Question

13. Briefly describe the four modes of action of antibacterial drugs and give an example drug for each mode of action. 14. What are the four types of acquired immunity and how do they differ in mechanism? 15. Case Study Question: Mr. B, age 42, is a construction worker in San Antonio. He recently developed a forefoot pedal ulcer, with a high risk of subsequent amputation. His physician referred him for evaluation using the current standard approach to imaging a diabetic foot for infection with a bone scan and/or labelled leukocyte imaging According to the paper by Vangu posted on Blackboard this week, what additional imaging should the nuclear medical department consider doing in Mr. B's case to best ensure that the anatomical detail necessary to distinguish soft-tissue infection from bone infection is best evaluated? What radioisotopes and imaging techniques would be used and how would

Answer 1

13.

1. Inhibit cell wall synthesis (example: penicillin, cephalosporins)

Beta-Lactam antibiotics inhibit the transpeptidase and inhibit cross-linking (provides stability and rigidity of the cell wall). When susceptible bacteria divide in the presence of Beta-Lactam antibiotics -cell wall deficient (CWD) forms are produced.

The interior of the bacterium is hyperosmotic, this cell wall deficiency causes swelling and burst leads to bacterial lysis.

2. Causes leakage from the cell membrane (Amphotericin B, Nystatin)

Amphotericin has some lipophilic properties and interacts with lipopolysaccharide component on the outer membrane of gram-negative bacteria causes destruction of inner and outer membrane leads to the killing of bacteria.

it has not selective toxicity so can damage cell membranes of kidney and nervous system.

3. inhibit protein synthesis( tetracycline, erythromycin)

Drugs bind to the 30S subunit of bacterial ribosomes and thus impair the proofreading of the ribosomal complex. This results in incorrect protein synthesis. when this protein gets into the cytoplasmic membrane kills bacterial cells.

4.inhibitors of nucleic acid synthesis(rifampicin, metronidazole)

metronidazole interferes DNA replication in bacterium

rifampicin blocks RNA polymerase activity in bacteria. Since bacterial RNA polymerase enzyme is different from eukaryotes, it targets only bacterial cell.

14.

four types of acquired immunity:

active immunity is the immunity acquired by natural exposure to a pathogen or by vaccination.

• Naturally acquired active immunity: immunity acquired through continuing or subclinical infection caused by bacteria or virus which is more advantageous than passive immunity.
• Artificially acquired active immunity: immunity acquired through vaccination or administration of toxoids

passive immunity is the immunity acquired by the trans­fer of immune products, like antibody or sensitized T-cells, from an immune individual to non-immune.

• Naturally acquired passive immunity: the immunity acquired by trans-placental transfer of immunoglobulins from mother to fetus.it protects infants for about 6 months after birth.
• Artificially acquired passive immunity: immunity acquired by administering specific anti­bodies or antiserum from one individual to another unimmunized individual, to produce particular antigen in the body.