May 31, 2020

What role does agriculture have in the transmission of antibiotic resistance?

the rise of antibiotic resistance in pathogenic bacteria It has become a major health problem worldwide, as it reduces the therapeutic efficacy of antibiotics.

Although this phenomenon has occurred naturally since ancient times, it has become much more frequent in recent decades. The main causes are the excessive or inappropriate use of antimicrobials and their greater presence and permanence in the environment.

The spread of antibiotics in the natural environment is mainly associated with their application in medicine and veterinary medicine.

However, the role that agriculture, as the basis of the food chain, may play in the transmission of antibiotics, antibiotic resistant bacteria and antibiotic resistance genes through food has not been adequately considered. We could be undervaluing it.

How do antibiotics get to the field?

In the Anglo-Saxon area, the term agriculture includes crop production, but also livestock and aquaculture, which constitute the main entry of antibiotics into the agricultural system.

It is estimated that the amount of antibiotics used in crop protection represents less than 0.5% of the total employed in animal production. This excludes Europe, where its application in crops is prohibited.

However, the use of animal manure, organic waste or sewage sludge as fertilizer material is increasingly common. This material may contain a high load of antibiotics.

Some studies confirm that between 30 and 90% of antibiotics used in animals appear in the droppings. Contaminated manure exposes crops, including organic ones, to the presence of antibiotics.

This, together with the use of wastewater in irrigation, causes these agro-ecosystems to be repeatedly exposed, and for long periods of time, to the presence of a considerable and varied load of antibiotics.

These agents can be taken by plants and cause phytotoxic effects that affect the germination and growth of different agricultural crops. In addition, they can accumulate in plant tissues and pose a potential risk to human health, as plants are the first link in the food chain.

This risk has been taken into account only in the last two decades and, therefore, information about its impact It is limited.

Resistance to antibiotics used in people detected in EU animals

Effects of antibiotics on plants

Recent studies they have shown that the phytotoxicity of antibiotics in crops depends largely on the plant species and the type of antibiotic, as well as its concentration in the soil.

However, most of the phytotoxic studies of antibiotics have been performed. in vitro. Field studies are scarce. While is true that Have been observed negative effects with high concentrations, at low concentrations a stimulatory effect has been detected.

In addition to the direct impact of antibiotics on plant growth, they can indirectly cause alterations in the soil microbiota. This affects their diversity and the presence of beneficial bacteria for culture such as N fijado fixing bacteria, which can also affect crop yield.

What to do from now on?

Plants can come into contact with antibiotics in two ways:

  • Direct receivers. When antibiotics are applied to control bacterial diseases.
  • Indirect receivers. For the application of organic amendments, sewage sludge or sewage.

As a consequence, their growth can suffer direct and indirect negative effects, due to the modification of soil microorganisms with which they interact. In addition, they can act as transmitters of both antibiotics and resistance, since they are the basis of the food chain.

Therefore, it is necessary to monitor, quantify and minimize the degree of antibiotic contamination of organic contributions or amendments and of the water that is applied to crops.

Although various treatments have been used such as composting or the conversion into biochar (charcoal) to reduce the amount of antibiotics and by-products present in manure, 100% elimination has not yet been achieved.

This is because the efficiency of the process depends on multiple factors (starting material, microorganisms present, temperature, time, type of antibiotics present …). Therefore, new studies and technological improvements are still needed to achieve a total elimination of antibiotics that are applied through organic amendments in crops.

At the same time, it is necessary to investigate in depth how antibiotics enter the plants, their transformation and / or accumulation in the different plant organs and their persistence in them. Above all, of those who are going to be used for food, whether animal or human.

These studies will help reduce its potential risk to people's health. In addition, taking into account that these fertilization and irrigation systems are carried out repeatedly every year, it is important to carry out systematic long-term analyzes.

This article constitutes a summary of the talk given in the UPV / EHU summer course organized by the JRL Environmental Antibiotic Resistence, to which the authors belong.

This article was originally published in The Conversation. You can read the original here.

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