Study finds heatwaves inhibit antibiotic resistance in soils

Bacteria that develop and resist antibiotics prioritise pure survival in heatwaves, temporarily reducing the presence of resistance genes.

Research by soil ecologist Franciska de Vries and colleagues at the University of Amsterdam found that bacteria switch to pure survival measures during heatwaves and consequently see a reduction in antibiotic resistance gene production.

However, heat and drought still cause major overall damage to soil and ecosystems, especially in areas that are typically wetter and colder, such as the Netherlands.

Soils provide both antibiotics and resistance genes

According to De Vries, many people do not know that soils are an important reservoir of both antibiotics – and we also get that from the soil – and resistance genes. ‘In the soil, it’s a kind of “war”: bacteria produce their own antibiotics and arm themselves against them with resistance genes,’ she explains.

In warmer temperatures and humid conditions, the presence of resistance genes increases, meaning more bacteria become immune to antibiotics. If this immunity spreads, bacteria that cause diseases in crops, animals or humans can develop more antibiotic resistance, making treatment more difficult.

Climate change is thought to accelerate the spread of resistance genes, but De Vries and her team were curious about how this scenario plays out during extreme weather conditions that occur rapidly, like heat, drought and floods.

Soils from all over Europe were tested in climate chambers

‘Before we got to this specific question, we first wanted to understand in general how soil organisms respond to extreme weather conditions,’ says De Vries. ‘Soils, for example, are very important for retaining CO₂. What happens to this function during extreme weather?’

Soils were collected from all over Europe: ‘from Iceland to Greece and from Sweden to Spain and even the Russian steppe.’

The researchers exposed these soils to extreme conditions in climate chambers: severe drought, flooding, alternating frost and thaw and a short but intense heat wave.

Researcher predictions about how each soil would react to extreme weather conditions were broadly accurate. ‘Quite logically, hot soils can withstand heat better than cold and wet soils such as those we have in northern Sweden, Iceland and the Netherlands,’ says De Vries.

‘Soils from warm, dry countries are already used to heat and drought,’ she adds. ‘There, the soil organisms remain relatively stable when the weather becomes extreme. In wet, cold soils, bacteria and fungi are disrupted much more quickly by heat and drought. These soils then lose their functions more easily, such as CO₂ storage. And it is mainly these areas that are warming up a lot.’

Testing the predictability of antibiotic gene resistance in soils

Using new DNA techniques, the study examined the effect of extreme climate conditions on the type and amount of resistance genes in soils, as well as how predictable the impact is.

Drought, flooding and frost-thaw periods were found to cause only mild changes in the resistance repertoire. Moreover, these reactions were reasonably easy to predict based on climate and soil type.

However, heat waves stood out. Here, the reactions were the least predictable and bacteria had a remarkably hard time. ‘They exchange fewer resistance genes and produce fewer antibiotics,’ says De Vries. ‘That was very surprising: just like plants, they also go into survival mode. And after such an extreme, those genes don’t grow back remarkably fast.’

Geography turned out to be decisive. ‘Where the soil comes from is more important than what extreme weather is unleashed on it,’ says De Vries. ‘Wet soils find it much more difficult to deal with drought and heat, while in countries such as Greece and Spain we saw much larger amounts of resistance genes.’

A temporary dip is unlikely to have an impact on the wider risk of growing antibiotic resistance

Although reducing antibiotic resistance might seem like a silver lining to the extreme weather impact brought on by climate change, De Vries warns that the overall damage caused to soil ecosystems by heat and drought are still a cause for concern.

‘We now know that climate extremes do not always affect antibiotic resistance in the same way,’ De Vries concludes. ‘This knowledge helps to better predict where the real risks lie and to tailor policy and monitoring to specific soils and regions.’