Standard Operating Procedure (SOP)

1. Purpose

To establish a standardized procedure for testing the efficacy of disinfectants to ensure they meet required standards for microbial control and surface sanitation.

2. Scope

This SOP applies to all disinfectant products and formulations being tested for efficacy against specific microorganisms in controlled environments (e.g., healthcare facilities, laboratories, or manufacturing plants).

3. Responsibilities

• Microbiologist/QA Officer: Oversee and perform testing, record data, and analyze results.

• Lab Technician: Prepare test materials, handle microbial cultures, and perform the test under guidance.

• Disinfectant Manufacturer (if applicable): Provide necessary data about the disinfectant’s active ingredients, usage guidelines, and expected efficacy.

4. Definitions

• Disinfectant: A chemical agent used to reduce or eliminate harmful microorganisms on surfaces.

• Efficacy: The ability of a disinfectant to kill or inactivate microorganisms (bacteria, viruses, fungi, etc.) within specified time frames.

• Test Microorganism: The specific bacteria, viruses, or fungi used in testing (e.g., Staphylococcus aureus, Escherichia coli, etc.).

• Contact Time: The required time the disinfectant must remain in contact with the surface to be effective.

5. Procedure

5.1 Preparation

1. Selection of Test Organism(s): Choose the microorganisms that the disinfectant is expected to target. Common test organisms include Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli, Influenza virus, etc.

2. Prepare Test Samples:

   • Prepare microbial cultures according to the standard protocols.

   • Create a suspension of microorganisms with a known concentration.

3. Prepare Disinfectant Solution:

   • Dilute the disinfectant as per manufacturer instructions.

   • Ensure the correct concentration for the efficacy test.

   • Label the disinfectant container with dilution details.

5.2 Test Setup

1. Surface Preparation:

   • Use non-porous, uniform surfaces (e.g., stainless steel, glass, or plastic) for testing.

   • Clean the surfaces to remove any dirt or debris that might interfere with the disinfectant’s activity.

2. Inoculation:

   • Apply a standardized inoculum of the test microorganism to the surface.

   • Allow the inoculum to dry for the designated time before applying the disinfectant.

3. Application of Disinfectant:

   • Apply the disinfectant solution to the inoculated surface according to the procedure’s required contact time.

   • Ensure even coverage of the disinfectant on the surface.

5.3 Incubation and Neutralization

1. Contact Time:

   • Allow the disinfectant to remain on the surface for the specified contact time (as per the product’s efficacy claims).

2. Neutralization: After the contact time has passed, neutralize the disinfectant using an appropriate neutralizing agent to stop the disinfectant’s action and prevent further killing.

   • For example, use a neutralizing broth or solution.

5.4 Recovery and Enumeration

1. Recovery of Organisms:

   • After neutralization, rinse the surface and collect the rinse fluid.

   • Plate the rinse fluid onto selective agar plates to recover any surviving microorganisms.

2. Incubation:

   • Incubate the plates at the appropriate temperature for the recommended time to allow microbial growth.

   • For bacterial tests, typically 24–48 hours of incubation is required.

5.5 Data Analysis and Reporting

1. Colony Counting: After incubation, count the number of colonies that have grown.

2. Calculate Efficacy: The efficacy is determined by comparing the number of colonies on the treated surface with those on a control (untreated) surface.

   • Efficacy = [(Initial Count – Final Count) / Initial Count] x 100%

   • Efficacy results should be expressed as a percentage reduction of microorganisms.

3. Interpret Results: If the efficacy is below the acceptable threshold (usually 99.9% or 3-log reduction for surface disinfectants), the disinfectant is considered ineffective for that microorganism.

5.6 Documentation and Records

• Record the following details in the test report:

  • Date and time of testing

  • Test microorganism(s) and their concentration

  • Disinfectant product and concentration used

  • Contact time

  • Recovery method and results

  • Control (untreated) and treated surface results

  • Any deviations or anomalies observed during testing

• Save results in a secure and organized manner for future reference or regulatory compliance.

6. Acceptance Criteria

• The disinfectant should demonstrate a minimum reduction of 99.9% (3-log) in microbial population.

• If the efficacy is below the threshold, further investigations or formulation changes may be required.

7. Safety and Compliance

• Follow all laboratory safety protocols, including the use of PPE (e.g., gloves, lab coats, face shields).

• Properly handle and dispose of all microbial cultures and contaminated materials according to biosafety guidelines.

• Ensure that all disinfectants and chemicals are handled in accordance with their respective Safety Data Sheets (SDS).

8. Annexures

• Microbial Testing Data Sheets

• Disinfectant Efficacy Test Report Template

• Disinfectant Handling and Dilution Guide

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