MIC 541-Exam 4 -Antimicrobials I-5

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MIC 541-Exam 4 -Antimicrobials I-5
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2013-04-13 10:15:50
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MIC 541 Exam Antimicrobials
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MIC 541-Exam 4 -Antimicrobials I-5
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  1. What is the limit for visible growth?
    • 10,000,000
    • 10^7 CFU/mL
  2. 10^7 CFU/mL represents what?
    Visible growth
  3. Define the Minimum inhibitory concentration (MIC):
    The minimum concentration that inhibits visible growth
  4. What is the term for the minimal concentration to inhibit visible growth?
    Minimum inhibitory concentration (MIC)
  5. What is the definition for significant bactericidal activity?
    Killing of three logs (99.9%) or greater
  6. What is the term for killing of three logs or greater (i.e. 99.9%)
    Significant bacterial activity
  7. Minimum bactericidal concentration is defined as:
    Lowest concentration with significant bactericidal activity
  8. What is the term for the lowest concentration with significant bactericidal activity?
    Minimum bactericidal activity
  9. Frequency of resistant mutants is:
    1 mutant per 10^6 to 10^9 viable bacterial cells
  10. 1 mutant per 10^6 to 10^9 viable bacteria cell represents what statistic?
    Frequency of resistant mutants
  11. What is a breakpoint?
    A determining committee, such as the FDA
  12. Define CLSI:
    Clinical and Laboratory Standards Institute
  13. Define EUCAST:
    European Committee on Antimicrobial Susceptibility Testing
  14. What categories of test results for susceptibility exist?
    • Susceptible
    • Intermediate
    • Resistant
  15. Give examples of determining committees or Breakpoints:
    • FDA
    • CLSI
    • EUCAST
  16. The FDA, EUCAST and CLSI all fall under what greater category?
    Breakpoints or Determining committees
  17. How do we detect resistance?
    Susceptibility tests
  18. Good susceptibility is a guarantee of success with a given antimicrobial agent (T/F)?
    False
  19. Susceptibility tests are not adequate (T/F)?
    True, we need to optimize detection of resistance
  20. Therapeutic success depends on what other factors other than susceptibility?
    • Penetration of drug at infection site
    • Immune status
    • Need for surgery
  21. ___________ is dependent on Immune status, penetration of drug at infection site and need for surgery?
    Therapeutic success
  22. Disk diffusion can be described as what type of measure of susceptibility?
    Qualitative
  23. Name a qualitative test for susceptibility:
    Disk diffusion
  24. Potency of drugs can be compared using qualitative means (T/F)?
    False
  25. What was discussed in class as not accomplishable via Qualitative testing?
    Comparison of drug potency
  26. What examples were given in class for Qualitative tests?
    • Measure of susceptibility
    • Comparison of drugs
    • Macrobroth dilution
    • Microbroth Dilution
    • Agar dilution
    • E-test
  27. E-test, measure of susceptibility, drug comparisons, macrobroth dilution, microbroth dilution and agar test are all what general type test?
    Quantitative
  28. Describe the process of creating a Macrobroth dilution:
    • 1-3 mL Volumes of broth
    • Dilute drug in 2 fold dilution to get to 0.06 ug/mL of the drug
    • Inoculate with 5E5 CFU/mL
    • Incubate for 18-24 hours
  29. What is the inherent Error of the susceptibility test?
    • Inherent 2 fold error of MIC test
    • i.e. 2ug/ml can be 1-4 ug/ml
  30. What is the Inoculum effect?
    • The inoculum in the MIC test is much lower than in a real infection
    • Does not account for pathogens production of antibiotic inactivating enzymes
  31. What technical difficulties may arise in susceptibility tests?
    • Fuzzy or trailing endpoints
    • Difficult to interpret
  32. What limitations are inherent in the MIC test?
    • Inherent error = inherent 2 fold error in dilutions
    • Inoculum effect = inoculation in MIC test is usually much lower than in vivo/does not account for pathogen production of antibiotic inactivating enzyme
    • Technical difficulties= diff. to interpret results
  33. Macrobroth dilution is what general type of assay?
    Quantitative
  34. What are the advantages of a Macrobroth dilution?
    • Quantitative
    • Most conservative (gives the highest MIC)
    • Gold standard
    • Can measure Minimum Bactericidal concentration
  35. What test is quantitative, conservative (giving the highest MICs), able to measure MBC and considered the Gold standard for susceptibility assays?
    Macrobroth Dilution
  36. What disadvantages are there for Macrobroth Dilution?
    • Labor intensive
    • Inoculums below 10^6 = missed mutants
  37. What test is unable to detect inoculums below 1066 and is considered labor intensive?
    Macrobroth Dilution
  38. What is the dilution volume for Microbroth dilution?
    0.1mL
  39. Describe the Microbroth Dilution method:
    • 0.1mL volumes
    • Dilute 2 fold to reach 0.06ug/mL
    • 50,000 CFU/mL inoculum
    • Incubate 18-24 hours
  40. Why is Microbroth considered less accurate than a Macrobroth?
    The smaller the sample size the less accurate the results
  41. Why is a Macrobroth Dilution considered more accurate than a Microborth?
    Larger sample size equates to more accurate results
  42. When accuracy is the most important component of your testing, what susceptibility assay would you choose, Microbroth or Macrobroth?
