Tyre particles may help antibiotic resistance spread through cities

Whenever a vehicle travels along a road, it leaves behind a small amount of rubber. It is now widely recognised that this dust contaminates the air, water and soil.

Less apparent, and somewhat troubling, is the possibility that these minute particles could play a far more subtle role.

They may form small environmental pockets in which bacteria retain antibiotic resistance genes, pass them between themselves and distribute them across cities.

Less apparent, and somewhat troubling, is that these tiny particles could have an even more covert effect.

They can form small environmental hotspots where bacteria preserve antibiotic resistance genes, share them and disperse them throughout cities.

Tyre particles are continuously produced by friction between rubber and the road surface. They then spread widely: into the atmosphere, through surface-water drains, into riverbed sediment and across urban soils.

Tyre pollution does more than spread

“Tire microplastics should not be viewed simply as passive particles that carry pollutants from one place to another,” said corresponding author Yuyi Yang of the Wuhan Institute of Technology.

“Their surfaces, chemical additives, and aging processes may work together to create conditions that favor the persistence and transfer of antibiotic resistance genes.”

Tyres are not made of plastic alone. They comprise rubber, fillers, plasticisers and numerous additives containing more than 200 organic compounds.

Roughly two-thirds of these compounds may leach out as a tyre degrades.

In heavily populated cities, the quantities soon mount up. Tyre particles are estimated to account for more than 13 percent of fine particulate pollution in urban air, while levels in rivers and sediments near high-traffic areas can reach unexpectedly high concentrations.

The researchers describe three mechanisms through which tyre microplastics may actively intensify antibiotic resistance.

Tyres support microbial communities

Firstly, tyre particles are particularly effective at hosting dense microbial communities, which scientists have begun to call the tyre plastisphere.

This community differs noticeably from the biofilms that develop on other microplastics.

When large numbers of bacteria gather on a surface of this kind, resistance genes can move more readily from one microbe to another through horizontal gene transfer.

Bacterial groups already associated with carrying resistance genes, including Rhizobiales and Sphingomonadales, occur regularly within these tyre-based communities.

A chemical advantage for resistance

Secondly, the chemical composition of tyres is relevant.

Tyre particles release a complex blend of substances, including metals such as zinc, antioxidants, benzothiazoles and various organic compounds.

Some of these chemicals seem to place bacteria under selective pressure that benefits resistant strains, enabling them to survive and spread more effectively.

Ageing tyres become more reactive

Thirdly, there is the issue of ageing. As tyre particles remain in sunlight and gradually degrade through oxidation, they become chemically more reactive, producing reactive oxygen species and persistent free radicals.

To a certain extent, this increased reactivity seems to make bacterial cell membranes more permeable, promote biofilm formation and accelerate gene transfer.

However, the relationship is not linear. Once oxidative stress becomes too severe, it instead starts to harm bacteria and their genetic material.

The net outcome is likely to depend on the extent to which a particle has weathered and on the conditions to which it is exposed.

Testing tyre chemicals separately

In their review of the scientific literature, the researchers identified only seven studies that directly investigated tyre particles or tyre chemicals.

These studies considered links with antibiotic resistance genes, resistant bacteria or gene transfer.

Considering the possible consequences should this pattern prove correct, this represents a notably limited evidence base.

To narrow this knowledge gap, the team suggests adapting an approach already used for other environmental toxins: toxicity identification evaluation.

This would involve dividing tyre leachate into separate chemical fractions and testing each fraction to establish its effect on plasmid transfer between bacteria.

Preventing the spread of resistance

The practical message is straightforward: tyre particle pollution should be reduced as near to its source as possible, before it enters urban waterways.

The authors highlight several existing options, including stormwater filtration, roadside capture systems, green infrastructure and nature-based treatment systems.

Such measures are intended to capture particles before they enter rivers, soils and the wider urban environment.

Alongside physical interventions, the authors urge more coordinated monitoring that connects environmental management with public health and antimicrobial resistance initiatives.

At present, tyre pollution is generally regarded as an environmental nuisance, despite meriting a role in the broader effort to tackle antibiotic resistance.