Microbiology - Antibiotics

  1. Which of the following antimicrobials are bacteriostatic? (multiple answers)

    a. Trimethoprim
    b. Clindamycin
    c. Vancomycin
    d. Tetracycline
    Trimethoprim, Clindamycin, Tetracycline

    Vancomycin is bactericidal
  2. Which of the following antimicrobials are bactericidal? (multiple answers)

    a. Penicillin
    b. Vancomycin
    c. Gentamicin
    d. Erythromycin
    Penicillin, Vancomycin, Gentamicin

    Erythromycin is bacteriostatic
  3. The smallest concentration of antimicrobial agent that prevents growth in subvulture is the definition of:

    B. Minimum bactericidal concentration
  4. What is the normal function of the Penicillin binding proteins (PBPs)?

    B. Cross links used to hold building blocks of the bacterial cell wall together
  5. In the Kirby-Bauer disk diffusion susceptibility test, which variable(s) are critical when testing for antibiotic susceptibility?

    E. All of the above
  6. Why are gram negative organisms less susceptible to Vancomycin than gram positive organisms?

    D. The peptidoglycan layer of gram negative bacteria is very large, preventing the large Vancomycin molecule from passing through
  7. What does a beta lactam ring look like?
    Image Upload 1
  8. What makes different beta-lactam antibiotics unique from one another?
    • By changing the R groups on the left side of these drugs, the spectrum of activity can be altered. The ring attached to the right of the beta lactam ring also makes these drugs unique.
    • Ex. a 5 membered ring is found in Penicillins and Carbapenems. A 6 member ring is found in the Cephalosporins. Sulbactam, a beta lactam "decoy" lacks R groups and therefore beta lactam activity as well.
  9. What is beta lactamase and what is its site of action? What is the end result of this enzymatic action?
    • Beta lactamase is an enzyme produced by bacteria that inactivates beta lactam by hydrolyzing (cleaving) the beta lactam ring.
    • A beta lactam drug is inactivated once its beta lactam ring is broken. It no longer can bind with the PBPs and will have no effect on the bacteria cell wall
  10. What is the mechanism of action of beta-lactamase inhibitor?

    C. Irreversibly binds to the active site of the beta-lactamase, protecting the antibiotic from its action
  11. Which of the following are beta-lactamase inhibitors?

    A. Sulbactam, Clavulanic Acid, Tazobactam
  12. Which of the following are beta-lactamase stable penicillins?

    D. Oxacillin

    Ampicillin is extended spectrum, Penicillin K is beta lactamase susceptible, and Clindamycin is for protein synthesis inhibition (not a Penicillin)
  13. Explain how certain organisms escape damage from beta lactamase stable penicillins (how are they resistant to these agents?)
    When some organisms are unable to inactivate the drug with their beta lactamase enzymes, they resort to other methods. Some will just overproduce their cell wall components in order to "outnumber" the drug. Others may alter their target site by finding new ways to synthesize their cells walls with different enzymes.
  14. Choose the panel of antibacterials that consist of a protein synthesis inhibitor, a nucleic acid synthesis inhibitor, and a cell wall synthesis inhibitor.

    C. Tobramycin, Metronidazole, Vancomycin
  15. Which generation of Cephalosporins is more widely used against gram positive organisms?

    D. 1st
  16. Which generation(s) of Cephalosporins would more likely to be used when treating Pseudomonas spp. infections?

    B. 3rd and 4th
  17. Which antimicrobial agent may be toxic if used inapproproiately?

    B. Gentamicin
  18. Explain the toxic effect of Gentamicin when used inappropriately.
    Gentamicin is an aminoglycoside. This group of antibiotics may cause nephrotoxicity and ototoxicity.
  19. Staph aureus that is resistant to Oxacillin is treated with which glycopeptides?

    B. Vancomycin
  20. Select any of the following that are mechanisms of bacterial resistance.

    a. Alteration of targets' affinity for the drug
    b. Conversion of active drug to inactive drug
    c. Increased drug elimination
    d. Elimination of target
    All are correct
  21. The prevalence of resistance is directly proportional to the amount of antibiotic used.

    a. True
    b. False
    a. True
  22. Give an example of a population that is more at risk of being infected with resistant bacteria.
    Hospital is more likely than community.
  23. When a Nitrocefin Test is performed on an isolate of Haemophilus influenzae, a red color is observed after rubbing the colony on the disk. The technologist should:

    A. Report the organism as resistant to Penicillin/Ampicillin - This test indicates the presence of beta lactamase
  24. The following results were obtained when an Ampicillin microdilution test was performed using E. coli:

