Microbiology || Laboratory Diagnosis: Antibiotic Sensitivity Testing || Nursing Alert ||

 

Laboratory Diagnosis: Antibiotic Sensitivity Testing

Antibiotic sensitivity testing (AST) is a laboratory procedure used to determine the susceptibility of bacteria to various antibiotics. It helps guide clinicians in selecting the most effective antimicrobial therapy for patients with bacterial infections. This testing is particularly critical in managing infections caused by multidrug-resistant organisms and in optimizing treatment to prevent antimicrobial resistance.



Antibiotic Sensitivity Testing: Methods

1. Disc Diffusion Method (Kirby-Bauer Test):

  • Involves placing antibiotic-impregnated discs on an agar plate inoculated with the bacteria of interest.
  • After incubation, the zones of inhibition (areas where bacteria cannot grow around the discs) are measured.
  • Results are interpreted as Sensitive (S), Intermediate (I), or Resistant (R).

2. Broth Dilution Method:

  • Includes both macro and microdilution techniques.
  • Determines the Minimum Inhibitory Concentration (MIC) — the lowest concentration of an antibiotic that inhibits visible bacterial growth.
  • Provides quantitative results.

3. E-test (Epsilometer Test):

  • A gradient strip with a concentration range of an antibiotic is placed on an agar plate inoculated with bacteria.
  • MIC is read directly from the point of intersection of the inhibition zone with the strip.

4. Automated Systems:

  • Systems like VITEK, BACTEC, or Phoenix automate the process of determining bacterial identification and antibiotic susceptibility.
  • Faster and more accurate, often preferred in clinical settings.

5. Genotypic Methods:

  • Detects genes responsible for antibiotic resistance, e.g., PCR-based tests.
  • Useful for organisms with known resistance mechanisms.

Nursing Responsibilities in Antibiotic Sensitivity Testing

Pre-test Responsibilities:

  1. Sample Collection and Handling:

    • Collect specimens (blood, urine, wound swabs, sputum) using aseptic techniques to avoid contamination.
    • Ensure the sample is adequate in quantity and properly labeled.
    • Transport the sample promptly to the laboratory, maintaining the required temperature and conditions.

  2. Patient Preparation:

    • Educate the patient about the test, including its purpose and process.
    • Ensure fasting or other specific instructions are followed if required.

  3. Documentation:

    • Accurately document patient details, clinical history, and suspected infection site on the lab requisition form.

During the Test:

  1. Coordination with Laboratory Staff:

    • Ensure timely communication between nursing staff and the laboratory for processing urgent or critical samples.

  2. Ensuring Proper Storage:

    • Store collected samples temporarily in appropriate conditions if immediate transport is not possible.

Post-test Responsibilities:

  1. Receiving and Reporting Results:

    • Retrieve and review the AST report once available.
    • Inform the treating physician about the results promptly.

  2. Implementation of Antibiotic Therapy:

    • Administer prescribed antibiotics as per the sensitivity report.
    • Monitor the patient for therapeutic efficacy and adverse reactions to antibiotics.

  3. Patient Education:

    • Educate the patient and their family about the importance of adhering to the prescribed antibiotic regimen.
    • Discuss measures to prevent the misuse of antibiotics, such as avoiding self-medication.

  4. Monitoring and Follow-Up:

    • Monitor the patient for clinical improvement and report any signs of treatment failure.
    • Coordinate follow-up culture tests if required.

Nursing Role in Infection Control:



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