The natural environment is contributing to AMR

Bacteria and other microorganisms produce and excrete a range of bioactive compounds; some may be beneficial to surrounding microbial communities, enhancing symbiotic relationships; some may be innocuous; and others may be detrimental. As a way of protecting themselves from harmful compounds, many bacteria will develop resistance mechanisms and in turn produce their own antimicrobials. In this way, the production of antimicrobial compounds and the subsequent development of antimicrobial resistance (AMR) is natural and intrinsic to many microbes.

We recognise overuse of antibiotics as being the major cause of AMR in bacteria; however, in the recently published Frontiers 2017 report, the United Nations (UN) has identified the role of the environment in antimicrobial resistance as an emerging global issue.¹

The natural environment is contributing to AMR

Our use of antimicrobials in human and animal health, and more significantly in agriculture, has resulted in antibiotic compounds and residues being deposited in the environment. The flow-on effects are a substantial increase in the selection pressure for environmental bacteria to acquire AMR.

Exposure of human populations to resistance genes and environmental microbes can occur through contact with soil and water, including drinking water, and through the food chain. Sources include municipal wastewater, hospitals, pharmaceutical production facilities and even household waste.

The UN report suggests that these could be new sources from which humans could acquire AMR infections. The concern is that previously harmless bacteria could become a reservoir for AMR genes, with the potential for human pathogens to acquire these genes.

Co-selection drives AMR resistance Prescription and agricultural antibiotics are not the sole source of the increasing AMR compounds in the environment; other antimicrobial compounds, including disinfectants, biocides and heavy metals, can elicit resistance in environmental microorganisms.

And these AMR compounds don’t always work solo – co-selection is a major driver of bacteria acquiring AMR genes. Exposure of environmental microbes to mixtures of antibiotic residues and other pollutants can not only increase selection pressure compared with a single compound, but also select for resistance against multiple antimicrobials.

Heavy metals are also a particular problem because the mechanism of antimicrobial action and resistance is very similar to antibiotics, so in the presence of excess heavy metals, microbes may develop partial resistance to antimicrobials they may not yet have encountered. Moreover, heavy metals are ubiquitous in the environment, which means microbial communities are ‘primed’ for resistance.

Wastewater is a reservoir for AMR bacteria

Untreated wastewater, such as pharmaceutical effluent, agricultural run-off, animal manure and abattoir waste, contains AMR compounds and/or bacteria and discharging these wastewaters without treatment is thought to be a major driver of the development of AMR in the environment. Wastewater treatment facilities are not typically designed to inactivate antimicrobial compounds, although the concentrations of AMR compounds released from wastewater effluents into the environment are generally low, 1000-fold lower than clinical levels. Antimicrobials in treated effluent may be inactivated with soil adsorption and those that remain active can exert section pressure on surrounding environmental bacteria. Moreover, the low concentration of AMR compounds in the environment is a particular problem – it’s not high enough to kill surrounding bacteria, but is sufficient to select for resistance.

We know it’s bad, but do we know enough?

The conundrum is that before we act, we need to make evidence- based decisions – but do we have enough evidence? And do we have time to gather more data? By then, it might be too late to implement any meaningful solutions.

But here’s what we do know: wherever there is human activity, the emergence of AMR occurs at an increased rate. We know that there is an increased risk of food- and environmental pollutant- borne AMR transmission. And we know if we don’t act now, our window of opportunity for action may be lost for good.

Taking the first steps

Tackling this emerging problem will require a massive, globally coordinated effort. We need to take an approach of implementing measures to control/reduce the amount of antibiotics released into the environment, based on sound evidence, alongside ongoing research.

According to the UN, current measures in addressing this problem include:

  • voluntary initiatives by drug manufacturers to reduce the level of antibiotics  in discharged  effluent (see article on page N13)
  • restriction of specific co-selecting compounds from consumer products
  • antibiotic compounds that have potential to cause damage to marine ecosystems being put on the European Union Watch List of emerging pollutants
  • improving the removal of antimicrobial residues from secondary and tertiary wastewaters treating animal waste before land use.

The effects of antimicrobial disposal on the environment and its role in driving AMR resistance in environmental microorganisms is now at the forefront of the global AMR issue. Recognising this as a major contributing  factor and taking action are much needed weapons in the fight against AMR.

Nidhi Sodhi
Science Writer

This article appeared in the Australian Veterinary Journal: Aust Vet J 2018;96(3):N5

Reference

  1. United Nations Environment  Programme.  Antimicrobial  resistance: investigating the environmental dimension. In:  Frontiers  2017 Emerging Issues  of Environmental  Concern. UNEP,  Nairobi,  2017;12–22. https://www.unenvironment.org/resources/frontiers-2017-emerging-issues-e.... Accessed December 2017.

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