Antibiotic Susceptibility Testing Quiz

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Questions and Answers

What is the main purpose of determining the Minimum Inhibitory Concentration (MIC)?

To check antibiotic potency against viruses

To measure the lowest antibiotic concentration that prevents bacterial growth (correct)

To identify bacterial species

To assess the level of antibiotic resistance genes

Which method uses a polystyrene tray with wells for antibiotic testing?

Disk diffusion test

E-test

Microbroth dilution test (correct)

Macrobroth dilution test

In the disk diffusion test, what indicates that a bacterial isolate is susceptible to the antibiotic?

No growth in the entire agar plate

All bacteria appear resistant

Zone of inhibition around the disk (correct)

Zone of growth around the disk

What turbidity standard is used to standardize the inoculum density for antibiotic susceptibility tests?

0.5 McFarland Signup and view all the answers

Which of the following statements about the E-test is true?

It provides a predefined gradient of antibiotic concentration. Signup and view all the answers

Which statement differentiates macrobroth from microbroth dilution tests?

Macrobroth tests a larger volume of broth than microbroth. Signup and view all the answers

What outcome corresponds to a bacterial isolate with an MIC greater than 4 ug/ml for ciprofloxacin?

Resistant Signup and view all the answers

What is the primary measurement used in the disk diffusion method to interpret antibiotic effectiveness?

Zone of inhibition diameter Signup and view all the answers

What is a limitation of the E-test compared to other methods?

It has a short shelf life and is expensive. Signup and view all the answers

What does intrinsic resistance in bacteria refer to?

Natural resistance present before antibiotic introduction Signup and view all the answers

Which of the following methods is NOT used for antibiotic susceptibility testing?

PCR amplification Signup and view all the answers

How is the minimum inhibitory concentration (MIC) defined?

The highest dilution that inhibits visible growth of a bacterium Signup and view all the answers

What distinguishes macrobroth dilution from microbroth dilution methods?

Macrobroth uses larger volumes for testing Signup and view all the answers

In the disk diffusion method, what does a large zone of inhibition indicate?

Bacterium is susceptible to the antibiotic Signup and view all the answers

What is acquired resistance in bacteria?

Resistance gained after exposure through mutation or gene exchange Signup and view all the answers

What is the minimum bactericidal concentration (MBC)?

Highest dilution that can kill a particular bacterium Signup and view all the answers

Which statement is true regarding susceptibility testing results?

Laboratory results can misrepresent real-world effectiveness Signup and view all the answers

Why is it important to determine antibiotic susceptibility of bacterial isolates?

To ensure the patient receives effective treatment Signup and view all the answers

How can bacteria acquire antibiotic resistance?

Via genetic material exchange or mutations Signup and view all the answers

Study Notes

Antibiotic Susceptibility Testing

Antibiotic Susceptibility Testing is a crucial laboratory method for determining the effectiveness of antibiotics against bacterial isolates.
Quantitative Methods determine the Minimum Inhibitory Concentration (MIC) of an antibiotic, the lowest concentration needed to inhibit bacterial growth.
- Broth Dilution Methods involve serial dilutions of antibiotics in liquid media.
  - 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.
  - 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.
- Agar Dilution Methods are used to determine the MIC on solid media.
  - 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.
Qualitative Methods categorize bacterial isolates as sensitive, intermediate, or resistant to a specific antibiotic.
- 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.
Intrinsic Resistance is when a species is resistant to an antibiotic even before its introduction.
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.