AMRflows: antimicrobials and resistance from manufacturing flows to people: joined up experiments, mathematical modelling and risk analysis

Antibiotics and other pharmaceuticals are released into rivers from multiple manufacturing sites at concentrations high enough to select for antibiotic resistance genes (ARGs). Such mixtures of antibiotics may select for new combinations of resistance genes, which is particularly concerning as this will further limit antibiotic treatment options. In addition, bacteria from treating manufacturing waste or domestic sewage and raw sewage entering rivers will mingle, facilitating horizontal gene transfer (HGT) of resistance genes carried on plasmids. However, the antibiotics will be diluted while being transported downstream, and some will be quickly degraded, and resistant bacteria may not survive so the question is how long is resistance selected and how long does it survive? Is resistance transmitted to other bacteria before they are lost? How far are resistant bacteria transport and what is the exposure of humans or livestock?

In order to ask these questions, evaluate mitigation strategies and develop evidence-based global environmental standards, we will pursue a unique combined experimental and mathematical modelling programme including the following streams:

(1) Measure concentrations of antibiotics and heavy metals, water chemistry, water levels and flow rates, water sediment exchange, abundance and diversity of antibiotic resistance genes and antibiotic-resistant bacteria.
(2) Quantify transmission of resistance genes in bench-scale reactors.
(3) Study selection in the river samples in bench-scale reactors under realistic, controlled conditions.
(4) Study the risk of infection by resistant bacteria in tissue culture and Zebrafish laboratory models and the antibiotic dose required for treatment.
(5) Build and test a mathematical model of antimicrobial resistance (AMR) dynamics on the small scale of a water sample, including degradation of antibiotics, growth and death of sensitive and resistant bacteria, selection of resistance as a function of antibiotic concentration, HGT of resistance.
(6) Build and test a model of water flow for the river network; this will be on the large scale of rivers.
(7) Combine the small-scale AMR dynamics and large-scale transport models into a model that can calculate the dilution of the compounds and track how long the chemicals and bacteria have been in the river water, sediments and floodplains and how far they spread to downstream populations and ecosystems.

The combined model can evaluate whether interventions such as separate treatment of antibiotic manufacturing waste and domestic sewage would be effective in reducing resistance levels before putting this into practice.

The environmental AMR pathways will be examined across two river systems. The Musi (Hyderabad) is more polluted with antibiotics than the Adyar (Chennai). Both are polluted by sewage. Their pollution flows to people via irrigation, drinking water production and spiritual cleansing. These rivers have phases of low flow with concentrated industrial waste and sewage and limited bacterial spread and high flows in the monsoon season, flooding communities with resistant bacteria.

(8) Analyse the human health risks based on the predictions of the combined model and the experimental study in (4) and other information. The risk analysis will include the level of uncertainty in those risks and will contribute to the development of international environmental standards.

These will be the two main outcomes to improve human, animal and environmental health, specifically (i) quantitative evidence for resistance (co)selection and transfer under in situ conditions in a more and less polluted river system and (ii) a truly novel combined AMR dynamics and transport modelling framework that can be used globally as a tool to track AMRflows.

Antibiotics have been saving millions of lives, and lack of access to antibiotics in LMICs is a major problem. Nevertheless, the rise of pathogens resistant to antibiotics due to prudent but mainly less prudent use of antibiotics means that many infections cannot be cured anymore by antibiotic treatment. The problem is global, as any emerging resistant bacteria are quickly transported across Earth.

A particular concern are antibiotic production facilities that release antibiotics into the environment at concentrations so high that selection for resistance occurs. We need to understand how big this problem is, how far the antibiotics travel before their concentrations are too low to select and how far the resistant bacteria travel and how long they will survive once the selection pressure has faded. Further, we need to know which levels of pollution pose no risks to animal and human health so we can set appropriate standards. Also we need to know how best to intervene, should the antibiotic waste be treated on site, or diluted and mixed into rivers or domestic sewage treatment plants? Should antibiotics best be massively diluted upon discharge?

Our project will make important contributions to address these issues and questions. Our impact goals are to:

- contribute to risk assessment and setting evidence-based environmental standards
- evaluate the effect of changes in wastewater treatment and effluent release on AMR exposure and recommend changes in practise if these are advisable

The key beneficiary communities will be:

- government agencies regulating pharmaceutical production facilities
- pharmaceutical companies selling antibiotics as they will more quickly become ineffective if pollution increases resistance
- water industry responsible for treating sewage and producing drinking water
- patients having to undergo antibiotic therapy

We will work to ensure that our evidence is disseminated to the stakeholders, who if public pressure is strong enough will take action. For this reason, it is also important that the public is kept informed of our results.

We will measure impact ultimately by changes in regulations and changes in practice.