    Macrobroth
  43. Describe an agar dilution susceptibility test:
    Spread plating of agar is performed on plates of varying concentration
  44. What are the benefits of using an Agar dilution susceptibility test?
    • Quantitative
    • 32 strains per drug plate
    • Easier than macrobroth
  45. What susceptibility test is Quantitative, easier than macroborth and allows for 32 strains to be plated per plate?
    Agar Dilution
  46. What disadvantages exist for the Agar dilution susceptibility test?
    • Does not yield a minimum bactericidal concentration
    • MICs are lower than macrobroth
    • Lower inoculum
  47. What test does not yield MBCs, has MICs that are lower than macrobroth and a low inoculum?
    Agar Dilution
  48. An E-test is similar to what other tests?
    Agar dilution and disk diffusion
  49. What susceptibility test is similar to an agar dilution and disk diffusion?
    E-test
  50. Describe the method for an E-test:
    • Spread a lawn of bacteria
    • Apply E-test strip
    • Incubate for 18-24 hours
  51. What test requires a lawn of bacteria, an antibiotic gradient strip and an incubation period of 18-24 hours?
    E-test
  52. Describe the characteristics of an E-test strip:
    Plastic strip coated with antibiotic gradient
  53. What is the name for a strip coated with an antibiotic gradient?
    E-test Strip
  54. In the E-test what happens to the antibiotic during incubation?
    Diffuses into the agar at rate dependent on the concentration
  55. Describe how you read an E-test:
    The point of the E-test strip that aligns with the lowest concentration point where bactericidal activity can be detected= MIC
  56. What are the advantages of the E-test:
    • Quantitative
    • 6 drugs can be tested concurrently
    • Easy
  57. What susceptibility test allows for 6 drugs to be tested concurrently, is quantitative and easy to perform?
    E-test
  58. What are the disadvantages of the E-test?
    • Does not yield MBCs
    • Costly
    • Results are difficult to interpret
  59. What susceptibility test has results that are difficult to interpret, does not produce MBC data and is costly?
    E-test
  60. Describe the method for Disk Diffusion:
    • Spread a lawn of bacteria
    • Apply antibacterial impregnanted disk
    • Incubate 18-24 hours
    • What test requires a lawn to be spread, antibacterial impregnated disks to be layed on the lawn and an incubation period of 18-24 hours?
    • Disk Diffusion
  61. How is a disk diffusion test interpreted?
    By measuring the zone of inhibition
  62. What susceptibility test is interpreted by measuring the zone of inhibition?
    Disk Diffusion
  63. What variables control the zone of inhibition in the Disk diffusion test?
    • Temperature
    • Concentration of Drug disk
    • Inoculum size
    • Susceptibility of test organism
  64. Temperature, Conc. Of drug, inoculum size and susceptibility of test organism are all variable factors for what susceptibility test?
    Disk Diffusion
  65. What are the advantages of disk diffusion?
    • Fast and easy to perform
    • Inexpensive
    • Many drugs can be tested concurrently
    • Drug interactions may be detected
    • New drugs are usually available for this test type
  66. What is the disadvantage of the disk diffusion assay?
    You cannot tell HOW sensitive the organism is from the zone size
  67. What I easy, fast, inexpensive, able to determine the susceptibility of many drugs concurrently, can detect drug interactions and has new drugs available for testing?
    Disk Diffusion
  68. What are the advantages of automated susceptibility tests?
    • Rapid, accurate and cheap
    • Reduce workload
    • Very specific computer analyzed results
  69. What are the disadvantages for automated susceptibility tests?
    Algorithms may be inaccurate for certain organisms, drugs or inoculum concentrations
  70. A negative result for a Molecular detection of resistance genes test means what?
    Does not mean the organism is susceptible
  71. What are the shortcomings of Molecular detection of resistance genes?
    Genes that are too diverse may not be detected
  72. What are the positive aspects of Molecular detection of resistance genes?
    • Potential for:
    • Rapid results
    • Accurate results
    • Highly specific results
  73. What issue require resolution prior to routine use of Molecular detection of resistance gene testing?
    • Cost
    • Convenience
    • Preventative measures for over and understating resistance
    • Needs methods for detecting new resistance genes
  74. Phenotypic tests for resistance have a broader scope than Molecular detection of resistance genes test (T/F)?
    True
  75. What is the point of Irreversibility?
    The point beyond which treatment will have no impact on an outcome of an infection
  76. What is the term for the point beyond which most appropriate treatment will have no impact on the outcome?
    Point of irreversibility
  77. What has been well studied in terms of the point of irreversibility?
    • Pneumonia (most well studied)
    • Sepsis
    • Meningitis
    • Neutropenia
  78. Pneumonia, Sepsis, Meningitis and Neutropenia have all been studied (Pneumonia more so than the others) in terms of what characteristic?
    Point of irreversibility
  79. What differences in Rapid vs microdilution susceptibility methods were discovered by the Doern study?
    • The mortality rate was lower for those receiving a rapid susceptibility method
    • Fewer procedures were used on patients receiving rapid methods
    • Faster witch from empiric Rx
  80. Why is early antibiotic administration more robust?
    Attacks the pathophysiological process
  81. What is the social impact of using Rapid susceptibility methocs?
    • Reduction of therapy cost
    • 2.4 million Saved/year
    • Early isolation of patient=less unnecessary spread
  82. How can we diminish the development of resistance?
    Diminish drug use

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