Household laundry processes have changed a great deal in recent times following the development of synthetic textiles and due to the idea of sustainability. The use of bleach-containing detergents has decreased, along with the quantity of water used and the average washing temperature. This has a huge effect on the washing results, i.e. the removal of dirt and odours, as well as on hygiene. The aforementioned developments are believed to make the destruction of harmful microbes during the washing process less efficient. It is further expected that the presence of a broad range of pathogenic microbes will also lead to a higher risk to human health. The washing machine industry is developing numerous strategies to prevent or remove biofilm in washing machines. However, suitable standards and test methods to assess the hygienic performance of detergents in situ and their effect on biofilm formation are still lacking. Empa Testmaterials is seeking to redress this situation. The St. Gallen (Switzerland) based company develops test methods to assess the hygienic effect of washing programmes, detergent raw materials, wash cycles and washing machine cleaners.

"We use washing machines every day, but not all of them are being used every day," said Caroline Amberg, project manager microbiology at Empa Testmaterials. Amberg and her team focus on the development of a reproducible and storable microbial biofilm for a test method that allows the quantification of biofilm removal. "We have observed huge variations in terms of cells and biofilm matrix (exopolymeric substance = EPS) between the time that the first microbial cells adhere to the surfaces and the final biofilm is created," said the biologist explaining the challenge the researchers face. Washing clothes in a washing machine or dishes in a dishwasher is a highly complex process, where mechanics, chemistry and biology act together. "It is impossible to simulate this process with a suspension test, as is the case when testing disinfectants," said Daniel Fäh, managing director of the company which is a spin-off of the EMPA - Swiss Federal Laboratories for Materials Science and Technology.

The foul-smelling, slimy films can contain pathogens and affect human health, for example in cases where people have medical implants, the pathogens can lead to severe inflammation. "However, no founded studies to correlate disease outbreak with bad washing hygiene are available," said Caroline Amberg. The St. Gallen-based company has recently developed a test system that can be used in-house by washing machine and detergent manufacturers. "The use of risk class 1 test microorganisms and a simple protocol make it possible to carry out the test without having to use a microbiological laboratory," added the biologist.

The company has at its disposal 11 washing machines from the USA, Asia and Europe to analyse biofilms that occur in washing machines. "Different climate, water quality and other washing habits play a major role in the development of biofilms. For example, we found that the American test devices were covered with larger amounts of mould than the other washing machines tested," said Caroline Amberg summarising the company's findings. The researchers isolated around 70 different microbes from the washing machine biofilms, of which around one third belongs to risk class 2, meaning that they pose a potential risk to human health. Amongst the microbes identified were Pseudomonas aeruginosa, Burkholderia cepacia, Trichosporon sp. and Serratia marcescens. However, since the project is still ongoing, Caroline Amberg cannot disclose their findings.

In addition to its projects assessing the hygiene in washing machines and dishwashers and biofilm formation, Empa Testmaterials also carries out numerous standardised processes and routine hygiene tests. The tests, which include skin compatibility tests, disinfectant tests and investigations into biological degradability, are always adapted to specific issues, and the company's findings are always used to optimise methods. One particular example is the assessment of the antimicrobial effect of specifically finished textiles. "Immobilised antimicrobial finish cannot be tested using agar diffusion tests because the active agent does not diffuse. Silver layers are inactivated by high protein loads and we therefore need to reduce the protein load of bacterial suspensions when testing these kind of finishes," said Caroline Amberg. This helps prevent false results. Daniel Fäh explains: "Our utmost priority is to keep in mind the significance and potential limit of a certain standard, rather than blindly carrying out tests according to a certain standard."

In addition, the company, with its staff of 25, produces artificially soiled test fabrics to assess the effect of washing processes. Artificial soiling refers to standardised stains that are stable and deliver reproducible results when washed. “However, wine and blood soilings actually contain blood and wine, but they are stabilised and aged in order to generate consistent results with only small standard deviations,” said Daniel Fäh further explaining that the laundry industry is extremely interested in bleachable tea, fruit and wine stains, particularly in view of increasingly lower washing temperatures. “It also needs to be possible to remove stains that require enzymatic treatment, for example blood and milk, at low temperatures,” summarised the chemist.

Therefore, the test fabrics produced by Empa Testmaterials AG need to fulfil certain requirements in order to be used in different investigations and analyses and be considered “consumer relevant”. Relevant refers to the sensitivity of the test fabrics with regard to certain parameters, including enzyme efficiency, temperature, surfactant quantity and bleach, to name just a few. “In addition, the test fabrics must lead to reproducible results, they must show stable storage behaviour and it must be possible to differentiate between different products and applications,” said the company’s managing director.

Empa Testmaterials is also focused on the investigation and assessment of the efficiency of washing processes and washing machines. One such example is the assessment of the effects of enzymes contained in detergents using soiled test fabrics. The company applies soilings that are sensitive to enzymes such as amylase, protease, lipase, cellulase or mananase to fabrics. The fabrics are then washed and the brightening of the stains is subsequently determined with a spectral photometer, which provides information on the degree of stain removal.

Empa Testmaterials AG develops many of its test methods and materials in cooperative R&D projects with industrial partners. The company produces its test strips in cooperation with numerous regional companies in the Lake Constance area. The company also recently became a member of the BioLAGO network. In addition, the company is interested in working with washing machine and dishwasher manufacturers and their suppliers, detergent producers and their suppliers from Germany and abroad.

The main focus of the St. Gallen-based company is to find answers to questions relating to which detergents, washing methods or raw materials lead to the best results, i.e. do not damage the fabrics and discolour the fabric as little as possible, thereby resulting in perfect hygiene. “We are also open to working with testing institutes in the field of washing, cleaning and hygiene and with universities dealing with biofouling, biofilm analytics, biosensors or pathogen identification,” said Daniel Fäh.

Kontakt:

Caroline Amberg
Microbiologist
EMPA Testmaterials AG
Lerchenfeldstrasse 5
CH-9014 St. Gallen
Tel.: +41 71 274 76 14
Fax: +41 71 274 74 99
E-mail: caroline.amberg@empa-testmaterials.ch

Daniel Faeh
Managing Director
EMPA Testmaterials AG
Tel.: +41 71 311 80 55
Fax: +41 71 311 80 57
E-mail: daniel.faeh@empa-testmaterials.ch