Climate Change Droughts May Fuel Antibiotic-Resistant Bacteria

Growing droughts linked to global climate change may be producing ideal circumstances for antibiotic-resistant bacteria to develop, a new study suggests.

The overuse of antibiotics in healthcare is apparently not the sole force behind the rise of resistant bacteria. The findings indicate that processes occurring beyond hospitals, in the Earth's soils, may also affect antibiotic resistance in healthcare environments.

Research led by scientists at the California Institute of Technology (CIT) shows that drought can increase concentrations of naturally occurring antibiotics in soil, encouraging microbes to develop antibiotic-resistant genes.

As climate change makes droughts more common, severe and extensive, microbes equipped genetically to withstand these heightened concentrations of soil antibiotics may gain a survival advantage.

Bacteria were making antibiotics in soil long before humans began using such compounds as medicines. They do so to gain an edge over rival microbes.

"Likewise, antibiotic-resistant bacteria, and the genes that confer their resistance, long predate human medicine, having evolved as natural defenses against antibiotic-producing bacteria," explains microbial ecologist Timothy Ghaly of Macquarie University in Australia, who did not take part in the research, in an accompanying perspective.

This, he says, "raises a pivotal question: What environmental factors might promote the spread of antibiotic resistance genes from the reservoir of soil bacteria into the built environment and clinical human pathogens?"

Drought, soil microbes and antibiotic resistance

To investigate, the CIT researchers examined five datasets from studies involving soil samples gathered in the US, China and Europe. These datasets recorded drought's effect on soil microbial communities in a variety of settings, including farmland, grassland, woodland and wetlands.

All five datasets showed that drought was associated with greater quantities of genetic material from antibiotic-producing bacteria, alongside genes known to provide antibiotic resistance.

Put simply, bacteria found in soil samples affected by drought seemed more capable of withstanding exposure to antibiotics.

In related laboratory tests, the researchers introduced an antibiotic into a small-scale soil ecosystem, then dried the system to recreate drought conditions. This caused the antibiotic to become more concentrated within the soil.

Bacterial species that were already resistant to the antibiotic survived equally well in dry and moist soils. However, strains susceptible to the drug were almost completely eliminated under the 'drought' conditions.

Some of the survivors were antibiotic-producing bacteria, which are naturally resistant to the compounds they produce themselves. Ultimately, both antibiotic producers and antibiotic-resistant bacteria became more abundant in the soil.

Climate change, drought and hospital antibiotic resistance

"Having established drought's role in amplifying antibiotic resistance in soil, the authors, in perhaps their most alarming finding, link this natural phenomenon to global public health," Ghaly explains.

When examining hospitals in 116 countries, the team identified an exceptionally strong association between how often antibiotic resistance occurred within hospitals and the local aridity index – a measure of how dry the outside climate is.

The relationship remained after the scientists accounted for national income, which can influence both antibiotic use and healthcare systems more broadly.

"This suggests that a core driver of clinical resistance operates via a global environmental mechanism, whereby climatic conditions in natural ecosystems can influence pathogen evolution in the built environment, and ultimately human health," Ghaly writes.

Implications for clinical settings

Although the evidence is insufficient to establish that droughts cause increased antibiotic resistance in clinical settings, it does indicate that climate change – particularly the droughts it is worsening – may raise the risk.

"Our study offers a clear example of how climate change has the potential to intersect with microbial ecology to shape public health outcomes… [underscoring] the importance of integrating environmental and clinical perspectives… " the authors conclude.

"As climate instability intensifies, such integrative approaches will be critical for anticipating and mitigating the global trajectory of antibiotic resistance… "

The research appears in Nature Microbiology.