Danish research shows that the quantity, composition and diversity of bacteria in T-shirts is highly individual. Several factors determine these differences, and this may be relevant for both clothing and detergent manufacturers.
We all have bacteria on our skin, and they end up infiltrating our clothes.
However, the number and types of bacteria on my clothes differ substantially from those on your clothes. In this sense, we are all vastly different.
This is what new Danish research shows. The researchers also identified several reasons why the composition of the bacteria on T-shirts differs between individuals and between T-shirts. The research was conducted in collaboration between researchers from the Department of Biology at the University of Copenhagen and Novozymes.
“The bacteria in the armpit of the clothes determine the odour and also somewhat how durable the clothing is. Knowing which factors determine this is therefore useful for manufacturers of clothing and laundry detergent. In this study, we not only identified some factors that affect the bacteria but also developed a method for analysing them in clothing that people have been wearing,” says a researcher behind the new study, Mette Burmølle, Associate Professor, Department of Biology, University of Copenhagen.
The research results have been published in Environmental Research.
Difficult to investigate the bacteria in a T-shirt
Determining which bacteria are present in a T-shirt has been difficult for researchers.
This is because it is not easy to extract bacteria from fabric and determine the quantity, composition and diversity of these bacteria.
Some researchers put an entire T-shirt in a solution that releases the bacterial DNA; others cultivate the bacteria from a sample of material in a laboratory growth medium to increase the number of bacteria that can be analysed.
However, both methods have limitations.
Analysing bacteria from an entire T-shirt is unworkable for very practical reasons because of the difficulty in creating a laboratory setup with 500 T-shirts in buckets around the laboratory for extracting the bacteria. In addition, important information is missing on where specific bacteria were located on the T-shirt.
Cultivating the bacteria in a petri dish is also a bad idea because some will grow faster than others and bias the ratios between the species.
“We worked for quite a while to develop the appropriate methodology. But we developed a technique in which we can take a 10 by 10 cm piece of fabric from the armpit, extract the bacteria from the fabric and perform 16S rRNA gene amplicon sequencing and quantitative PCR to estimate both the absolute abundances of bacteria and the relative distribution of different genera of bacteria,” explains Mette Burmølle.
Research project resulted from a thesis
The entire research project actually stems from a master’s thesis project that former student Eva Sterndorff carried out in collaboration with Novozymes.
She asked 10 men (4 office workers, 3 students, 2 bicycle mechanics and 1 police officer) to each put on a T-shirt and wear it for three days, both day and night.
The T-shirts were made of different materials: some cotton and others polyester.
Subsequently, Eva Sterndorff and the research team used the newly developed technique to analyse the bacteria from the T-shirts.
They examined the T-shirts the 10 men had worn, T-shirts that had just been opened from the manufacturer’s packaging and T-shirts recently washed in mild detergent without enzymes.
“The T-shirts were laundered at Novozymes, which has a very special setup for washing T-shirts in different ways with or without the enzymes that are usually added to laundry detergent to remove grime and dirt more efficiently. In this study, we used a mild detergent without enzymes,” says Mette Burmølle.
Differences between people and between fabric types
The study found the following results.
• New and unworn cotton T-shirts already had measurable bacterial load, whereas new and unworn polyester T-shirts had no detectable bacteria.
• The total quantity of bacteria in the armpits of T-shirts did not change very much when laundered with a mild detergent. The composition of the bacterial community changed, but the total quantity of bacteria did not.
• When worn, the polyester T-shirts accumulated more bacteria than cotton T-shirts. Laundering with mild detergent reduced the total quantity of bacteria only slightly for both cotton and polyester T-shirts that had been worn.
• The individual wearing the T-shirt was the most important factor in determining microbial composition and diversity.
“The results show that the most decisive factor is who wears the T-shirt. This determines the quantity and composition of the bacteria,” says Mette Burmølle.
Personalized laundry detergent in the future?
Mette Burmølle explains that several factors determine an individual’s underarm bacteria, which subsequently colonize the T-shirt.
These include the inherent differences in people’s bacteria, differences in activity level and thereby the amount of sweat under the armpit, genetics, diet and where people are during the day.
“The study was very small because it was primarily intended to develop a method for extracting bacteria from clothing. Nevertheless, we found some differences, and these may be relevant for both clothing and detergent manufacturers. Perhaps in the future, you can not only choose laundry detergent for clothes according to colour but more importantly based on the type of fabric and on your microbiome,” says Mette Burmølle.
“The T-shirt microbiome is distinct between individuals and shaped by washing and fabric type” has been published in Environmental Research. In 2017, the Novo Nordisk Foundation awarded a grant to Mette Burmølle for the project Biofilms as Accelerators of Co-evolution for Improving Bacterial Consortia Performance.