Authors of the Furtwangen University study: PhD student Sabasadat Seyednikkhoo and Prof. Markus Egert
Furtwangen University publishes new study on bacteria in smelly washing machines
Almost every private household in Germany has a washing machine. What many consumers do not realise is that washing machines, which are actually designed to clean fabrics, can harbour germs. Moisture, heat and an abundance of nutrients create ideal conditions for the growth of microbes such as bacteria and fungi. Current trends such as washing at low temperatures, water-saving programmes and the use of bleach-free liquid detergents can encourage the growth of germs. These germs do not pose an immediate risk of infection, but they can contribute to the formation of unpleasant odours.
“Why laundry and washing machines sometimes smell bad, however, remains a mystery,” explains study leader Prof. Dr Markus Egert, who teaches microbiology and hygiene at Furtwangen University (HFU) on the Schwenningen campus. “The typical ‘stinky’ microbe has not yet been identified. And our current study also suggests that there probably isn’t just one such microbe,” explains Egert.
Staff and students at Furtwangen University were asked to take part in the current study. This resulted in a sample of eight machines with an unpleasant odour and eight control machines without any particular odour.
Swab samples were taken from three different locations in the machines (detergent dispenser, porthole seal, sump), DNA was extracted from these, and the bacterial community was then analysed both qualitatively and quantitatively. This was the first time that ‘nanopore sequencing’ had been used for washing machines – a method that allows bacteria to be reliably identified at species level.
“Overall, the species composition and bacterial diversity in machines with and without odours were surprisingly similar,” summarises Egert. The bacterium Moraxella osloensis, which is often blamed for laundry odours, was, for example, very common in the door seal but showed no significant differences in abundance in relation to unpleasant odours. However, significant differences in relation to unpleasant odours were found for a handful of rather rare species, particularly those from the detergent dispenser. “Perceptible odour compounds do not always have to originate from common microbes. Even rare microbes could smell strongly. Whether the species identified here really play a role in the machine’s odour, however, would first have to be shown by follow-up studies,” says Egert.
It was striking, however, that the malodorous machines at all three test sites showed a tendency to have higher levels of bacterial DNA than the machines without any odour. “Perhaps it is simply the sheer quantity of bacteria that is responsible for one machine smelling musty to its owner and another not,” speculates Egert. The well-known measures to combat odours from washing machines (regular washing at a minimum of 60 degrees using a heavy-duty detergent containing bleach, allowing the machine to dry thoroughly between washes, and regularly cleaning all accessible surfaces with a neutral cleaner) are therefore still recommended.
“However, odour is also a very subjective matter,” Egert notes in conclusion. Follow-up studies should therefore not only examine more washing machines but also incorporate more objective odour analysis.
The new study was carried out by a research team from Furtwangen University and Henkel AG & Co. KGaA, and was supported by the BMFTR (Federal Ministry for Research, Transfer and Space) as part of the ‘FH Kooperativ’ funding programme. It has been published in the journal ‘Applied Microbiology and Biotechnology’ under the title ‘External link opens in a new window:Bacterial communities in domestic washing machines associated with user-perceived odours'.