Does the potential for AMR selection differ between common UK cattle grazing systems?

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Antimicrobial resistance (AMR) occurs because repeated exposure to antimicrobial drugs kills susceptible bacteria leaving the resistant types to multiply. Recent high-profile reports of the devastating consequences for human health caused by the resistance of disease-causing bacteria to antibiotics have emphasized the need to understand the processes that drive increasing prevalence of antimicrobial resistance in human and animal pathogens.Farm animals are considered to be a major source of AMR because of the large amounts of antibiotics used both to treat infection (therapeutic use) and to prevent infection (prophylactic use). However, little is known about the background levels of resistance in farming systems, even when animals are only treated with antibiotics when they need them (therapeutically). For instance, the sharing of genetic material by bacteria that are in close proximity is another route where AMR may emerge unexpectedly in otherwise non-related bacteria. AMR transmission between cattle is likely to be greater when they are close together, for example during the winter housed period. In this proposal we will use an experimental farm where cattle being raised for beef production only receive minimal antibiotic treatment described as 'best practice' by vets. We will monitor dynamics of AMR bacteria and genes in cattle dung in summer when the cattle are grazing in the field, and in the winter when they are housed together. We will carefully monitor cattle who have been sick and have been given antibiotics and those in the rest of the herd.The diet of farm animals may also effect increased AMR in their gut flora. Even common plants ('forage') like grass and clover that cattle commonly eat when they are out grazing produce natural antimicrobial compounds that may continue to be active in the stomach (rumen) where millions of bacteria thrive and multiply. In the winter, cattle are brought indoors and fed silage which is grassland plants that have been fermented to conserve them. Undigested diet and lots of bacteria from the rumen, and therefore perhaps AMR, are excreted in cow dung. We will analyse the dung of cattle that eat different forage types to find out if what they eat affects the likelihood of AMR arising in cattle fed one diet compared to another.Most cattle farming in the UK is situated in the hilly 'wet West' where the potential for rain to runoff fields into waterways is high. Recent increases in storms that cause lots of runoff and flooding may be due to climate change, are predicted to continue. At the same time, in recent years there has been an increasing recognition that AMR may arise in farm animals and be released from the farm environment to the natural environment in water and might therefore end up in drinking water, bathing water or in seafood. Normally, pollution from cattle dung in water is monitored using faecal indicator organisms (FIOs), which are bacteria that do not usually cause disease but which correlate with those that do (pathogens), and can be handled safely by scientists. It would be useful to know what proportion of FIOs carry AMR, because they are routinely tested for, facilitating estimates of AMR transmission to be estimated in the future. We will sample water flowing from fields that have been grazed by beef cattle or spread with their manure, and analyse the bacteria in the water including the FIOs to see if they are resistant to antibiotics.The results of this study should help us to understand whether AMR that arises in cattle herds may be transferred to the environment, whether management can limit AMR and its transport, and inform approaches for assessing risks of new antibiotics and managing adverse effects that might be occurring. It is important work for addressing risk in our complex agro-food system that is clearly important for both consumers and farmers.