Case Study 2: Beauty and a (Bacterial) Beast
Jenny had never been happy with her nose, and she had saved for three years for
the surgery. She consulted a plastic surgeon, and scheduled surgery for summer
vacation. A few days after surgery
Jenny was changing the dressings of gauze on her nose when she noticed increased
swelling and pain at the incision site. By the next day she had a fever above
100°F. Jenny went back to the surgery clinic, where they took a swab of pus
from the infected area for culture and prescribed an antibiotic. The next day
the lab called to report that Jenny had a Staphylococcus aureus infection.
The surgery and the nasal packing with gauze provided both an area for bacterial
proliferation and an environment that contained air pockets giving the bacteria
necessary amounts of oxygen for growth.
S. aureus is a gram positive, nonmotile, catalase positive, coccus found on the outside of the body, especially around the nose. About 30% of the population carries S. aureus at any particular time, and about 2/3 of people are at least occasional carriers. The bacteria induce localized inflammation that causes capillary endothelial cell damage and gives the bacteria access to the circulation. S. aureus produces an antiphagocytic capsule and surface adhesins. In addition to catalase, it also secretes protease, lipase, and hyaluronidase that destroy tissue, and coagulase that converts fibrinogen to a fibrin clot inside which the bacteria can grow. Many strains of S. aureus produce exotoxins and some strains are antibiotic resistant. Fortunately for Jenny, the S. aureus infecting her nose did not produce toxic shock syndrome toxin or exfoliative toxin, and her infection responded quickly to antibiotics.
1. List as bullets with brief descriptions and in approximate chronological order
the steps in the innate response to a bacterial infection. Include both the cells
and the molecules that are involved in the response to the bacteria and what
each does.
Example:
2. How do phagocytes eliminate pathogens? What group of pathogens are most easily phagocytosed and why?
3. What is inflammation? What are the four signs/symptoms and what causes them? What is the purpose of inflammation? How are leukocytes (neutrophils and macrophages) signaled where to leave the circulation and enter the infection site?
4. What is complement? In what three ways is complement activation initiated and what are the three functions of complement?
5. Of the virulence factors of S. aureus listed below, which promote innate immunity and which protect the bacterium from the immune system? Include in your answer the elements of innate immunity from your list above that are affected by each factor and how. (For example: X stimulates or inhibits phagocytosis, Y activates or blocks a certain activity of complement.)
6. What are acute phase proteins and how do they enhance innate immunity?
7. What is endotoxin shock? How does it differ from inflammation? Was Jenny at risk of endotoxin shock with her Staph infection?
8. Suppose that instead of plastic surgery, Jenny had been bitten by an animal infected with rabies virus. Rabies virus binds to and enters skin cells, where it replicates to produce more virions. Infected cells have rabies virus peptides on their membrane Class I MHC. Compare the innate response to rabies virus at the site of the bite with the innate response to S. aureus. What factors would be the same and what would be specific to virus infections?
Answer the questions and save as a Word document entitled YourNameCase2.doc
(example jdeckerCase2.doc). Send to jdecker@u.arizona.edu as an attachment by
9 AM Thursday June 10. Make sure your name is in the document as well as in
the title.
Supplementary Materials :Innate Immunity, Complement, Cytokines, Infectious Disease, Immunity Rules, Antigen