which Streptococcus species causes skin infections?

Group A Streptococcus (S. pyogenes).

What serious skin infection can S. pyogenes cause?

Necrotizing fasciitis (flesh-eating disease) via exotoxin A.

Characteristics of Pseudomonas aeruginosa?

Gram-negative, aerobic rod; produces exotoxins, endotoxins, and pyocyanin (blue-green pus).

Infections caused by Pseudomonas aeruginosa?

Swimmer’s ear, hot tub folliculitis, opportunistic burn infections; biofilm delays healing.

Why is HPV special? (Part 1)

Causes papillomas (skin growths), transmitted skin-to-skin, most common STD.

Why is HPV special? (Part 2)

>50 types; some can cause cancers (cervical, throat, anal, penile); preventable with vaccines.

Smallpox – why is it noteworthy? (Part 1)

Caused by variola virus; high mortality (major: 20–60%, minor: <1%).

Smallpox – why is it noteworthy? (Part 2)

Transmitted via respiratory route; survivors often have deep-pitted scars; eradicated by vaccination.

What is viral latency?

Virus remains dormant in nerve ganglia after initial infection.

Example of a latent virus?

Varicella (chickenpox) → reactivates later as shingles.

Difference between HSV-1 and HSV-2?

HSV-1: oral/respiratory, latent in trigeminal ganglia.
HSV-2: sexual transmission, latent in sacral ganglia.

Measles hallmark sign and vaccine?

Koplik’s spots inside the mouth; prevented by MMR vaccine.

Hand-foot-and-mouth disease – unique symptom?

Rash on hands, feet, mouth, and tongue; fever and sore throat.

Ringworm – fungal or helminth?

Fungal infection (mycosis), colonizes hair, nails, and outer epidermis.

Examples of ringworm infections?

Tinea capitis (scalp), tinea cruris (jock itch), tinea pedis (athlete’s foot), tinea unguium (nails).

What is impetigo?

Crusting sores on skin, spread by autoinoculation (self-inoculation).

What is Toxic Shock Syndrome (TSS)?

Fever, vomiting, shock, organ failure, rash, desquamation caused by TSST-1 toxin from S. aureus.

What type of exotoxin does S. pyogenes produce for necrotizing fasciitis?

Exotoxin A, acts as a superantigen.

What makes Pseudomonas aeruginosa infections difficult to treat?

Produces biofilms, resistant to many antibiotics, delays wound healing.

Name one toxin unique to Pseudomonas aeruginosa.

Pyocyanin – blue-green pigment, depresses immune response, causes neutrophil apoptosis.

HPV transmission route?

Skin-to-skin contact; sexually transmitted for some types.

How is smallpox transmitted?

Respiratory route → bloodstream → infects skin

What was the outcome of smallpox eradication?

Completely eradicated via vaccination; survivors often had deep scars

What is the difference between chickenpox and shingles?

Chickenpox = initial infection; shingles = reactivation from latent virus in nerve ganglia.

HSV-1 latency location and triggers?

Trigeminal nerve ganglia; triggered by sun, stress, hormonal changes

HSV-2 latency location and transmission?

Sacral nerve ganglia; transmitted primarily sexually.

Measles hallmark sign?

Koplik’s spots – red/white spots on oral mucosa opposite molars.

Vaccine for measles?

MMR (measles, mumps, rubella) – live attenuated.

Ringworm – what part of the body does it infect?

Hair, nails, outer epidermis; metabolizes keratin.