Research

Bacterial exchange in washing machines

Unpleasant odors can still be present, even after washing your clothes in the laundry machine. We investigated what is going on in our laundry machines: what goes in and what goes out; and what kind of microbial exchange occurs in there.

Bacteria stick to the clothes after washing on 30°C and with mild detergents

In the past decennia, there was an evolution towards lower washing temperatures and mild, eco-friendly washing detergents. Nowadays, clothes are washed at 30°C and with detergents without bleaching agents. This is good for the environment, but the impact on the bacteria was not yet known. The washing machines of five different Flemish families were investigated. They laundered in normal household washing machines, using a mild program at 30°C with a detergent without bleach. A clean cotton piece of textile was laundered together with the used clothes of the family and was studied before and after laundering. Also the influent and effluent water of the washing machine was investigated. 

Bacteria on cotton piece and effluent water

In the washing machine, a high exchange of bacteria from the influent water, the washing machine and the dirty laundry load was noticed. The cotton piece typically attracted specific skin- and clothes-related bacteria. Certain species have a higher affinity to adhere to the clothing textiles than others. On the cotton piece, practically no fecal or pathogenic bacteria were retrieved. The majority of the bacteria are moreover commensal bacteria, which live in harmony with us without causing any harm. So there is definitely no risk for public health.

Even after laundering, up to 1 million living bacteria were found per milliliter of effluent water (under the circumstances of our study). Only low amounts of bacteria from the influent water were retrieved in the cotton pieces, even when recycled rainwater was used (known to contain large amounts of bacteria). The water-related bacteria were predominantly retrieved in the effluent water.

Clothes have their own microbiome and their own odor

Ever wondered why clothes always develop the same odor? This is because the clothes develop their own microbiome. The same odor-causing bacteria return after laundering, and can cause a specific odor when the clothes are used again. The odor-causing bacteria adhere very well to the clothes and are not washed out with the washing machine. 

The full open-access article is available at Frontiers in Microbiology

 


 

The bacterial and odor profile of our sport clothes

After sports, your sport clothes can get quite smelly. Some people may have noticed that the type of clothing textile also has an influence on the malodor formation. Our research team investigated this and has identified the typical odor causing textile types, but also the bacterial strains responsible for this odor. Polyester clothes smell worse than cotton, following intensive exercise by their wearers, because bacteria that cause odor grow better on polyester. We collected t-shirts from 26 healthy individuals following an intensive, hour-long bicycle spinning session, and incubated the shirts for 28 hours before having them inspected by a trained odor panel. We also investigated the taxonomy of the bacteria on the shirts and in the axillaries. Freshly secreted sweat has little odor, because the long-chain fatty acids the axillaries secrete are too big to be volatile. Bacteria break these, as well as hormones and sulfur compounds, down to smaller, odoriferous molecules. We particularly found micrococci able to grow on the polyester clothing textiles. This finding was confirmed in an in vitro experiment. Micrococci are known for their enzymatic potential to transform long-chain fatty acids, hormones, and amino acids into smaller, volatile, compounds, which have a typical malodor. Staphylococci, which inhabit both axillary skin and adjacent textiles (the latter with much less diversity), create a normal, non-malodorous body odor. Interestingly, corynebacteria, which are the main cause for malodor in the armpits, were not able to grow on the textiles. Apparently, they need the more anaerobic environment of the human skin to grow. 

A preview of the article can be found in Applied and Environmental Microbiology; a news story can be found in Popular ScienceAAAS Science magazineNPRScientific American and nu.nl.

 


 

Staphylococcus and Corynebacterium clusters in the human axillary region

The human armpit is still a piece of mystery. Therefore, this research studied the bacterial flora in the armpit by sampling over 50 people and resampling some of them during a year. Two bacterial genera always occurred in the armpit: staphylococci and corynebacteria, as 77% of all sequences were assigned  to those two bacterial groups. The corynebacteria are known to cause malodor in the armpit, whereas staphylococci are known to cause no significant malodor.

