A crucial issue
Antimicrobial resistance (AMR) spread is of major concern for human health and associated with growing economical issues. While it is increasingly hypothesized that wildlife could play an important role in antimicrobial-resistant bacteria (AMRB) dynamics, empirical data remain scarce at the moment. Nevertheless we felt that their exponential growth made a review worthwhile – to catch the major lessons that current results could bring. Therefore, we gathered evolutionary ecologists, microbiologists and veterinarians to investigate four questions: i) Which resistant bacteria are the most frequently observed in wildlife? ii) How are resistant bacteria exchanged between wildlife and the other compartments involved? iii) In which habitats are those resistant bacteria found? iv) Are resistances associated with some ecological traits of the host? To answer these questions we carried out a systematic search on the Web of Science and PubMed databases which allowed us to select 210 papers presenting data about antimicrobial resistant bacteria carried by wild animals.
Insights from the literature
Our work, published today in Journal of Applied Ecology, allowed us to infer some answers to our initial questions from the available data:
-The three main groups of bacteria found to be antimicrobial-resistant in wildlife are Escherichia coli, Salmonella spp. and Enterococcus spp. Yet the data we have concerning the AMRB found in wildlife are based on what has been searched for, meaning that we have information mostly on human pathogens.
-AMRB exchanges occur between wildlife, humans and domestic animals but the transmission routes are difficult to disentangle. Water seems to play a major role in those exchanges. Thus a critical way to control antimicrobial resistance spread may be to limit aquatic environment contamination by antimicrobial-resistant bacteria and antibiotics.
-The more habitats are impacted by human activities the more wildlife inhabiting them is impacted by AMRB. In other words the ecosystems that are the most anthropized are the ones in which the highest diversity of AMR is observed in bacteria carried by wildlife, including resistance mechanisms that are of major concern for human health.
-Omnivorous, anthropophilic and carnivorous species are at high risk of being potential carriers and potentially spreaders of AMRB, which means that diet and other ecological traits have to be considered to understand the role each species can play in AMRB spread.
Further research is urgently needed
This synthesis highlights both the important progress that has been made and the wide gaps that remain in our understanding of the role played by wildlife in AMRB dynamics. It is essential that authors give detailed data concerning the species they sample as well as describing focus habitats using comparable indexes. Such improvements seem necessary to move forward from successive studies that give information about one particular species in one particular habitat to comparable data that would allow broad comparisons. Moreover, data concerning AMRB prevalence in wildlife in developing countries are lacking, while AMR is of major concern in these regions, notably in South-East Asia. More attention should be paid in this area where the close links existing between wildlife, domestic animals and humans have proved to promote the emergence of pathogens. Similarly few studies have focused so far on wild fish while aquatic habitats appear to be highly impacted by AMRB contamination, notably due to the development of aquaculture. It is of major importance to focus on this group in future studies.
We sincerely believe that neither environmental reservoirs nor wildlife can be neglected if we are to meet the challenge of antimicrobial resistance control. Thus we hope that our work will help to raise the awareness of both microbiologists and ecologists and will encourage the development of multidisciplinary studies to tackle this issue.