Because discarded plastic appears to make an important contribution to the threat of resistance to antibiotics.

We are currently experiencing some major health crises. In addition to the corona pandemic, there has been a threat of increasing resistance to antibiotics for some time. This means that hundreds of thousands of people die every year from infections that could still be treated with antibiotics in the 1960s and 1970s. In addition, we are also suffering from an environmental crisis, in which we pollute our planet with microplastics. And researchers have now discovered that one may well amplify the other.

microplastics
Microplastics are small (often microscopic) pieces of plastic. People can inadvertently ingest small pieces of plastic when eating various foods, or simply by breathing air containing microplastics. Although larger particles find their way out through our stools, smaller pieces may be absorbed by our body. But what exactly are the consequences of this? We do not know yet. What we do know is that microplastics can potentially carry disease-causing bacteria. They can also contain bacteria that make us resistant to antibiotics.

In a new study the researchers examined polystyrene; a plastic that is widely used for cheap pressed objects such as disposable cups and chip trays. According to the scientists, discarded polystyrene, broken down into microplastics, provides a comfortable home not only for microbes and chemical contaminants, but also for certain genes that give bacteria the gift of resistance. In other words, discarded plastic chip trays could well contribute to the rise of resistant bacteria.

How does it work?

How does that work? When plastic, such as discarded French fries or cups, ends up in the environment, it can be broken down into smaller and smaller pieces by, among other things, UV radiation from the sun. These microplastics can then form a platform on which pathogens thrive and on which they can exchange antibiotic-resistant genes.

Sensitivity

Moreover, the longer a piece of plastic has been present in the environment, the greater the chance that it will contribute to the spread of resistant bacteria. The chemicals that leak out of microplastics over time appear to increase the sensitivity of microbes to horizontal gene transfer (see box). “We were surprised to find that the aging of microplastics enhances the transfer of antibiotic-resistant genes,” said study researcher Pedro Alvarez. “This enhanced spread of antibiotic resistance is an overlooked potential consequence of microplastic pollution.”

Repeated exposure to antibiotics can cause bacteria to stop responding to antibiotics after some time. But bacteria can also become resistant overnight, through a so-called horizontal gene transfer. Here, genetic material is exchanged between a resistant microbe and a non-resistant microbe.

In particular, the researchers found that very, very small microplastics (with a diameter of 100 nanometers to 5 micrometers) that have been broken down by UV rays from the sun, have quite large surfaces on which microbes can nest. During the decomposition process, the plastic then leaks, as mentioned, harmful chemicals that break through the membranes of the microbes. This gives antibiotic-resistant genes even more chance to ‘invade’.

breeding grounds

According to the research team, the surfaces of microplastics can serve as true breeding grounds for sensitive bacteria. Moreover, because the bacteria come into contact with each other and with the released chemicals, the gene transfer can be accelerated. That synergy could contribute to the rapidly growing problem of antibiotic resistance, even in the absence of antibiotics, the researchers say.

In short, it means that plastic that leaks chemicals attracts bacteria and also makes those bacteria more susceptible to the exchange of antibiotic-resistant genes. These results are alarming. Multi-resistant bacteria are one of the biggest problems for public health worldwide in the near future. Estimates indicate that by 2050, more people may die from infections caused by multidrug-resistant microorganisms than currently from cardiovascular disease or cancer. Identifying new antibiotic-resistant bacteria and genes could therefore play an important role in slowing the global spread of resistance. In addition, this is also another reminder that as a global community we should do more to look for ways to reduce plastic pollution worldwide.