Untitled Quiz

Introduction

• Skin acts as a physical barrier against microorganisms
• Moist skin areas have larger bacterial populations compared to dry areas

Structure and Function of the Skin

• Outer skin layer (epidermis) contains keratin, a waterproof material
• Inner skin layer (dermis) contains hair follicles, sweat ducts, and oil glands allowing microorganisms to pass through
• Sebum and perspiration inhibit microbial growth, but also provide nutrients to some microorganisms
• Epithelial cells lining body cavities secrete mucus, forming a mucous membrane

Normal Microbiota of the Skin

• Skin microorganisms tolerate desiccation and high salt concentrations
• Gram-positive cocci are predominant skin microbes
• Normal skin microbiota is not fully removed by washing
• Cutibacterium metabolizes oil and colonizes hair follicles
• Malassezia furfur yeast grows on oily secretions, and may cause dandruff

Microbial Diseases of the Skin

• Vesicles are small fluid-filled lesions; bullae are larger than 1 cm, macules are flat, reddened lesions, papules are raised lesions, and pustules are raised lesions that contain pus
• Most skin microbiota consists of coagulase-negative Staphylococcus epidermidis
• Almost all pathogenic S. aureus strains produce coagulase
• Pathogenic S. aureus produces enterotoxins, leukocidins, and exfoliative toxin
• Localized infections, impetigo, toxemia, and staphylococcal toxemias (e.g., scalded skin syndrome, toxic shock syndrome) can result from skin infections
• Group A beta-hemolytic streptococci produce virulence factors like M protein, deoxyribonuclease, streptokinases, and hyaluronidase, causing tissue destruction
• Pseudomonas aeruginosa produces endotoxins and several exotoxins causing otitis externa, respiratory infections, burn infections, and dermatitis; characterized by blue-green pus
• Mycobacterium ulcerans causes deep-tissue ulceration
• Cutibacterium acnes metabolites cause inflammatory acne

Viral Diseases of the Skin

• Papillomaviruses cause skin cell proliferation, forming warts (papillomas)
• Warts spread through direct contact and can regress spontaneously or be removed
• Variola virus causes variola major and minor skin infections
• Smallpox is transmitted via the respiratory route and bloodstream; eradicated
• HHV-3 (varicella-zoster virus) causes chickenpox and shingles. Chickenpox can cause complications such as encephalitis and Reye's syndrome
• Shingles is a reactivation of varicella-zoster virus, characterized by a vesicular rash along the affected cutaneous sensory nerves

Herpes Simplex Virus Infections

• Herpes simplex virus (HSV-1) infection of mucosal cells results in cold sores and, less commonly, encephalitis; transmitted primarily through oral and respiratory routes
• Herpes encephalitis occurs when herpes simplex viruses infect the brain, with acyclovir showing successful treatment
• Herpes simplex virus remains latent in nerve cells, allowing recurrences of cold sores

Measles

• Measles virus causes measles infection, is transmitted by respiratory route
• Macular lesions appear on the skin after the incubation period in the upper respiratory tract.
• Complications of measles include middle ear infections, pneumonia, encephalitis, and secondary bacterial infections

Rubella

• Rubella virus transmitted by the respiratory route, leading to a red rash and mild fever
• Congenital rubella syndrome can result if a woman contracts rubella during the first trimester of pregnancy

Fungal Diseases of the Skin and Nails

• Microsporum, Trichophyton, and Epidermophyton cause dermatomycoses (e.g., ringworm, tinea)
• Fungi colonize keratin-containing structures (hair, skin, nails)
• Diagnosis involves microscopic examination of scrapings or fungal cultures
• Sporotrichosis results from soil fungi penetrating the skin through wounds
• Candida albicans causes oral thrush and vaginitis

Parasitic Diseases of the Skin

• Scabies is caused by mites burrowing and laying eggs in the skin
• Pediculosis involves infestation by Pediculus humanus

Microbial Diseases of the Eye

• Conjunctivitis is caused by bacterial transmission from skin and upper respiratory tract, or through contact lenses
• Ophthalmia neonatorum is caused by Neisseria gonorrhoeae transmission from mother to infant during birth
• Inclusion conjunctivitis results from Chlamydia trachomatis infection , often transmitted through unchlorinated water during birth,
• Trachoma is transmitted by hands, fomites (inanimate objects), and perhaps flies
• Fusarium and Aspergillus fungi, herpes simplex virus (HSV-1), and Acanthamoeba protozoa can also infect the eye, potentially causing corneal ulcers, and other forms of keratitis.