Fungal contamination is a major risk whether in healthcare facilities or in food production industries. Among the various workable solutions to control fungal pathogens in the environment is the use of disinfectants. The effectiveness of disinfectants to reduce or destroy fungal spores is tested using the AOAC 955.17 test, which is commonly known as the fungicidal activity test. This article describes the science of antifungal tests and, in particular, the AOAC dilution methods to assist in appreciating not only the application but also the relevance of these tests to industry.
Understanding Fungal Contamination
To understand the reason behind the constitution of a procedure for testing the effectiveness of a given disinfectant against fungal spores, it is of utmost necessity to get an idea of the overall problem and the issues related to contamination by fungi. Fungi are so ubiquitous within the environment that they can cause infections, food spoilage, and surface fouling. Common pathogenic fungi comprise Trichophyton mentagrophytes, Aspergillus niger, and Candida albicans. All of these fungi are spore formers, and under almost any environment, the spores can germinate.
The AOAC 955.17 Fungicidal Activity Test
Purpose and Importance
The AOAC method 955.17 is designed to demonstrate the fungicidal activity of disinfectants against the fungus Trichophyton mentagrophytes. This test is significant as it demonstrates whether the fungicidal action exerted by a disinfectant will be effective on different surfaces against fungal spores. This method assists manufacturers in ensuring that their products meet regulatory requirements and consistently provide effective protection from contamination by fungal pathogens.
Testing Protocol
The fungicidal test method AOAC 955.17 involves several principal steps:
- Culturing: Culturing of a standard fungus strain, such as Trichophyton mentagrophytes, is carried out to get the mycelium growth which may provide spores. The mycelium is resuspended in a solution to produce a spore suspension.
- Dilution: The test disinfectant is subjected to serial dilutions. This is necessary for determining the highest dilution showing fungicidal activity.
- Contact: Dilutions of the test substance are inoculated with a known aliquot of the fungal spore suspension. The test mixtures are maintained in a recirculating water bath to ensure a constant temperature. Aliquots from each test mixture are transferred to the neutralizer growth medium after the required contact period.
- Incubation: After the contact period has lapsed, the neutralized aliquots are incubated for approximately 10 days at the appropriate temperature to determine fungal growth.
- Evaluation: After incubation, the tubes are subcultured, and the results are assessed to determine the highest dilution that shows no fungal growth. This result indicates the highest admissible dilution for disinfecting a surface contaminated with the fungus during the given contact time.
Key Factors Influencing the Test
Several factors can influence the results of the AOAC 955.17 test, including:
- Contact Time: Increasing the exposure time of the test organisms to the disinfectant will give a significant increase in the activity of the disinfectant towards improved activity.
- Temperature: The test should be carried out under recommended temperature conditions. Instabilities in the test temperature influence the growth of the test organisms and, therefore, test disinfectant performance.
- Neutralization: After the contact period lapses, the test substance must be inactivated. If this is not done, the neutralization may occur during the outgrowth phase of the test, which will disturb the test result.
Advantages of Using the AOAC 955.17 Method
- Standardization: AOAC 955.17 uses a standardized procedure that produces uniform and reproducible results within and in between the laboratory and across studies.
- Regulatory Statement Adherence: The use of an acknowledged method like AOAC 955.17 results in compliance with the requirements of regulatory authorities and industry standard requirements.
- Flexibility within the Test: The ability to study different disinfectants against different strains of fungi provides this kind of flexibility, making the test convenient for different working areas and industries.
- Reliability: The test is strictly performed under a fixed protocol, which makes it possible to correctly establish the fungicidal activity of the tested disinfectant and ensures its activity.
Use of AOAC Dilution Methods
The AOAC Dilution methods (AOAC 955.14, AOAC 955.15, AOAC 955.17, AOAC 964.02) are applied in numerous application areas for generating valid and reliable results in the analysis of disinfectants.
Healthcare Settings: The risk for fungal contamination within a healthcare environment may lead to healthcare-associated infections (HAIs). The standards are used in testing the fungicidal properties of hospital-grade disinfectants to ensure that those disinfectants can kill fungal spores from surfaces, equipment, and other areas in the healthcare facility.
Food Industry: The food industry is fraught with risk if fungal contamination leads to spoilage and foodborne illnesses. In this situation, the method is used in testing the fungicidal activity of the disinfectants for use within processing plants, storage bins, and packaging lines to ensure the safety of the products and extend their shelf life.
Pharmaceutical Industry: Any pharmaceutical environment is directly associated with hygienic measures necessary for keeping the sterility of the products and avoiding any potential cross-contamination between drugs and medical devices. The AOAC method is applied to assess the effectiveness of relevant disinfectants against fungal spores for use in aseptic cleanroom disinfection and other controlled environments.
Challenges and Issues
Strain Variability: One of the challenges associated with the fungicidal test is the varying resistances between different fungal strains. The chosen test strains have to be representative of realistic scenarios. Furthermore, the test procedure might need to be updated regularly with respect to newly discovered fungal pathogens.
Optimizing the Contact Times: One challenge is the contact time optimization. Though extending contact time normally increases fungicidal activity, other practical aspects must be considered, such as workflow disruption and safety considerations. Contact times must be designed for effectiveness and practicality in routine disinfection.
Environmental Parameters: The potential of the disinfectant can be affected by environmental factors. Controlled environmental conditions, both for testing and real application, must be maintained. Additionally, the activity of the disinfectant is greatly affected by the presence of organic materials; therefore, the surface or article should be cleaned and wiped before disinfection.
How can MIS help?
At Microbe Investigations Switzerland, we specialize in fungal testing using the AOAC Dilution Methods, providing precise and reliable insights into fungal contamination and the efficacy of fungicidal products. Our expert team of microbiologists is equipped with the latest technology and methodologies to ensure that your products meet the stringent standards required for safety and effectiveness. Trust MIS to deliver comprehensive fungal testing services that are both thorough and scientifically robust.
To learn more about how our fungal testing capabilities can benefit your product development or to schedule an in-depth consultation, please contact our experts today.
