DISEASES OF THE SKIN AND EYES;WOUNDS AND BITES

CHAPTER 19

Copyright © 2012 John Wiley & Sons, Inc. All rights reserved.

Fig. 19.3 Structures of the eyeFig. 19.4 Lysozyme in tears- The antibacterial action of lysozyme was worked out by Alexander Fleming of penicillin fame.

Tears produced over the eye surface contain antibacterial molecules that inhibit potential infections and drain into the nasal cavity. Most eye infections involve eyelids, conjuctiva or cornea.

do not need to know the structures of the eye

Normal microflora of the skin A huge population of normal microflora colonizes the skin.

1. Oily compounds are metabolized by some microbes, yielding fatty acid by–products that accumulate and give an acidic pH (5.5) to certain parts of the skin. This is a first-line, nonspecific defense against infection.

2. Sweat is rich in sodium chloride which is another important first-line nonspecific defense mechanism.

3. Another important nonspecific line of defense involves the rapid and continuous shedding of skin. As the skin sloughs off it takes colonized bacteria with it.

The majority of organisms living on the skin are Gram positive organisms such as Staphylococcus and Micrococcus and coryneform bacteria ( e.g., Corynebacterium and Proprionibacterium acnes).

Diseases of the SkinBacterial skin diseases-Staphylococcus

aureus- very common organism on the skin and associated with skin infection.

Infection occurs when S. aureus invades the skin through a hair follicle, producing folliculitis (pimples or pustules or sties if at the base of the eyelash).

A larger, deeper, pus-filled infection is an abscess or boil if deeper.

Fig. 19.4 A furuncle. The type of infection is typically caused by Staphylococcus aureus

Furnucle or Boil

Fig. 19.6 Scalded skin syndrome in an infant-cause by S. aureus

Scalded skin syndromeis caused by certain exotoxin-producing strains of S. aureus (the two exotoxins are called exfoliatins

Streptococooal infectionsScarlet fever is caused by Streptococcus pyogenes- which

also causes “strept” throat. Three different erythrogenic toxins that cause scarlet fever have been identified. S. pyogenes is responsible for serious complications including glomerulonephritis and rheumatic fever. Penicillin has appreciably lowered the mortality rate.

The "slapped cheeks" and "white mustache" of scarlet fever.

Erysipelas- is caused typically by Group A hemolytic streptococci (Streptococcus pyogenes).

 

    

                                                                                                                                                                                                  

     

                                                                                                                                                                                                 

Fig. 19.8 Impetigo- highly contagious infection caused primarily by Staphylococci aureus, and sometimes by Streptococcus pyogenes.

Acne (acne vulgaris) affects more than 80 percent of teenagers and many adults. Acne results from secretion of higher than typical levels of sebum from the sebaceous gland. Microorganisms feed on sebum, and ducts of the glands and

surrounding tissues become inflamed . Major causal agent: Propionibacterium acnes,

Burn infections- Burn infections, which are usually nosocomial, account for 80

percent of death among burn patients. Pseudomonas aeruginosa is the prime cause of life-threatening burn infections

Viral Skin Diseases

Other pox diseasesSmallpox- In 1980 the World Health

Organization (WHO) officially proclaimed that smallpox had been eradicated worldwide. This announcement marked the end of centuries of sickness and death from this disease. To this day, smallpox is the only human infectious disease to have been completely eradicated from nature.

This table largely summarizes diseases and causal organisms of the skin; if other material was emphasized during lecture it is fair game for test questions.

Diseases of the Eyes-Bacterial eye diseases-

Ophthalmia neonatorum or conjunctivitis of the newborn, is a pyogenic (pus-forming)

infection of the eyes caused by organisms such as Neisseria gonorrhoeae and

Chlamydia trachomatis. Organisms present in the birth canal enter the eyes as a baby is born. Penicillin once the antibiotic of choice has given way to tetracycline and erythromycin which are effective treatments, but preventive measures (e.g., good hygiene) have greatly reduced the disease in developed countries.

Bacterial conjunctivitis or pink eye- Caused by a wide range of bacteria and viruses- Topically applied sulfonamide ointment is an effective treatment against bacteria.

Trachoma- is caused by specific strains of Chlamydia trachomatis. The

disease is marked by severely swollen conjunctiva . Trachoma is the leading cause of preventable blindness worldwide.

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Table 19.3

Chlamydia trachomatis

Wounds and Bites-Wound infections-

Gas gangrene- C. perfringens (80-90% of cases)

Table 19.4