Every day, countless cars travel the roads, leaving behind tiny particles of tire material that most of us never notice. These tire wear particles (TWPs) are an invisible byproduct of our driving habits, but they may have a much larger impact than previously thought.
A study published in Environmental Research has brought a surprising threat to light: tire wear particles (TWPs). TWPs are tiny bits that come off your car’s tires during driving and may be playing an unexpected role in spreading antibiotic resistance.
Scientists from Germany, Italy, and other countries are leading this research, which explores how these micro-particles enhance the horizontal transfer of antibiotic resistance genes (ARGs) among bacteria in aquatic environments, with significant implications for both environmental and public health.
Most of us think of plastic pollution as bags or bottles in the ocean, but microplastics, which are tiny fragments of less than 5 millimeters, are also a significant concern. Among these, TWPs play a major role, being generated every time we drive.
Every year, millions of tons of these particles enter aquatic ecosystems, becoming one of the largest contributors to plastic pollution. What makes TWPs especially concerning is their complex makeup. Unlike other microplastics, they contain not just synthetic rubber but also a variety of metals such as zinc and lead, which might influence the internal molecular structure of bacteria.
The researchers wanted to understand whether TWPs could enhance the spread of antibiotic resistance in bacteria. Antibiotic resistance arises when bacteria adapt to endure exposure to drugs intended for their elimination, thereby presenting an increasingly pressing challenge in the treatment of infections.
The team specifically looked at how TWPs could affect the horizontal gene transfer (HGT) process, a mechanism that allows bacteria to pass antibiotic resistance genes to each other. They did this by studying how bacteria interacted with TWPs compared to other surfaces, including polystyrene plastic and natural materials like chitosan.
The scientists used two types of bacteria: a donor strain of Escherichia coli carrying an antibiotic resistance gene, and a recipient strain of Pseudomonas bacteria. They tagged the E. coli with a fluorescent marker to track gene transfer. They introduced this to Pseudomonas bacteria as well as to a natural lake microbial community to observe if and how the resistance gene transferred in the presence of TWPs.
The results were remarkable. The presence of TWPs significantly boosted the transfer of antibiotic resistance genes between bacteria compared to other surfaces like polystyrene and chitosan.
Lead researcher Yousuf Dar Jaffer said, “Our results show that TWPs can be useful hotspots for the exchange of antibiotic resistance genes. This is mostly because they can attract different types of bacteria and make gene sharing easier within biofilms.” These biofilms formed quickly on the surface of TWPs, creating perfect environments for genetic exchange.
Interestingly, the metals present in TWPs played a significant role. Heavy metals like zinc and lead tend to stress bacteria, and this stress can make bacteria more likely to share genes, including those responsible for antibiotic resistance. The study showed that metals in TWPs elevated the rate of horizontal gene transfer even more.
“We were particularly surprised by how effectively the metals facilitated this process,” said co-author Fazel Abdolahpur Monikh. “They act as a catalyst, increasing the frequency of genetic exchanges between bacteria.”
They also found that temperature had a significant impact on how effectively TWPs could promote this genetic exchange. At higher temperatures, typically found in warmer aquatic environments, the frequency of horizontal gene transfer increased significantly. The researchers noted that even at lower temperatures, like those in natural lake environments, the presence of these micro-particles still led to heightened gene transfer compared to scenarios without tire particles. This finding is alarming considering the potential impact of rising global temperatures due to climate change.
The real-world implications of this research are significant. Antibiotic resistance is a pressing global health issue that makes it harder to treat common infections and increases the risk of severe health complications. The fact that tire particles can contribute to this problem means we need to rethink how we manage tire waste and explore ways to reduce the release of TWPs into the environment. Despite conducting the research under controlled conditions, the findings suggest that TWPs may be an overlooked contributor to the growing issue of antibiotic resistance in natural ecosystems.
The research could pave the way for new policies or technologies aimed at reducing TWP pollution. For instance, there might be a push to develop eco-friendlier tire materials or improved tire designs that minimize particle shedding. Additionally, we could adjust urban planning and stormwater management systems to limit the entry of these particles into natural water bodies.
“Our study highlights the need for both technical innovation and policy intervention,” said Hans-Peter Grossart, another co-author of the study. “Reducing the environmental release of tire wear particles could be crucial in combating the spread of antibiotic resistance.”
Tackling this problem will require cooperation between environmental scientists, engineers, policymakers, and the tire manufacturing industry. This study serves as a wake-up call to the unseen ways in which everyday products can influence our environment and health in profound ways.
For more information, visit: https://doi.org/10.1016/j.envres.2024.120187
