Question

Critical Thinking Questions: 5 points (1 point each)

Chapter 19

When and how does our immune system discriminate between self and nonself antigens?

Do people with AIDS make antibodies? If so, why are they said to have an immunodeficiency?

Chapter 20

Which of the following can affect human cells? Explain why.

1. penicillin
2. indinavir
3. erythromycin
4. Polymyxin

Chapter 21

Is it necessary to treat a patient for warts? Explain briefly.

A laboratory test used to determine the identity of Staphylococcus aureus is its growth on mannitol salt agar. The medium contains 7.5% sodium chloride (NaCl). Why is it considered a selective medium for S. aureus?

Clinical Applications: 10 points (2 points each)

Chapter 19

Physicians administering live, attenuated mumps and measles vaccines prepared in chick embryos are instructed to have epinephrine available. Epinephrine will not treat these viral infections. What is the purpose of keeping this drug on hand?

Chapter 20

Vancomycin-resistant Enterococcus faecalis was isolated from a foot infection of a 40-year-old man. The patient had a chronic diabetes-related foot ulcer and underwent amputation of a gangrenous toe. He subsequently developed methicillin-resistant Staphylococcus aureus bacteremia. The infection was treated with vancomycin. One week later, he developed a vancomycin-resistant S. aureus (VRSA) infection. This is the first case of VRSA in the United States. What is the most likely source of the VRSA?

A patient with streptococcal sore throat takes penicillin for 2 days of a prescribed 10-day regimen. Because he feels better, he then saves the remaining penicillin for some other time. After 3 more days, he suffers a relapse of the sore throat. Discuss the probable cause of the relapse.

Chapter 21

A 12-year-old diabetic girl using continuous subcutaneous insulin infusion to manage her diabetes developed a fever (39.4°C), low blood pressure, abdominal pain, and erythroderma. She was supposed to change the needle-insertion site every 3 days after cleaning the skin with an iodine solution. Frequently she did not change the insertion site more often than every 10 days. Blood culture was negative, and abscesses at insertion sites were not cultured. What is the probable cause of her symptoms?

A hospitalized patient recovering from surgery develops an infection that has blue-green pus and a grapelike odor. What is the probable etiology? How might the patient have acquired this infection?

Answer 1

Chapter 19

1. All cells in the human body has cell surface marker known as major histocompatibility complex(MCH) which helps to recognize the self antigen and non self antigen. Normal body cells have intact self antigen, these antigens are recognized by killer cell immunoglobulin receptors and inhibit the attack by natural killer cells. When a non self antigen enters the body,the antigen presenting cells will process then to fragments of peptides and present them on the surface by major histocompatibility complex(MCH). the natural killer cell receptors recognize them because they have difference from self antigen. Then the immune system activates and destroy them.

2.People with AIDS(Acquired immunodeficiency syndrome) make antibodies in their body. Some patients who have AIDS produce antibody against HIV known as broadly neutralizing antibodies (bNABs) within 2 to 12 weeks of infection. The people with AIDS said to be immunodeficient because as the name of the virus itself says  Human immunodeficiency virus ( HIV). It infects CD4+ for lymphocytes which carry CD4+ antigen on their surface. HIV specifically recognize these antigen and destory the CD4+ cells. CD4+ cells are T helper cells which has a major role in immunity. HIV cause massive deficiency of these T lymphocytes and make the person susceptible to many other infection by making the immune system weak . Thus, people with AIDS are said to be immunodeficient.

Chapter 20

Penicillin is a beta lactam antibiotic, which binds on and inhibit an enzyme known as transpeptidase, hence peptidoglycan synthesis (major components of bacterial cell wall) will be inhibited. Peptidoglycan is not present in the human cell wall hence human cells are not effected by penicillin.

Indinavir is an antiviral drug which is active against HIV Type-1. It binds on enzyme protease which cleave the proteins into small fragments required for assembly for the generation of new virus. Indinavir inhibits this enzyme resulting in the formation of immature viral particle which is non-infectious. Since protein assembly not required for human cells, human cells are not affected.

Erythromycin inhibits 50_S sub unit of 70s ribosome and inhibit translocation phase of protein synthesis. Human cells do not have 80s ribosome with 40s and 60s sub units. hence human cells are not affected.

Polymyxins prevents synthesis of fatty acids and disturb the plasma membrane which necessary to maintain osmotic barrier. Because of this activity this also affects the human cells.

Answer is Polymyyxin