18 Questions
What type of antimicrobial drugs are synthesized by chemical procedures in the laboratory?
Synthetics
What is the purpose of Antimicrobial Susceptibility Testing?
To detect antimicrobial resistance
Why is it important to determine the best type of antibmicrobial to be used for a particular microorganism?
Because microorganisms are able to acquire and express resistance to antimicrobial agents
What is the name of the microbiological growth medium commonly used for antibiotic susceptibility testing, specifically disk diffusion tests?
Mueller Hinton Agar
What does MIC stand for?
Minimal Inhibitory Concentration
How is the zone of inhibition determined?
By measuring the diameter of the obvious absence of growth around the antimicrobial disk
What is the primary mechanism of action of penicillin?
Inhibition of cell wall synthesis
Which of the following antimicrobials is effective against gram-positive bacteria?
Vancomycin
What is the term for antimicrobials that are effective against both gram-positive and gram-negative bacteria?
Broad-spectrum
What is the primary mechanism of action of rifampicin?
Inhibition of nucleic acid synthesis
Which of the following is an example of a semisynthetic antimicrobial?
Ampicillin
What is the term for antimicrobials that are derived from microorganisms?
Antibiotic
What is the primary purpose of antimicrobial susceptibility testing?
To determine which antimicrobials will inhibit the growth of the microorganism causing a specific infection
What is the significance of a large zone of inhibition in a Kirby Bauer Chart?
The microorganism is susceptible to the antibiotic
What is the clinical implication of a susceptible result in antimicrobial susceptibility testing?
The antibiotic is likely to be effective in treating the infection
What is the mechanism of action of penicillin?
Inhibiting the synthesis of the bacterial cell wall
What is the significance of an intermediate result in antimicrobial susceptibility testing?
The antibiotic may be effective in treating the infection, but the outcome is uncertain
What is the purpose of comparing the zone size of inhibition to a standard Kirby Bauer Chart?
To determine the susceptibility of a microorganism to an antibiotic
Study Notes
Antimicrobial Drugs
- Synthetics are antimicrobial drugs synthesized by chemical procedures in the laboratory, examples include Sulfonamides and quinolones.
- The use of antimicrobials involves the prescription of a physician, who must ensure the prescribed drug is specific for a particular microorganism causing the disease.
Antimicrobial Susceptibility Testing
- It is a laboratory procedure to detect antimicrobial resistance.
- The most common antimicrobial susceptibility test is the Disk Diffusion (Kirby Bauer Method).
- Sterile disks are impregnated with the Minimal Inhibitory Concentration (MIC) of an antibiotic to determine the sensitivity or resistance of a bacterium to an antimicrobial.
- Mueller Hinton Agar is a microbiological growth medium used for antibiotic susceptibility testing, specifically disk diffusion tests.
Minimal Inhibitory Concentration (MIC)
- MIC refers to the least concentration of an antibiotic that inhibits visible bacterial growth.
- The zone of inhibition is determined by measuring the diameter of the obvious absence of growth around the antimicrobial disk.
Antimicrobial Classification
- Antimicrobials can be classified into three categories: Antibiotics/Antibacterial, Semisynthetic, and Synthetic.
- Antibiotics/Antibacterial are derived from microorganisms, examples include Penicillin and Streptomycin.
- Semisynthetic are chemically derived from antibiotic, example is Ampicillin from Penicillin.
Mechanism of Action
- Inhibition of Cell Wall Synthesis: Penicillin, Ampicillin, Bacitracin, Ristocetin, Vancomycin, Cephalosporin, and Cycloserine.
- Inhibition of Protein Synthesis: Chloramphenicol, Erythromycin, Tetracycline, Streptomycin, Gentamycin, Lincomycin, Clindamycin, and Aminoglycosides.
- Injury to Cell Membrane: Amphotericin B, Polymyxin B, Tyrocidin, and Garamicidin S.
- Inhibition of Nucleic Acid Synthesis: Rifampicin, Quinolones, Sulfonamides, and Trimethoprim.
Kirby Bauer Chart
- The chart is used to compare the zone of inhibition of different antibiotics.
- The zone size of one drug cannot be compared to the zone size of another.
Antimicrobial Susceptibility Testing Procedure
- Plate preparation: 1 medium → 2-8 discs.
- Incubate for 37°C for 18-24 hours.
- Measure the zone of inhibition: large zone = SUSCEPTIBLE, small zone = RESISTANT.
QFR (Quick Facts and Review)
- Purpose of antimicrobial susceptibility test: to determine which antimicrobials will inhibit the growth of the bacteria or fungi causing a specific infection.
- Clinical implications of a Resistant, Intermediate, and Susceptible result:
- Susceptible: high likelihood of therapeutic success.
- Intermediate: uncertain therapeutic effect.
- Resistant: high likelihood of therapeutic failure.
- Mechanism of penicillin: inhibition of cell wall synthesis.
Learn about antimicrobial compounds, antibiotics, and their effects on microorganisms. Understand the differences between narrow-spectrum and broad-spectrum antimicrobials and their effectiveness against various types of microorganisms.
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