New Delhi, March 25 Soil dryness caused by drought can increase the amount of natural antibiotics and promote the growth of antibiotic-resistant bacteria, according to an analysis.
The findings, published in the journal Nature Microbiology, suggest that the rise in soil dryness, driven by climate change, could heighten the risk of antibiotic resistance.
Comparing antibiotic resistance data from hospitals across 116 countries to local yearly precipitation and mean temperature, researchers from the California Institute of Technology in the US showed that a higher aridity (dryness) is associated with a higher average frequency of antibiotic resistance among clinical isolates.
The result suggests another way climate change may affect public health, they said.
Soils are a rich source of natural antibiotic compounds, and soil microbes have evolved mechanisms to survive an exposure to them.
However, even though many antibiotics are derived from soil microbes, how changes to the environment -- such as more frequent and prolonged droughts driven by climate change -- may affect the balance of antibiotic-producing and antibiotic-resistant microbes in soil is unclear, the researchers said.
Implications for human health, too, are not certain, they added.
For understanding how drying affects soil antibiotic dynamics, the authors compiled five metagenomic datasets from previous studies, including soils from a cropland and grassland in California, US, a forest in Valais, Switzerland, and a wetland in Nanchang, China.
The team found that the abundance of antibiotic-producing genes of soil microbes significantly increased under drought conditions across the datasets, including for antibiotics, such as penicillin.
In lab experiments, the researchers found that under drought conditions, antibiotic levels became more concentrated, with a 99 per cent reduction in the relative fitness of some antibiotic-sensitive bacteria strains – antibiotic-resistant ones however showed no reduction in relative fitness.
"Across various geographic regions and soil types, we consistently observe metagenomic signatures of enrichment for antibiotic producers under drought conditions," the authors wrote.
Experiments in the lab "demonstrate that drought-induced lowering of water content concentrates natural antibiotics, thereby intensifying selection against sensitive strains and favouring antibiotic-resistant bacteria," they said.
"Using clinical surveillance data from 116 countries, we show that the average frequency of hospital antibiotic resistance is strongly correlated with the local aridity index, even after controlling for regional income differences," the team said.
"Together, our findings reveal an under-recognised link between climate factors and antibiotic resistance," they said.