Testing Disinfectant: Introduction, Types, Procedure and Result Interpretation
Testing Disinfectant
Testing disinfectant for working potency is as shown above image.
Introduction of Disinfectant
Disinfection is the process of elimination of most pathogenic organisms excluding bacterial spores on inanimate objects. The efficiency of a disinfectant is tested by measuring the rate of killing effect against a range of microorganisms under specified conditions.
Characteristics of Ideal Disinfectant
- A wide spectrum of activity
- Active at any pH
- Stable
- High penetrating power
- Long shelf life
- Able to destroy microorganisms
- No bad odor within a particular time
- Speedy in action
- Efficacy shouldn’t be lost on reasonable dilution.
- Non-toxic or non-allergic or non-corrosive or non-irritant
- Be active in the presence of organic matter
Factors Influencing the Effectiveness of a Disinfectant
- Nature of the item to be disinfected
- Number and resilience of the contaminants
- Amount of organic material present
- Type and concentration of disinfectant
- Duration and temperature of exposure
Why testing of disinfectants is necessary?
- To know the required effective dilution.
- To know the time taken for the onset of action.
- Periodical monitoring of its activity.
- As disinfectants are known to lose their action on long-standing and in the presence of organic matter their efficacy must be tested periodically
Various types of testing disinfectant
Testing for the potency of disinfectants including-
- Koch method
- Minimum inhibitory concentration (MIC) test,
- Rideal-Walker test,
- Chick-Martin and Garrod test,
- Capacity use dilution test,
- Stability test,
- Test for disinfecting action on surfaces and
- In-use test
Koch method
Spores of Bacillus anthracis are dried on silk thread and are subjected to the action of disinfectants. Later, it is washed and transferred to a solid medium.
Minimum inhibitory concentration (MIC) test
This test measures the lowest concentration of the disinfectant that will inhibit the growth of a known strain of bacterium.
Rideal-Walker test
The test compares the bactericidal activity of the disinfectants with that of phenol. It measures the phenol coefficient of the disinfectants under the standard condition.
Chick-Martin and Garrod test
This assay stimulates natural conditions more closely than the Rideal-Walker test. In this test, a standard amount of organic matter is incorporated in the test mixture. The use of feces has several objectives but Garrod has devised a modification of Chick-Martin test with the use of yeast instead of feces.
Capacity tests
Place each time soiled instrument into a container with disinfectant and add a certain quantity of dirt and bacteria to the solution. The ability to retain activity in the presence of an increasing load is the capacity of the disinfectant. In a capacity test, the disinfectant challenges repeatedly by successive additions of bacterial suspension until its capacity to kill has been exhausted. These tests simulate the practical situations of housekeeping and instrument disinfection. The most common and best capacity test is the Kelsey-Sykes test.
Stability test
Stability test measures the stability and long-term effectiveness of the diluted disinfectant in the clean and dirty medium. It uses to supplement the information obtained from capacity use dilution tests.
Test for disinfecting action on surfaces
This test uses to evaluate new disinfectants, does not take into account the effects of detergents or of the mechanical cleaning process.
In use test
In use, the test determines the number of living bacteria, if any, in a sample of disinfectant from any place or container in which it is being used.
Test requirements for In-use test
- Testing disinfectant
- Nutrient agar
- Incubator
- Pipettes and tips
Test procedure
- Transfer 1 ml of the used disinfectant into 9 ml nutrient broth in a sterile container using a sterile pipette.
- Place 20 µl drops of this mixture onto 10 different areas of each of two nutrient agar plates.
- Incubate on a plate for 3 days and other for 7 days at room temperature.
- Examine the plates and score growth from each drop.
Result Interpretation
Working disinfectant: If growth occurs less than 5 drops out of 10 drops.
Failure of disinfectant: If growth occurs in equal and more than 5 drops out of 10 drops.
Bibliography
- The testing of disinfectants: Gerald Reybrouck, International Biodeterioration and Biodegradation 41 (1998) 269-272
- Joan F.Gardner, Margaret M Peel. 1991. Introduction to sterilization and disinfection control, 2ndedition, Churchill Livingstone
- https://www.microrao.com/micronotes/pg/testing_of_disinfectants.pdf
- https://www.slideshare.net/naik4naik/disinfection-testing-for-disinfection
- https://pubmed.ncbi.nlm.nih.gov/2567307/