Drought Conditions Fuel Rise in Antibiotic Resistance

A recent study reveals a concerning link between drought conditions and the proliferation of antibiotic-resistant microbes, with implications for both environmental and human health. Researchers found that drought favors microorganisms that can survive in the presence of antibiotics, and that genes for antibiotic resistance present in soil-dwelling bacteria are increasingly appearing in pathogens found in hospital patients.

The Role of Horizontal Gene Transfer

Bacteria readily exchange genetic material through a process called horizontal gene transfer, allowing resistance traits to spread quickly. This means that an increase in antibiotic resistance within soil microbes can easily transfer to those that infect humans, according to the study authors. “No place is immune,” says Dianne Newman, a biologist at Caltech and the study’s senior author. “If you have a pathogen arise in one part of the world, it very quickly spreads, so this is something of concern regardless of where you live.”

Antibiotic Resistance: A Growing Global Threat

Antibiotic resistance is already a major public health crisis. The World Health Organization estimates that antibiotic-resistant pathogens directly caused 1.27 million deaths globally in 2019 and contributed to another 4.95 million. Antibiotics, although used to kill microbes, originate from microbes themselves – penicillin being a prime example derived from fungi. Microbes synthesize antibiotics as a defense mechanism in their evolutionary competition with other microbes, and soil serves as a major battleground for this evolutionary warfare.

How Drought Intensifies Resistance

Researchers, led by Caltech postdoctoral researcher Xiaoyu Shan, initially observed a correlation between drought and increased antibiotic resistance while analyzing five metagenomics databases containing soil microbe genetic information from around the world. They consistently found that antibiotic synthesis genes were more prevalent after dry periods and less common when drought conditions ended.

Laboratory experiments confirmed these findings. When soil-dwelling bacteria were exposed to the antibiotic phenazine and subjected to simulated drought conditions (drying for three days), the concentration of the antibiotic increased as moisture evaporated. This, in turn, led to a flourishing of antibiotic-resistant bacteria while those susceptible to the antibiotic suffered.

Global Evidence and Genomic Links

Further analysis of genomic data revealed that genes conferring antibiotic resistance were more common during dry periods. This increase coincided with a rise in genes for antibiotic synthesis, supporting the idea that drought-stressed microbes enhance their resistance as a response to increased antibiotic pressure from neighboring organisms.

When researchers analyzed soil samples from the Caltech campus treated with four different antibiotics, they again observed a higher prevalence of antibiotic-resistant microbes in the desiccated samples.

Climate Change and the Spread of Resistance

A global analysis, correlating data on antibiotic-resistant pathogens from hospitals worldwide with climate and weather patterns, revealed a significant association: the drier the region, the more antibiotic-resistant pathogens were reported in hospitals. This correlation remained even after accounting for socioeconomic factors that could influence pathogen testing.

Crucially, the researchers discovered that many of the genes responsible for antibiotic resistance in soil microbes were identical to those found in clinical pathogens, including Enterococcus faecium, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and various Enterobacteria species. This highlights the potential for resistance to transfer from soil microbes to human pathogens through environmental contact.

As Timothy Ghaly, a microbial ecologist at Macquarie University in Australia, notes, continued warming and drying trends are expected to expand arid conditions, potentially accelerating the problem of antibiotic-resistant pathogens.

Combating the Crisis

Addressing this growing threat requires a multi-pronged approach. Strategies include rapid diagnostic testing to quickly identify antibiotic-resistant infections, the leverage of multi-antibiotic treatments, and increased investment in basic research for new drug discovery. Newman emphasizes the need for continued government funding of scientific research and drug development, as pharmaceutical companies have largely reduced their efforts in this area due to profitability concerns.