    Sterility             Turbid
    Growth              Turbid
    1 ug/mL            Turbid
    2 ug/mL            Turbid
    4 ug/mL            Turbid
    8 ug/mL            Turbid
    16 ug/mL          Turbid
    32 ug/mL          Turbid

    The NCCLS criteria for interpretation for E. coli vs. Ampicillin are as follows:
    S=<8 ug/mL, I=16 ug/mL, R=>32 ug/mL

    Explain how you can evaluate or read these results. What is the MIC of Ampicillin against this strain of E. coli? Is the MIC S, I, or R?
    These results cannot be used because there is growth where there should be sterility.
  25. The following results were obtained when a Ciprofloxacin macrodilution test was performed using S. aureus:

    Sterility       Clear           No growth
    Growth        Turbid
    0.12 ug/mL  Turbid
    0.25 ug/mL  Turbid
    0.5 ug/mL    Clear     Too numerous to count
    1 ug/mL       Clear     Too numerous to count
    2 ug/mL       Clear           No growth
    4 ug/mL       Clear           No growth

    The NCCLS criteria for interpretation for S. aureus vs. Ciprofloxacin are as follows:
    S=<1 ug/mL, I=2 ug/mL, R=>32 ug/mL

    What is the MIC of Ciprofloxacin against this strain of S. aureus? How would you evaluate these results? What is the MBC?
    • The MIC is 0.5 ug/mL, which means this strain of S. aureus is susceptible to Ciprofloxacin.
    • The MBC is 2 ug/mL.
  26. Determining the MBC of a specific agent against the infecting organism when managing the care of the patients. In which situation would a provider more likely need to know the MBC to insure appropriate treatment?

    B. Endocarditis
  27. Explain the use of the E-test strip including how the test is read and interpreted. What is the advantage of using this test?
    • Image Upload 2
    • The E-test strip contains a gradient of an antibiotic and is incubated with an organism on a plate. The strip will cause a tear shaped clearing and the MIC can be read on the strip where the clearing ends. If the tip of the teardrop is hazy, this means that the antibiotic is bacteriostatic and must be read in the middle of the haze.
    • The advantage is that it is easy and gives a true MIC, and much less laborious.
  28. In the disk diffusion method of determining antibiotic susceptibility, the size of the inhibition zone used to indicate susceptibility has been determined:

    A. By correlating the zone size with the MIC - the larger the zone size, the smaller the MIC
  29. Interpreting an antibiotic zone size as being sensitive instead of resistant results in what type of error? How could this error impact patient care?
    By administering a patient with resistant antibiotics, this could lead to toxicity depending on the antibiotic, it could increase the bacteria's resistance, which could be spread in the hospital, and it could hinder the normal flora of patients.
  30. Which of the organisms below are examples of microoganisms that have developed resistance to multiple antimicrobial agents particularly in the hospital setting?

    a. Coagulase negative staph resistant to Penicillin
    b. E. coli that is Hodge Test positive
    c. Enterococcus Resistant to Oxacillin
    d. Staph aureus resistant to Vancomycin
    E. coli that is Hodge Test positive and Staph aureus resistant to Vancomycin
  31. Which drugs are able to reach therapeutic levels in the following anatomic sites? Serum, CSF, and urine respectively.

    B. Clindamycin, Ampicillin, Norfloxacin
  32. Which is a Cephalosporin?

    A. Ceftriaxone
  33. Which is an Aminoglycoside?

    D. Amikacin
  34. Which is an extended spectrum Penicillin?

    A. Ampicillin
  35. Which is a Fluoroquinolone?

    D. Ciprofloxacin
  36. Which is a Glycopeptide?

    D. Vancomycin
  37. Which is a Macrolide?

    C. Erythromycin
  38. Which is an antipseudomonal Penicillin?

    C. Piperacillin
  39. Which is a beta-lactamase stable Penicillin?

    A. Oxacillin
  40. Which is a Tetracycline?

    A. Doxycycline
  41. Which is a Sulfonamide?

    B. SXT
  42. How would a laboratory confirm ESBL resistance?

    C. KB disks showing Cephalosporins becoming more sensitive when a beta-lactamase inhibitor is added
  43. These antibacterial agents have an effect on cell wall synthesis (peptidoglycan).
    • Beta-lactams
    • Glycopeptides
    • Cephalosporins
  44. These antibacterial agents have an effect on protein synthesis (ribosomes).
    • Tetracyclines
    • Macrolides
    • Aminoglycosides
  45. These antibacterial agents have an effect on nucleic acid synthesis (DNA and RNA).
    • Fluoroquinolones
    • Sulfonamides
    • Rifampin
  46. These antibacterial agents have an effect on the cell membrane.
Card Set
Microbiology - Antibiotics
Exam II