Download Spring 2015-Chapter 19

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 eye
do not need to know the structures of
the eye
Fig. 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.
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 Skin
Bacterial 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.
Furnucle or Boil
Fig. 19.4 A furuncle. The type of infection is typically caused by Staphylococcus aureus
Scalded skin syndrome
is caused by certain exotoxinproducing strains of S. aureus
(the two exotoxins are called
exfoliatins
Fig. 19.6 Scalded skin syndrome in an infant-cause by S. aureus
Streptococooal infections
Scarlet 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 diseases
Smallpox- 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 EyesBacterial eye diseasesOphthalmia 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.
.
Chlamydia trachomatis
Table 19.3
Wounds and BitesWound infectionsGas gangrene- C. perfringens (80-90% of cases)
Table 19.4