The antimicrobial efficacy of household detergents

Environmental awareness in society is changing household laundry habits, which encourage the use of less bleach and lower temperatures during washing machine cycles. In this context, disinfectants added to detergents have become an essential factor in compensating for these new habits and preventing the transmission of bacteria, fungi and viruses in the home, as well as controlling the level of microorganisms that produce bad odors in clothes. .

These products must be evaluated according to standardized methods, but the current European regulation only applies to clinical settings and is restricted to the main wash cycle. Experts from the Biost3 Research Group, led by Antoni Monleón, professor at the Department of Genetics, Microbiology and Statistics at the University of Barcelona (UB), have statistically validated a new method for evaluating the antimicrobial efficacy of detergents and textile additives in domestic environments. The results reveal the validity of the new protocol, which has been presented to the European Committee for Standardization (CEN) to request that it become the European standard.

“It is very difficult to ensure that a product works and is a good disinfectant. We work with microorganisms and the results of the evaluation of the effectiveness can be very variable depending on the method, the washing machine, the temperature, the laundry time, etc. That is why it is very important to publish a standardized protocol (or norm) on a European scale so that manufacturers of textile disinfectants for domestic use can demonstrate the efficacy of their products with a methodology that is much more similar to the real situation in the home”, explains Antoni Monleón, member of the Biostatistics and Bioinformatics Research Group (GRBIO) integrated in the Bioinformatics Barcelona (BIB) platform.

From left to right: Nicolás Ayala, Martín Ríos, Javier Méndez, Toni Monleón-Getino and Joaquín Justel, members of the Biost3 Research Group. (Photo: UB)

The research has been carried out in collaboration with Michelle Cavalleri, a member of the CEN technical committee, and with an international consortium of industrial and testing laboratories formed by AC Marca, Arxada, Eurofins Biolab SRL, Henkel AG & Co KGaA, Hohenstein Laboratories GmbH & Co. KG, Hochschule Niederrhein, FB textile-u Bekleidungs-technick, and Thor Especialidades SA AC Marca researchers Ana Costan and Nuria Piedra have coordinated the development of the standard, the experimental phase and data collection.

Faced with the vacuum in the European Union standards, the consortium organized an international ring trial in order to assess the robustness of a new method specifically designed to test the effectiveness of detergents against microorganisms in a home environment. The seven participating laboratories were equipped with five laboratory-scale devices that simulated domestic washing machines and in which seven parameters were evaluated —among them, the elimination of Escherichia coli or Staphylococcus aureus microorganisms adhered to the fabrics— with different levels of active substance and at various temperatures.

«The evaluation of the disinfectant efficacy in clothing is a complex process that involves many variables and the method must allow controlling aspects such as temperature, contact time, or the mechanical and chemical effect separately, so that the reproducibility is more consistent”, details Antoni Monleón.

This evaluation methodology not only simulates domestic laundry processes, but must be applicable as a standard procedure throughout the sector and, therefore, must be a robust and reproducible method. «Robustness -explains Antoni Monleón- refers to a statistical concept: it is a measure of the ability of the method not to be affected by small but deliberate variations in the experiment, such as the use of washing machines or different temperatures ».

“On the other hand,” continues the researcher, “repeatability means that if an identical method is used with the same procedure in another laboratory, a similar result should be obtained.”

The work of the researchers of the Biost3 Research Group has consisted of validating the method from a statistical point of view and verifying the robustness of the experiments carried out in the different laboratories. With this objective, they have used statistical methods to “detect highly variable values ​​in the experiments, an analysis of strange values ​​for when many variables are taken into account, and graphic methods that allow checking the joint variability of different experimental groups,” explains the researcher.

The results of the investigation have shown that the method was robust against small variations in the experiment, so the repeatability of this, and of the new method, was satisfactory.

In addition, they have created a new library —a program that allows calculations to be carried out very quickly— in the R programming language called Diagnobatch, which can be used in the industrial environment.

The new method also reproduces domestic washing conditions more realistically compared to the current protocol, in which antimicrobial products are tested in industrial washing machines with markedly different characteristics. “Furthermore,” Monleón points out, “previous studies indicate that a laboratory-scale device is not significantly different from a domestic washing machine, but it does have an important advantage in terms of reproducibility and repeatability.”

This new methodology also improves capacity and costs over the current protocol, in which antimicrobial efficacy must be tested separately and a single microorganism assessed per washing machine test. “The new protocol – underlines the researcher – allows up to twenty tests to be carried out simultaneously (depending on the laboratory-scale device) and all the microorganisms are tested in the same test”.

With these promising results, the new methodology has been sent for consultation to the European Committee for Standardization to propose it as a new European standard. “In the medium term,” concludes Monleón, “when the standard is approved by the CEN, all textile disinfectants for the domestic environment that want to register will have to demonstrate their effectiveness by following this protocol, the validity and robustness of which our team has demonstrated.”

The Monleón team presents the technical details of the new protocol in the academic journal PLOS ONE, under the title “International ring trial to validate a new method for testing the antimicrobial efficacy of domestic laundry products”. (Source: UB)