BIO 150 chapter 21

Chapter 21: Microbial Diseases of the Skin and Eyes

Structure and Function of the Skin

  • Learning Objective 21-1: Describe the structure of the skin and mucous membranes and the ways pathogens can invade the skin.

  • Epidermis: Thin outer portion of skin, composed of layers of epithelial cells.

  • Keratin: Waterproofing protein coating outer layer of epidermis.

  • Dermis: Inner, thick portion of skin primarily composed of connective tissue.

Skin Diagram Overview

  • Key Structures:

    • Hair follicle

    • Oil gland (produces sebum)

    • Hair shaft

    • Stratum corneum

    • Sweat pores

    • Blood vessels

    • Adipose (fat) tissue

    • Nerve tissue

Functions of Skin and Mucous Membranes

  • Perspiration:

    • Provides moisture and nutrients promoting microbial growth.

    • Contains salt, inhibiting microorganisms.

    • Contains lysozyme, which breaks down bacterial cell walls.

    • Sebum contains fatty acids that inhibit pathogens.

Mucous Membranes

  • Line body cavities open to exterior with tightly packed epithelial cells attached to an extracellular matrix.

  • Cells secrete mucus, some have cilia, often acidic.

  • Membranous areas (like eyes) are washed by tears containing lysozyme.

  • Folded structures maximize surface area.

Normal Microbiota of the Skin

  • Learning Objective 21-2: Provide examples of normal skin microbiota and their roles.

  • Resistant to drying and high salt concentrations, large numbers of gram-positive cocci (staphylococci, micrococci) present.

  • Moist areas have higher populations that metabolize sweat, contributing to body odor.

  • Notable Microbiota:

    • Cutibacterium acnes: inhabits hair follicles, produces acids maintaining low skin pH.

    • Corynebacterium xerosis: occupies skin surface; aerobic.

    • Malassezia furfur: yeast causing dandruff.

Microbial Diseases of the Skin

  • Learning Objectives:

    • Differentiate between staphylococci and streptococci.

    • List skin infections caused by each.

    • Understand diseases like chickenpox, shingles, cold sores, measles, and rubella.

Lesions and Rashes

  • Vesicles: Small, fluid-filled lesions.

  • Bullae: Larger vesicles (>1 cm).

  • Macules: Flat, reddened lesions.

  • Papules: Raised lesions.

  • Pustules: Raised lesions with pus.

  • Exanthem: Skin rash arising from disease.

  • Enanthem: Rash on mucous membranes from disease.

Staphylococcal Skin Infections

  • Staphylococci: Gram-positive bacteria forming clusters, many produce coagulase (clots blood).

  • Staphylococcus epidermidis: Major normal skin flora, coagulase-negative, forms biofilm on catheters.

  • Staphylococcus aureus: Carried in nasal passages; produces toxins, can cause sepsis, MRSA strains are antibiotic-resistant.

Staphylococcal Infections

  • Folliculitis: Hair follicle infection.

  • Sty: Folliculitis of an eyelash.

  • Furuncle: Abscess of localized pus.

  • Carbuncle: Severe tissue inflammation from an infected furuncle.

  • Impetigo: Crusty sores caused by impetigo; spread by autoinoculation.

  • Toxic shock syndrome (TSS): Systemic illness linked to a toxin in the bloodstream.

Streptococcal Skin Infections

  • Characteristics: Gram-positive cocci in chains, produce hemolysins.

  • Group A Streptococcus (GAS): Causes diseases like erysipelas and necrotizing fasciitis.

    • Virulence factors: Streptolysins, M proteins, hyaluronidase, and streptokinases for tissue invasion.

Acne

  • Most common skin ailment, linked to shed skin cells and sebum blockage.

  • Influenced by hormones rather than diet.

    • Comedonal acne: Mild, treated with topical treatments.

    • Inflammatory acne: Caused by Propionibacterium acnes leading to inflammation.

    • Nodular cystic acne: Severe with deep inflamed lesions.

Viral Diseases of the Skin

  • Often transmitted via respiratory routes; affect children and fetuses.

  • Warts: Caused by papillomaviruses.

  • Chickenpox (Varicella): Pus-filled vesicles, can lead to shingles (herpes zoster) upon reactivation.

  • Herpes Simplex: HSV-1 and HSV-2; can manifest as cold sores.

Measles and Rubella

  • Measles (Rubeola): Transmitted respiratory; causes rash and complications like encephalitis.

  • Rubella (German Measles): Causes mild rash; dangerous for fetuses, preventable by the MMR vaccine.

Fungal Diseases of the Skin

  • Cutaneous mycoses: Fungi like Trichophyton, Microsporum, treated with topical antifungals.

  • Subcutaneous mycoses: More severe; invade deeper skin layers.

Microbial Diseases of the Eye

  • Conjunctivitis: Inflammation of conjunctiva, caused by Haemophilus influenzae or adenoviruses.

  • Ophthalmia Neonatorum: Caused by Neisseria gonorrhoeae, preventing blindness through antibiotic treatment.

  • Inclusion Conjunctivitis: Resulting from Chlamydia trachomatis, often in newborns or due to contaminated water.