Not a one-way street: Antibiotic resistance genes found on cattle farms suggest spread from humans to livestock

The first study to track antibiotic resistance all the way through the intensive beef production process found genes conferring resistance to ‘last resort’ antibiotics (carbapenems) which are not used in the livestock industry. The authors, publishing in eLife, say their finding provides evidence that antibiotic resistance can spread through the environment from human to agricultural settings. The researchers were also surprised to find a lack of resistance genes in market-ready products, suggesting safety measures to stop resistant bacteria entering the food chain were effective. 

 

Dr. Adina Howe, Assistant Professor, Agricultural and Biosystems Engineering, Iowa State University (webpage):

Expertise: Identifying microbial drivers of global change; biological indicators of environmental health; interactions within complex microbial communities.

“We are increasingly aware that antibiotic resistant genes are widespread in the environment but know very little about their persistence and spread.  This study is an exciting effort that fills an important gap in our knowledge by surveying the presence of antibiotic resistant genes in interconnected beef production environments.  Though two feed lots are far from being representational for beef production, or more broadly our ‘food chain’, this study demonstrates the value of collecting this data, and more importantly, offers direct benefit to the field by making it available in an open-access research publication.  

“This research supports previous efforts that make us increasingly aware and concerned about the presence of carbapenem resistant genes, as well as other antibiotic resistant genes, in human and agricultural environments. However, the identification of these genes is only an initial step in understanding how resistance genes impact our health, and we still know very little about how these genes move in the environment, how long they persist, and how they may spread, especially into clinical settings.

“A limitation to this study is that the authors quantify the potential of antibiotic resistance rather than observed functional resistance.  For example, the microbes identified to contain genes-associated with carbapenem resistance have the potential to be resistant to the antibiotic, but additional tests would be necessary to demonstrate actual functional resistance.  Also, genes present at low abundance in environmental samples would be difficult to sample with the approaches used in this study, and low abundance genes could possibly persist and spread.  Nonetheless, the data provided is critically needed to help narrow down numerous possible control points where researchers might focus future research efforts to address these limitations.”

 

Dr. Jeffrey LeJeune, Professor and Head of the Food Animal Health Research Program, Ohio State University (webpage):

Expertise: Pre-slaughter control of human foodborne pathogens and antimicrobial resistant bacteria in the animal host and the environment.

“The authors exploit novel approaches to explore presence of antimicrobial resistant genetic elements in beef feedlot systems.  These tools may help to shed some light on the ecology of antimicrobial resistant bacteria in food systems.  It would be of great interest to know how much the complexity of antibiotic resistant genes in bacteria described in this study resembles other agricultural, urban, or pristine environments.  That is to say, how much does having cattle in this environment contribute to the complexity reported?   Were the changes over time due to chance alone, seasonal variation, or some other factor such as animal age, diet, or other unmeasured management factors?

“The authors acknowledge a number of limitations. For example, the unexpected absence of resistance organisms in meat products could be attributed to the methods employed that may decrease sensitivity to detect bacterial DNA in those samples. Notwithstanding, this study adds to our understanding of the distribution of antimicrobial resistant genes in bacteria in feedlot production systems. Over eighty years ago, the Dutch microbiologist, Bass-Becking, proposed that ‘Everything is everywhere, but the environment selects.’ Maybe now we have the tools for testing this hypothesis.”

 

Declared interests (see GENeS register of interests policy):

No interests declared

 

Reference:

Resistome diversity in cattle and the environment decreases during beef production’ by Noyes et al., published in eLife on Tuesday 8 March, 2016.

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