wahing machine with germs

Spreading not cleaning – the case of the washing machine

Laundry is a necessary chore although since 1907, it has become far easier thanks to the automated washing machine1. In less than an hour even the most soiled clothing can look clean, smell fresh, and give us the chance to dirty it up again. The addition of detergents supposedly also makes them safe against the potential for infection due to bacteria, viruses, and fungi.

However, back in 19382, a study revealed that washing clothes in detergent was not as beneficial to our health as originally thought. The authors found bacteria could survive the washing process and end up not only on clothes, but also the surface of the drum, allowing growth. From a microbiological perspective, this makes perfect sense as bacteria have only three requirements for growth:  water, nutrients, and a temperature between 15 and 65 degrees Celsius.

Thankfully, researchers also learned how they could alleviate this concern. They could use hot water over 65 degrees Celsius as well as add in a disinfectant, such as bleach, to ensure that the clothes and drum remained safe. This led to the incorporation of hot water cycles and also the recommendation for the inclusion of bleach.

This protocol worked well until the 1970s when the world changed yet again. The introduction of textiles that were damaged in either hot water or bleach3 led to a reduction in use. Care labels4 were also included to provide recommendations to ensure minimal wear on fabrics. The focus on reduced energy use also grew during this time and recommendations for laundry changed from hot water to warm and even cold water5. The movements were both widespread and powerful leading to a significant shift in society. Unfortunately, very little attention was given to the potential for survival of bacteria and other potentially pathogenic microbial species.

But over the last five years, there has been a resurgence of interest in killing microbes in laundry thanks to the explosive rise of antibiotic resistance, which the World Health Organization called a crisis in 20146

World Health Organization

But over the last five years, there has been a resurgence of interest in killing microbes in laundry thanks to the explosive rise of antibiotic resistance, which the World Health Organization called a crisis in 20146. Many bacterial infections are no longer as easy to treat as they were in the 1970s and as such, reducing the potential for growth and spread of these species became a priority. Not surprisingly, the results of 1938 have pointed to the laundry tub as one of the most troubling culprits when it comes to the spread of bacteria.

Due to more modern microbiological analysis, the dynamics of washer contamination and spread have been given more attention. We now know biofilms can be found in many areas of the machine7 and they can grow to levels that can contaminate all the clothes in a wash. The amounts can be sufficiently high that the bacteria can give off a foul smell8 that can be transferred to the clothes. Add in antibiotic resistance and the potential for troubles is apparent.   

This latter point has been the focus of a German study published earlier this year in the journal, Applied and Environmental Microbiology9. The paper identifies the washing machine as the source for the spread of antibiotic-resistant bacteria in a healthcare facility. Perhaps more troubling is that the bacteria spread to some of the most vulnerable of us, infants in neonatal care. Based on their results, hats and socks were contaminated and picked up by the children while they wore the clothes. Making this study even more important is that as soon as the washing machine was taken out of use, the spread of the bacteria stopped.  

Upon looking more closely at the washing machine, there were two hotspots that revealed the most contamination. The first was not surprisingly, the rubber lining, which had already been shown to be capable of growing biofilms7. The other thought was rather surprising. It was the compartment where the detergent is loaded into the machine. This not only revealed the lack of bactericidal activity on the part of the detergent but also revealed that any surface can be a risk for contamination.

If one cannot take a washing machine out of service, then there are some useful ways to prevent this contamination. The first is to run an empty hot water wash with bleach to return to the tried and trusted means to kill bacteria. The other is to use a disinfectant to clean all the surfaces of the drum and the detergent compartments.  

As for auditing the washing machine, there are few ways to test it. One involves swabbing and culturing the drums and other surfaces. Another is to stop the cycle intermittently and take water samples. Both will provide some indication of the potential for spread.

There is a third method that may be of significant value to institutions that rely on washing for their continuance of business. A real-time visual identification of organic contamination on surfaces such as the Optisolve Pathfinder could provide not only real-time visual results of the cleanliness of washers but may also offer an indication as to hotspots that would require greater attention. This, in turn, could lead to improved cleaning and a reduced risk for transmission of pathogens to customers, clients, or patients.

The washing machine is without a doubt a necessary part of modern-day living however it does come with its microbial risks. In the antibiotic resistance era, the reduction of spread of bacteria to clothes is more important than ever. With proper surveillance and subsequent action, we may be able to improve our ability to keep washing machines clean so that when laundry is done, we’re getting exactly what we want:  clothes that are clean, fresh-smelling, and most of all, safe.  


  1. https://edisontechcenter.org/WashingMachines.html
  2. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1529034/  
  3. http://calag.ucanr.edu/archive/?type=pdf&article=ca.v031n01p18
  4. https://onlinelibrary.wiley.com/doi/abs/10.1177/1077727X8000800507
  5. https://www.osti.gov/servlets/purl/6272872
  6. https://www.who.int/mediacentre/news/releases/2014/amr-report/en/
  7. https://www.tandfonline.com/doi/abs/10.1080/08927014.2010.524297
  8. https://sfamjournals.onlinelibrary.wiley.com/doi/full/10.1111/lam.12050
  9. https://aem.asm.org/content/85/22/e01435-19
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