Drug-resistant genes spread through environment, not meat products.

New findings show that traffic from humans to animals, and back to humans via the environment,is responsible for resistant genes and as such a new focus on tackling antibiotic resistance is proposed. 

In the first study to track antibiotic resistance in intensively-farmed beef, scientists discovered a "startling" lack of resistance genes in meat. Meanwhile, in soil and feces samples from cattle pens they found genes resistant to a powerful "last resort" class of antibiotics called carpabemens that aren't used in the livestock industry.

These genes may have jumped from humans or companion animals to livestock, or could even be present at low levels in the wider environment.

 Results published in eLife suggest researchers and policy-makers need to switch focus to combat the growing problem of drug-resistant bugs. A current focus for policy-makers is to reduce antibiotic use in livestock to curb the spread of drug-resistant bugs.


The team urges that traffic from humans to animals, and back to humans via the environment, should be a new focus for research. The lack of resistance genes in post-slaughter meat samples was a big surprise for the scientists, forcing them to rethink the view that it is only antibiotic use that increases resistance.

 Environmental routes of exposure are much harder to trace and have been largely overlooked by researchers and policy-makers. While many people never step foot on working farms, we are physically connected to agriculture via waste water run-off and wind borne particulates.

 The scientists suggest investigating wind patterns and water flow to see if, and how, resistant bacteria may be disseminated, and how far.

 The researchers opined that they may observe that such dissemination is very limited geographically, or we may find that resistant bacteria can travel long distances if they find the right currents or the right waterways. In either case, this would be very important information from a public health perspective.

 The researchers collected samples from 1,741 commercial cattle. The study started in feedlots, where intensively farmed cattle are moved after grazing. A feedlot consists of outdoor pens where cattle are fattened during their final months of life.

 Samples were also taken during slaughter and from market-ready products. No previous studies have tracked antimicrobial use and resistance right through the beef production process.

The team found no resistance genes to any bacteria in market-ready beef products. They did discover changes to antibiotic resistance genes in the guts of cattle during their time in the feedlot. The changes could be due to the use of antibiotics in feedlots but could also result from adjusting to a high-energy diet or from the cattle's maturation from adolescent to adult.