Susceptibility Testing
Susceptibility testing is a laboratory method used to evaluate the effectiveness of antimicrobial agents against specific microorganisms. The process determines whether a microorganism, such as bacteria or fungi, is susceptible, intermediate, or resistant to a particular antimicrobial. This testing is essential in clinical microbiology, guiding the selection of appropriate therapeutic agents for the treatment of infections and in monitoring resistance patterns in pathogens.
Content
- Purpose of Susceptibility Testing:
- Determines the efficacy of antibiotics, antifungals, or antivirals against a given pathogen.
- Supports clinicians in selecting effective antimicrobial therapy.
- Tracks the emergence and spread of antimicrobial resistance.
- Methodologies:
- Disk Diffusion (Kirby-Bauer Method):
- Involves placing antibiotic-impregnated disks on an agar plate inoculated with the test organism.
- Zones of inhibition (clear areas around the disks) indicate the organism’s susceptibility.
- Disk Diffusion (Kirby-Bauer Method):
- Broth Dilution (MIC Determination):
- Involves serially diluting the antimicrobial agent in liquid media and inoculating with the test organism.
- The minimum inhibitory concentration (MIC) is the lowest concentration that inhibits visible growth.
- E-Test (Gradient Diffusion):
- Combines features of disk diffusion and MIC determination.
- Uses a strip impregnated with a gradient of antimicrobial concentration.
- Broth Dilution (MIC Determination):
- Applications:
- Clinical Decision-Making:
- Assists in the selection of targeted antimicrobial therapy, improving patient outcomes.
- Reduces the use of broad-spectrum antibiotics, limiting collateral damage to the microbiota.
- Antimicrobial Stewardship Programs:
- Enables institutions to monitor and optimize antimicrobial use.
- Helps in reducing the development of resistance.
- Epidemiological Surveillance:
- Monitors trends in antimicrobial resistance globally and locally.
- Supports the development of policies to control the spread of resistant strains.
- Clinical Decision-Making:
Susceptibility testing is a cornerstone of infectious disease management, enabling precise and effective treatment of infections. Advances in both phenotypic and genotypic methods continue to improve the speed and accuracy of susceptibility testing.
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