Fed to Pigs, Lost to Medicine

Colistin was widely used as a growth promoter and prophylactic in livestock, particularly in China, from the early 1980s. It was cheap, effective, and considered safe for agricultural use because it had been largely abandoned in human medicine due to kidney toxicity — an "irrelevant-to-humans" framing that seemed like a free lunch. But as other antibiotics failed against multidrug-resistant gram-negative bacteria, colistin was revived as a "last resort" in human medicine. Meanwhile, decades of agricultural use had already selected for resistance. In 2015, Liu et al. discovered mcr-1 — the first plasmid-mediated (horizontally transferable) colistin resistance gene — in E. coli from Chinese pig farms. Unlike chromosomal resistance, plasmid-mediated resistance can spread rapidly between bacterial species. Before China's ban, mcr-1 was found in 21% of food animal E. coli isolates. The agricultural success destroyed the medical lifeline.

AMR already kills an estimated 1.27 million people directly per year (2019 Global Burden of Disease), with projections of 10 million annual deaths by 2050 without policy change (O'Neill Review). Colistin is the last effective treatment for some carbapenem-resistant Enterobacterales infections — losing it means losing the end of the antibiotic line. The mcr-1 gene has been found worldwide. Approximately 73% of global antimicrobials are consumed by livestock, and global agricultural antibiotic use is projected to rise 18.6% to ~131,000 tonnes by 2030.

China banned colistin as a growth promoter in April 2017. The ban was remarkably effective in the short term: colistin-resistant E. coli in pig feces dropped from 34% (2015–16) to 5.1% (2017–18); mean colistin residue in farm environments dropped from 191.1 μg/kg to 7.5 μg/kg; mcr-1 relative abundance fell from 0.0009 to 0.0002. But resistance has not been eliminated — the plasmid persists at low levels and can resurge if selection pressure returns. Other countries continue agricultural colistin use. The EU banned colistin as a growth promoter earlier, but therapeutic use continues. The fundamental problem is that mcr-1 is a horizontally transferable plasmid — once it exists in the bacterial gene pool, it cannot be easily removed. The "problems of success" mechanism is temporal: the agricultural decision was rational at time of adoption but catastrophic in retrospect, once the medical landscape shifted.

Global coordination to ban agricultural colistin use (not just growth promotion but also prophylactic use). Development of alternative growth-promoting strategies (probiotics, prebiotics, organic acids, improved biosecurity). Surveillance systems that detect resistance gene emergence before clinical failure occurs. New antibiotic classes that could serve as alternatives to colistin for multidrug-resistant gram-negative infections.

A team could design a low-cost surveillance tool for detecting mcr-gene variants in farm environments or wastewater, using isothermal amplification or CRISPR-based diagnostics suitable for field deployment. Alternatively, a team could model the dynamics of mcr-1 plasmid persistence under different scenarios (complete withdrawal, partial use, no intervention) to predict when — if ever — resistance prevalence would return to pre-use levels. Molecular biology, epidemiological modeling, and point-of-need diagnostic design skills apply.