Chapter 21. Skin and Eye Infections

A. Bacterial Infections:

1. Skin: physical barrier, prevent infections, also

•       Sweat (has salts, lysozyme, antimicrobial peptides)

•       Sebum (oil that feed commensal bacteria)

•       Microbiota (commensal bacteria that outcompetes pathogens)

2. Skin infections: many caused by opportunistic microbes (most common: S. aureus, Staph epi,

    Streptococcus). Staph aureus distinguished from Strep infections because S. aureus is catalase positive.

    Staph skin infections:

Ø  Folliculitis: bumps and pimples that may be itchy, red, may contain pus

Ø  Furuncles (boils)

Ø   Carbuncles (deeper abscesses)

3. Tears have:

•       Lysozyme

•       Defensins (antimicrobial)

•       Lactoferrin

•       Mucin (hydrates eye)

4. Conjunctivitis: infection of the conjunctiva (pink eye)

5. MRSA (Methicillin-Resistant Staph Aureus): Opportunistic and very contagious infection. Strain is  

    resistant to many antibiotics. Prevalent in health-care settings (hospitals, nursing homes) and it's  

    known as health care-associated (HA-MRSA). HA-MRSA infections are associated with invasive surgical

    procedures or devices, such intravenous tubing or artificial joints. HA-MRSA can also spread by health

    care workers.

   Another type is community-associated (CA-MRSA), often starts as a painful skin boil. CA-MRSA usually

   spreads by skin-to-skin contact. More common in athletes and people who live in crowded conditions

   (military).

6. Streptococcus pyogenes bacteria: have many virulence factors that help establish an infection:

•       Streptolysins                        damage       

•       Hyaluronidase                      tissue

•       Streptokinase                      prevent

•       M-protein                            phagocytosis

•       Capsule

7. Skin Streptococcus infections:

•       Cellulitis: painful, red rash on skin

•       Erysipelas: large very inflamed patch of the dermis causes raised rash with clear borders

•       Erythema nodosum: inflammation in the fat cells of the hypodermis; characterized by red lumps or nodules, usually on the lower legs

8. Necrotizing Fasciitis: Streptococcus pyogenes infection that start in the skin and spread.

v  Rare, potentially life-threatening condition

v  sometimes referred to as flesh-eating bacterial syndrome

v  Virulence factors:

·       Invasins: allow bacteria to attach to tissues

·       Proteases: enzymes that destroy tissue and inactivate complement

v  Treatment: debridement (surgical removal of dead or infected tissue) or amputation to stop the spread of the infection and intravenous antibiotics

v  Other organisms that can cause it:  Klebsiella, Clostridium, E. coli, S. aureus

9. Pseudomonas aeruginosa, a gram-negative aerobic bacillus common in water, soil and human skin.

·       Common cause of opportunistic infections of wounds and burns

·       Can cause hot tub rash, in users of pools and hot tubs

·       Cause of otitis externa, an infection of the ear canal that causes itching, redness, and discomfort, and can progress to fever, pain, and swelling

10. Propionibacterium acnes: feed on sebum; secrete enzyme that damage hair follicle and cause lesions

      (pimples).

11. Anthrax: Zoonotic infection caused by Bacillus anthracis

•       B. anthracis, a gram-positive, spore-forming, facultative anaerobe

•       Anthrax mainly affects animals such as sheep, goats, cattle, and deer, but can affect humans as well.

•       the spores are found in soil and survive for years

•       Most anthrax cases occur when spores enter the body through cuts in the skin (cutaneous anthrax)

B. Viral infections:

12. Papilloma (warts) are common skin infections caused by human papillomavirus (HPV) and are

      transmitted by direct contact.

•       There are many types of HPV:  common warts, plantar warts, flat warts, and filiform warts (long).

•       HPV can also cause sexually-transmitted genital warts.

•       Vaccine for some strains of HPV

13. Herpes (skin and eye).  Two types:  HSV-1 and HSV-2.

Ø  HSV-1 is transmitted by direct contact, and is associated with oral herpes.

Ø  HSV-2 is usually transmitted sexually and is associated with genital herpes.

Ø  incidence of genital HSV-1 and oral HSV-2 infections has been increasing in recent years.

14. Roseola: mild viral disease caused by Herpes 6. More common in children. Resolves on its own. Symptoms:  Fever, runny nose, sore throat, rash on chest and abdomen.

15. Fifth disease: caused by Parvovirus; very contagious; most common in children; symptoms similar to a cold; acquired through respiratory droplets, can cause rash in face and body; resolves on its own.

16. Fungal infections (mycoses):       

•       Cutaneous mycoses (superficial infections of the epidermis, hair, and nails)

•       Subcutaneous mycoses (penetrate the epidermis and dermis)

•       Systemic mycoses (spread throughout body)

17. Tineas: fungal infection of the skin.

Ø  Cutaneous mycoses caused by dermatophytes, fungi that feed on keratin (protein in skin, hair, and nails.

Ø  Tineas are generally called ringworm, but tineas in specific locations have distinctive names:

•       Tinea corporis (ringworm)     Body

•       Tinea capitis (ringworm)        Scalp

•       Tinea pedis (athlete’s foot)     Feet

•       Tinea barbae (barber’s itch)   Beard

•       Tinea cruris (jock itch)             Groin