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Review
. 2015 Mar;8(3):240-7.
doi: 10.1111/eva.12185. Epub 2014 Aug 2.

Antibiotics in agriculture and the risk to human health: how worried should we be?

Qiuzhi Chang  1 , Weike Wang  1 , Gili Regev-Yochay  2 , Marc Lipsitch  1 , William P Hanage  1
Affiliations
Review

Antibiotics in agriculture and the risk to human health: how worried should we be?

Qiuzhi Chang et al. Evol Appl. 2015 Mar.

Abstract

The use of antibiotics in agriculture is routinely described as a major contributor to the clinical problem of resistant disease in human medicine. While a link is plausible, there are no data conclusively showing the magnitude of the threat emerging from agriculture. Here, we define the potential mechanisms by which agricultural antibiotic use could lead to human disease and use case studies to critically assess the potential risk from each. The three mechanisms considered are as follows 1: direct infection with resistant bacteria from an animal source, 2: breaches in the species barrier followed by sustained transmission in humans of resistant strains arising in livestock, and 3: transfer of resistance genes from agriculture into human pathogens. Of these, mechanism 1 is the most readily estimated, while significant is small in comparison with the overall burden of resistant disease. Several cases of mechanism 2 are known, and we discuss the likely livestock origins of resistant clones of Staphylococcus aureus and Enterococcus faecium, but while it is easy to show relatedness the direction of transmission is hard to assess in robust fashion. More difficult yet to study is the contribution of mechanism 3, which may be the most important of all.

Keywords: Enterococcus; Staphylococcus aureus; agriculture; antibiotic resistance; food; resistance transfer.

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Figures

Figure 1
Figure 1
Schematic illustration of possible links between antibiotic use in agriculture and human disease. The prevalence of resistant bacteria in agriculture is influenced by antibiotic use in that setting. The impact of infection depends crucially on the capacity for sustained human to human (H2H) transmission. Arrows linking the two populations represent: a) direct transmission of bacteria not adapted to transmission in humans via the food chain (e.g Campylobacter, Salmonella) or direct contact with animals; b) direct transmission of organisms already adapted to transmission in humans; c) transfer of resistance genes from the agricultural setting into pathogens transmitting among humans.
See this image and copyright information in PMC

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