Disinfectant claims – where do they come from, and can we trust them?
Disinfectants are chemical substances intended to destroy, control, or prevent the growth of pathogenic microorganisms. Different active ingredients, concentrations, and administration route can affect the biocidal performance. With the increasing awareness on environmental contamination, the spotlight is firmly fixed on the disinfectants’ efficacies, and whether their claims are substantiated by thorough testing and evaluation.
There are numerous standardized methodologies to evaluate disinfectants, including screening tests, challenge tests, and even field trial tests. Among them, European Standard EN 1276, a quantitative suspension test, is one of the most commonly used standard to evaluate chemical disinfectants’ bactericidal activity intended for use in food, industrial, domestic, and institutional areas.
EN 1276 test condition and parameters
The EN 1276 standard stipulates a range of parameters for the test, which includes bacteria type, contact time, test temperature and interfering substances.
1. Mandatory test microorganism
Bacteria species can be broadly separated into two main categories based on the structure of bacterial cell wall, namely gram-positive bacteria and gram-negative bacteria. The cell wall serves as a protective membrane to the bacteria, allowing bacteria to survive under extreme temperature and pH. The EN 1276 standard provides a mandatory list of microorganisms which are scientifically representative to cover both categories of bacteria.
2. Contact time
This parameter refers to the duration of action by the disinfectant. In general, a longer contact time gives a higher disinfection efficacy. For the EN 1276 test to be relatable to actual use scenario, it is important to define an appropriate contact time. For example, when testing a hand disinfectant, a 5-minute contact time is considered unrealistic. A more appropriate contact time (i.e., 30s or 60s) should be considered.
3. Test temperature
Temperature has a direct effect on bacteria survivability and is a controlled parameter in the EN 1276 test standard. Typically, lower temperatures favor bacteria survival and can mask the disinfectant’s bactericidal efficacy in actual use conditions. Therefore, EN 1276 should be conducted at a temperature that is representative to the intended disinfectant usage.
4. Interfering substance
When disinfectants are applied in real life, interfering substances such as food debris, oils, dust, etc. may be present and can potentially affect the bactericidal performance. Artificial substances can be added to the EN 1276 test to evaluate disinfectants’ efficacy under “dirty” conditions. EN 1276 performed “under dirty conditions” is mandatory for products with combined cleaning & disinfection functions. In contrast, EN 1276 performed without the addition of interfering substance (“under clean conditions”) is designed for disinfection products that require additional prior physical cleaning.
In brief, the disinfectant (in ready-to-use format), microorganism and interfering substances are mixed in an 8:1:1 ratio. The mixture is allowed to interact under the pre-determined test temperature and contact time. The experiment is then quenched by the addition of a neutralizing solution, and any surviving microorganism is allowed to proliferate for 2 days. The disinfection efficacy is calculated by comparing the bacteria count from test solution to the original cultural solution. To pass the test of EN 1276, the product must be able to demonstrate a 5-log reduction (>99.999% killing rate) against the listed microorganisms.
One of the major limitations of such standard test is its poor representation of actual use conditions. For example, the methodology fails to include the effects of different administration routes (e.g. spray, wipe, mist), target surface (porous (e.g. fabrics) vs non-porous (i.e. plastic / metal)), and actual environmental conditions, etc. In addition, when using disinfectants with autonomous bio-decontamination systems such as disinfection robots, a realistic simulation test methodology should be included to fully understand the effectiveness of the combined approach.
All standardized methodologies (including EN 1276 suspension test) are designed based on sound scientific principles. EN 1276 suspension test is a highly reproducible and simple methodology, and serves as an important foundation to evaluate the bactericidal efficacy of the majority of disinfectants currently on the market today. However, it is also important for end-users to understand these experimental results are produced in laboratory environment and are often not completely reflective of actual use environment. Be sure to follow our insight pieces, as we will continue to discuss various tests and industry standards used to further evaluate disinfectant efficacies.