A new report, Drivers, Dynamics and Epidemiology of Antimicrobial Resistance in Animal Production, released by the Food and Agricultural Organization (FAO) of the UN sought to track and assess elements involved in the spread of antibiotic resistance in animal production.
However, authors also highlighted that more research is needed to understand the issue and develop specific mitigation strategies.
“It is now accepted that increased antimicrobial resistance (AMR) in bacteria affecting humans and animals in recent decades is primarily influenced by an increase in usage of antimicrobials for a variety of purposes, including therapeutic and non-therapeutic uses in animal production,” said researchers in the report.
“Antimicrobial resistance is an ancient and naturally occurring phenomenon in bacteria. But the use of antimicrobial drugs – in health care, agriculture or industrial settings – exerts a selection pressure which can favor the survival of resistant strains (or genes) over susceptible ones, leading to a relative increase in resistant bacteria within microbial communities.”
Recommendations to reduce the spread included improving hygiene and biosecurity in animal production and data collection to better understand aspects of the process and elements involved.
Pressure from animal antibiotic use
There is evidence to support the view that in-feed usage of antimicrobials in animal production has established antimicrobial resistant bacteria in livestock and is connected to the AMR bacterial populations in humans, said the researchers. “In animal production, the prolonged use of antimicrobial growth promoters (AGPs) at sub-therapeutic levels in large groups of livestock is known to encourage resistance emergence, and is still common practice in many countries today,” they added.
However, they said, there have been studies that point the emergence of AMR in bacteria in humans to human use of antimicrobials.
“Excessive use and misuse of antimicrobials are widely recognized as two of the major drivers for acquired AMR, both directly and indirectly, due to the selection pressure imposed on human and animal microbiota, and on environmental bacteria,” they said.
Intensive animal production systems may lead to the spread of bacteria resistant to antibiotics among animals, especially if biosecurity practices are inadequate, they said.
Additionally, aquaculture production may see the development of antibiotic resistant bacteria, they said. “The extent and persistence of antimicrobial residues in aquatic systems is unknown and current evidence is conflicting,” they added.
As there are no maximum limits for antimicrobial residue in water, it can be a vehicle that carries both antimicrobial residues and resistant bacteria, the researchers said.
Mitigation efforts
If pressure from the use of antimicrobials in animals were removed it would likely not end the global growth of antimicrobial resistance, said the authors. AMR genes have the ability to move between bacteria and other hosts.
“However, the release of large quantities of antimicrobials or resistant bacteria into the environment is still thought to be an important point for control, and therefore measures which encourage the prudent use of antimicrobials are likely to be extremely useful in reducing the emergence and spread of AMR,” they said.
The researchers also pointed to other efforts to reduce pressure on antimicrobial use and resistance spread. These included developing biodegradable antimicrobials, improved hygiene and biosecurity in animal production and water treatment, they said.
“Intensive livestock production methods should be improved by identifying the most efficient systems with regards to minimizing environmental contamination with antimicrobial residues and resistant pathogens, taking into account local conditions and needs, and ensuring sustainability,” they said. “The benefits of better feed, water, biosecurity and management standards need to be assessed.”
Future research
There is room for data collection and better understanding regarding the spread of AMR and transmission pathways from animal production and humans, said the researchers.
“The relationships between different types of farming systems and both AMU [antimicrobial use] and the emergence and spread of AMR are discussed in this paper, including extensive and organic systems, but there is still a notable lack of knowledge on the role that sustainable agriculture systems can play in combating AMR,” they said.
“Most importantly, future research needs to involve an interdisciplinary (e.g. One Health) approach, integrating agricultural, medical, environmental and social sciences, and especially recognizing the importance of human behavior."
Among the topics that need be addressed with additional data collection and research are establishing a database of resistance genes; examining the interaction of antimicrobial and microbial populations to improve treatment and reduce AMR risks; tracking the connection between AMR in livestock and resistant infections in human; and examining wildlife species as potential carriers, they said.
“Surveillance for AMR should include more emphasis on epigenetics (using molecular techniques and bioinformatics) to allow tracing the origin of emergence,” added the authors.