The skin is comprised of the epidermis, dermis and subcutaneous layers, separated from the underlying muscle by the fascia. (CLICK FOR DIAGRAM). Each layer has different characteristics and a different spectrum of infections. The keratinized layer can be infected by lice, papilloma virus and some fungi. Of the bacterial diseases that infect the skin, impetigo is the most superficial, followed (as one goes deeper into the skin) by erysipelas, cellulitis and fasciitis. A kind of fasciitis called necrotizing fasciitis is often called a flesh-eating infection due to the ability of the causative bacteria to quickly move along the plane of the fascia and cause widespread necrosis. Folliculitis, an infection of the hair follicle, can be quite superficial or form a deeper abscess. Any of the infections except the very superficial can, by toxigenic mechanisms or direct spreading, progress to shock and even death. By far the commonest bacteria causing infections of the skin are Staphylococcus aureus and Streptococcus pyogenes. These can lead to the very serious conditions, toxic shock and toxic shock-like syndrome, but even in the absence of these complications can be very painful and cause widespread damage. Haemophilus influenzae may cause erysipelas or cellulitis, particularly in children, whereas burn infections are most frequently caused by Staphylococcus and Pseudomonas. The enteric bacteria, which have the ability to cause gram negative sepsis, can also be a problem any time there is large scale damage to the skin. The spore-forming anaerobes, the Clostridia, also can cause very dangerous infections including myonecrosis or gas gangrene as well as tetanus that begin by skin penetration. Traumatic infections caused by animal bites or scratches have a unique set of causative agents with rabies being the most feared. Chapter 10, pp 321-342, of Infectious Diseases in 30 Days by F.S. Southwick (McGraw-Hill, 2003) is a comprehensive discussion of skin infections. After reading this, or the appropriate section in your microbiology text, you should be able to answer the following questions.
Question 1 - Single Best Answer
Most skin infections are?
A) contracted from animals
B) spread by the respiratory route
C) contracted from doctors and nurses
D) endogenous infections contracted from bacteria colonizing the skin and nasopharynx
Question 2 - Single Best Answer
What is the causative agent of impetigo?
A) Staphylococcus aureus
B) Staphylococcus epidermidis
C) Streptococcus pyogenes
D) E.coli
E) more than one of the above
Question 3 - Single Best Answer
Which of the following is a predisposing factor for infection of the deeper layers of the skin?
A) trauma
B) surgery
C) diabetes
D) alcoholism
E) all of the above
Question 4 - Single Best Answer
A patient has progressive warmth, redness, swelling, and tenderness of an extremity, but only appears mildly ill. He or she likely has?
A) impetigo
B) cellulitis
C) abscess
D) gas gangrene
E) toxic shock
Question 5 - Single Best Answer
Features that distinguish necrotizing fasciitis from cellulitis include?
A) redness and swelling
B) elevated WBC
C) severe pain in the absence of cutaneous findings
D) crusty vesicles
E) fever
Question 6 - Single Best Answer
Antibiotic ointment applied to the anterior nares is used for which of the following?
A) clear carriage of Staphylococcus aureus
B) impetigo
C) facial cellulitis caused by Haemophilus influenzae
D) sinus infection
E) clenched fist injury
Question 7 - Single Best Answer
A skin abscess or boil is most often caused by?
A) Staphylococcus aureus
B) Staphylococcus epidermidis
C) Streptococcus pyogenes
D) Pseudomonas aeruginosa
E) Clostridium tetani
Question 8 - Single Best Answer
Clostridium tetani is extremely dangerous because?
A) it can grow in the absence of air
B) it can cause gangrene
C) it produces a neurotoxin
D) it is resistant to antibiotics
E) it is a spore forming organism
Question 9 - Single Best Answer
Infections of dog and cat bites are likely to be caused by?
A) Staphylococcus aureus
B) Staphylococcus epidermidis
C) Streptococcus pyogenes
D) Eikenella corrodons
E) Pasteurella sp
Question 10 - Single Best Answer
An annular inflammed scaling patch with a raised margin is caused by?
A) Tinea pedis
B) Trichophyton
C) Staphylococcus aureus
D) Staphylococcus epidermidis
E) Borrelia burgdorferi