The Lancet, Animal Agriculture and Antibiotic Awareness Week


The Lancet Infectious Diseases published an editorial entitled Antibiotic resistance—the need for global solutions to mark Antibiotic Awareness Week (which is this week, FYI). The article is as long as the situation is complicated. With twenty-six contributors and nearly 400 references, it looks to address the concerns around antibiotic resistance, factors that cause resistance, and recommended strategies to maintain/ensure continued efficacy of antibiotics.  Though I will focus on the issues around agricultural antibiotic use, the journal article covered the interaction of multiple industries, including the often overly judicial prescription of antibiotics in human medicine.  The editorial was written by experts in many fields, and is sensitive to the controversy surrounding antibiotics in agriculture.  It addresses the need to “move on from blame and shame” and instead urges us to realize that the growing threat of antimicrobial resistance is an issue with incredible complexity, requiring collaboration.

What is antibiotic resistance?

Antibiotics are a group of antimicrobials that kill or inhibit the growth of microogranisms, specifically bacteria. They are incredibly important in both human and animal health, providing treatment to illnesses caused by bacterial infection and as a prophylactic (for example: in surgical situations, where risk of bacterial infection is increased). In agriculture, antibiotics are used to treat sick animals, increase feed-efficiency, prevent infection and improve animal welfare. When bacteria survive exposure to a given antibiotic, they are considered resistant. You’ve heard the term “superbug?” Quite simply, this is a bacteria that is resistant to more than one drug.

How is resistance formed?

Resistance can be a result of a bacterium acquiring resistant genes from another pathogen through horizontal gene transfer, or a result of a genetic mutation. When pressure is placed on a population over time, that population will evolve. In this case, when we put selection pressure on bacteria by exposing them to antibiotics, we inadvertently select for those bacteria that will survive (those that are resistant).

Selection pressure worsens in certain circumstances, like exposing bacteria to mild doses of antibiotics over long periods of time, exposing populations to a portion of the dosage required to kill them, using antibiotics when they’re not necessary (not because selection pressure is increased, but because it is unnecessary) and targeting a bacteria with the antibiotic it is already resistant to.

How is resistance in animals related to resistance in people?

An infectious agent that can transfer between humans and animals is referred to as zoonotic, and includes many species of bacteria. In these cases, the concern for resistance is pretty straight forward. A bacterial population that develops resistance in one species has the potential to infect the other and, with selection pressure, continue to develop resistance(s), with fewer and fewer options for control.

“The interface between human beings and animals is complex,” explains the editorial, “numerous possible pathways exist for transmission of resistant bacteria.”

There are many stages along the production line, for example, where bacterial contamination can occur and/or populations can change.

Read more: XL Foods and E. coli

For those bacteria that don’t transfer between species, the concerns are far more complicated, but according to the paper, “strong circumstantial evidence suggests that resistance genes circulate between people, animals, and the environment.”

One such concern? Horizontal gene transfer between pathogens can result in the movement of resistant genes from one species of bacteria to another. So it’s not as simple as assuming a non-zoonotic, resistant species will pose no risk to the health of another species.

What role is agricultural antibiotic use playing?

I guess this is where the controversy develops. Many refute the use of non-theuraputic antimicrobials, as they increase selection pressure on resistant strains. Others explain that agricultural antibiotic use has little impact on antimibiotic resistance concerns in human health, because ionophores (the primary antibiotics used) are not used in human health.

Watch Beef Research School: Antimicrobial Resistance Management in Livestock Production

What is the potential effect of antibiotic resistance on the human population? Livestock industry?

Antimicrobial resistance could have huge ramifications on human health, best summarized by “longer duration of illness and higher rates of mortality in patients with resistant infections, increasing costs of treatment for resistant infections, and inability to do procedures that rely on effective antibiotics to prevent infection,” according to the Lancet’s article.

In the livestock sector, it would likely result in many of the same problems, and, potentially, the increased use of antibiotics also used in humans, putting further selection pressure on resistance.

What are potential solutions?

The paper suggests a myriad of approaches, including (but not limited to):

  1. New antibiotics – Putting a new focus on the potential for narrow-spectrum, natural and/or organism-specific drugs may be key in reducing resistant populations. Narrow-spectrum, or organism-specific drugs would mean resistance would be less likely to develop in non-target populations. Also, the higher the variety of antimicrobials, the less selection pressure in bacterial resistance.
  2. Adjuvants – An adjuvant is an agent that modifies the effect of other compounds — in this case to potentiate the work of antimicrobials. Such compounds could work in many different ways, like either increasing the susceptibility of a bacteria to a given antibiotic, or interfering with the mechanism that makes a bacteria resistant.
  3. Antivirulence Strategies –  This would employ compounds that do not kill the bacteria, but instead destroy their ability to infect. Work still needs to be done to further understand this technology and its application in humans, but some initial results are promising, and could prove affective in targeting populations with antibiotic resistance.

And specific to the livestock sector?

The editorial suggests: “a global code of conduct should be developed for antibiotic use and implementation of strategies against antibiotic resistance,” with phasing out of unnecessary antibiotic use and monitoring/control of antibiotics in the environment.

A global code of conduct would mean no country has an advantage over another, and there would be fewer trade barriers. In terms of antibiotic use — the above suggests halting unnecessary antibiotic use (e.g. non-therapeutic). The editorial does not seek to abolish prescribed antibiotic use in the livestock sector, nor in human health, asking only that they be used responsibly, to prevent further resistance problems.

What do you think?

If animal agriculture looks at improving all other aspects of the operation, is it reasonable to consider reducing reliance on antibiotics? With ever-increasing trade opportunities and expanding markets, will we slowly move towards this change based solely on demand criteria? Or would such change require political intervention?

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