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Questions and Answers
What is the main purpose of determining the Minimum Inhibitory Concentration (MIC)?
Which method uses a polystyrene tray with wells for antibiotic testing?
In the disk diffusion test, what indicates that a bacterial isolate is susceptible to the antibiotic?
What turbidity standard is used to standardize the inoculum density for antibiotic susceptibility tests?
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Which of the following statements about the E-test is true?
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Which statement differentiates macrobroth from microbroth dilution tests?
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What outcome corresponds to a bacterial isolate with an MIC greater than 4 ug/ml for ciprofloxacin?
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What is the primary measurement used in the disk diffusion method to interpret antibiotic effectiveness?
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What is a limitation of the E-test compared to other methods?
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What does intrinsic resistance in bacteria refer to?
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Which of the following methods is NOT used for antibiotic susceptibility testing?
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How is the minimum inhibitory concentration (MIC) defined?
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What distinguishes macrobroth dilution from microbroth dilution methods?
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In the disk diffusion method, what does a large zone of inhibition indicate?
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What is acquired resistance in bacteria?
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What is the minimum bactericidal concentration (MBC)?
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Which statement is true regarding susceptibility testing results?
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Why is it important to determine antibiotic susceptibility of bacterial isolates?
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How can bacteria acquire antibiotic resistance?
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Study Notes
Antibiotic Susceptibility Testing
- Antibiotic Susceptibility Testing is a crucial laboratory method for determining the effectiveness of antibiotics against bacterial isolates.
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Quantitative Methods determine the Minimum Inhibitory Concentration (MIC) of an antibiotic, the lowest concentration needed to inhibit bacterial growth.
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Broth Dilution Methods involve serial dilutions of antibiotics in liquid media.
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Macrobroth Dilution MIC Tests use test tubes with a larger volume of broth and are used to create a serial two-fold dilution of antibiotic.
- The inoculum density is standardized with a 0.5 McFarland turbidity standard to have a final inoculum of 5 x 10^5 cfu/ml.
- The lowest concentration of antibiotic that completely inhibits visible growth is recorded as the MIC.
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Microbroth Dilution MIC Tests utilize polystyrene trays with wells containing a smaller volume of broth and serial dilutions of antibiotics.
- The bacterial inoculum is standardized according to the McFarland standard and inoculated into each well.
- The MIC is determined by examining the wells for visible growth.
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Macrobroth Dilution MIC Tests use test tubes with a larger volume of broth and are used to create a serial two-fold dilution of antibiotic.
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Agar Dilution Methods are used to determine the MIC on solid media.
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E-test uses strips with a predefined gradient of antibiotics (one strip per antibiotic) for easy use and broad coverage.
- The E-test reads resistant, intermediate, and susceptible based on the minimum inhibitory concentration determined.
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E-test uses strips with a predefined gradient of antibiotics (one strip per antibiotic) for easy use and broad coverage.
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Broth Dilution Methods involve serial dilutions of antibiotics in liquid media.
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Qualitative Methods categorize bacterial isolates as sensitive, intermediate, or resistant to a specific antibiotic.
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Disk Diffusion Test involves placing paper discs with specific antibiotic concentrations on an agar plate inoculated with the bacterial isolate.
- Susceptibility is determined by the zone of inhibition (no growth) around the disc.
- Larger zones indicate higher sensitivity.
- The diameter of the zone is measured and compared to standardized charts for interpretation.
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Disk Diffusion Test involves placing paper discs with specific antibiotic concentrations on an agar plate inoculated with the bacterial isolate.
- Intrinsic Resistance is when a species is resistant to an antibiotic even before its introduction.
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Acquired Resistance is when a species was previously susceptible to an antibiotic but later developed resistance.
- Mutation changes the bacterial DNA, leading to resistance.
- Horizontal Gene Transfer involves the exchange of genetic material between bacteria, allowing for the spread of resistance.
- Factors Affecting Antibacterial Activity in vivo may differ from laboratory results, limiting the translation of in vitro susceptibility results to clinical outcomes.
Minimum Inhibitory Concentration (MIC)
- MIC represents the highest dilution of an antibiotic that inhibits the growth of a bacterial isolate.
- Minimum Bactericidal Concentration (MBC) is the highest dilution of a drug that kills a specific bacterium.
Bacterial Resistance
- Acquired Resistance poses a significant challenge in treating bacterial infections.
- Multi-drug Resistance (resistance to multiple antibiotics) is a serious concern.
- Susceptibility Testing is essential for guiding antibiotic therapy to ensure effective treatment.
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Description
Test your knowledge on antibiotic susceptibility testing methodologies, including quantitative methods for determining Minimum Inhibitory Concentration (MIC). This quiz covers various techniques such as broth dilution methods and their applications in microbiology. Challenge yourself and learn more about the crucial laboratory tests used to combat bacterial infections.