The research showed that, although the number of bacteria can go very high, the number of different bacteria was rather low. On average, only 33 unique different phylotypes were found per armpit. This is half as much as in the human belly button, where 67 bacterial phylotypes were found per belly button. Five times more different bacteria are found on the hand palms, where 158 bacterial phylotypes were found per hand. So next time you give someone a hand, think about the exchange of the tremendous amounts of different bacteria. 

This research showed that, when more deodorant was sprayed in the armpit, the diversity of different bacteria increased in the armpit. How do I understand this? If you don’t use deodorant, and you don’t wash yourself too often, very few different bacteria will occur there. If you do not have smelly armpits: keep it like that and don’t overuse deodorants. Because, if you’re using a lot of deodorants, more different bacteria will occur, and if one of those bacteria is an odor-causing bacterium, and he can suddenly take over, smelly armpits will be the results.

Female armpits are generally dominated by staphylococci, while males are likely to have more corynebacteria in the armpit. This is probably due to the fact that males have a thicker skin and sweat more fatty substances in the armpit, which is the favorite dish for the lipophilic corynebacteria.

It is likely that your left armpit is not identical to your right armpit. Small bacterial differences were found between left and right armpit in the half of the studied people. Only in some cases, this can express in a different odor between left and right armpit. The bacterial community was quite stable over a longer period, although a total shift was seen for both armpits of two people. The reason for this shift is still unknown, however, this implies that the armpit microbiome is able to reconfigure to another stable microbiome, and maybe into a less odorous armpit. Our research team will do anything within our power to make this possible for other people. Stay tuned for more updates.

The full article can be found in Plos One

 


 

Artificial sweat composition 

In our armpit research we have succeeded in making an artificial sweat composition. Yeej! And why do we what to do that? Simple: every person is different, and we need an objective method that does not have the variations every human being has. Based on literature, we composed a sweat composition which permits all armpit bacteria to grow in equal manners as they would do on the armpit skin. The axillary bacteria still resemble the original community after growing them for 21 days in the artificial sweat composition. Even the formed odor and malodor molecules resemble the original odors. 

The full article can be found in Journal of Microbiological Methods.

 


 

The effect of deodorants and antitranspirants on the armpit microbiome

Our previous study showed that the diversity is highly affected by the usage of deodorants. A survey indicated that 95% of the young adolescent people use underarm cosmetics. Our research team studied the effect of deodorants and antitranspirants on the armpit microbiology. We saw significant changes when deodorants and especially antitranspirants were used. We have asked eight people, who used underarm cosmetics on a daily basis, to restrain from using any deodorant/antiperspirant during one month. Another person, who did not use any underarm cosmetics was asked to start using a daily deodorant during one month. When deodorant/antiperspirant was used in a stable manner, the microbiome was quite stable over time. But when suddenly the usage was stopped or resumed, we saw big changes in the axillary microbiome. Especially antiperspirants showed a significant effect on the microbiome: the diversity increased and an increase of the Actinobacteria phylum was seen (containing the odor-causing Corynebacterium species). If the Corynebacterium spp. get more dominant, the subjects body odor can increase and change to a more sour/musky odor. It is believed that the aluminum salts in the antiperspirants have a higher impact on the Staphylococcus spp. than the Corynebacterium spp. 

The full article can be found in Archives of Dermatological Research; news stories about it can be found in RealClearScience, the Huffington Post and the Washington Post.

 


 

Armpit bacterial transplantation 

We are working an a new technique to counteract unpleasant armpit odor formation. The idea is to replace the malodorous armpit microbiome by a healthy non-odor causing armpit microbiome from a donor. We currently see the best results among family members. Updates are following.

 


 

The malodorous armpit microbiome

We have screened over 200 people with self-reported smelly armpits.  We analyzed the microbiome, the odor and the effect of the malodor on their daily lives. The results are astonishing; we received a profound view on the the malodorous microbiome and its effects. Currently working on this paper. For now just remember: if you have a body odor, it is not your mistake: it is the cause of your bacteria.