In Veterinary Medicine, antimicrobials play an important role in the maintenance of animal health, animal welfare and food safety. In short, the discovery of antimicrobial agents brought about a medical revolution. However, during the last decades, the continuing rapid development of antimicrobial resistance has emerged as a major global public health concern.
There has been no production of a new class of antibiotics in the last 3 decades; meanwhile these organisms are fast evolving to become resistant to the available ones. There is therefore a huge call on us to be more prudent in our utilization of antimicrobials as the consequences of inappropriate use, which are already becoming evident, are devastating.
What is Antimicrobial Resistance (AMR)?
Antimicrobial resistance is the ability of a microorganism to survive and grow in the presence of antimicrobial drugs. AMR becomes a problem when antimicrobials used to treat infectious diseases are no longer effective, leading to prolonged illnesses, disabilities and even death in both animals and humans.
Emergence and causes of AMR
AMR occurs when antimicrobials such as antibiotics, antifungal, antivirals and antihelminthics used to treat bacterial, fungal, viral and parasitic infections respectively are inappropriately used in animals and even humans. It is important to note that intrinsically resistant microbes are also found naturally in people, animals, food and the environment.
In animal husbandry, major facilitators of AMR include; use of antimicrobials as growth promoters in feeds and as prophylactics to prevent diseases in healthy animals. Aside their effects on animal health, these unwanted antimicrobial residues may be deposited in products of animal origins and animal tissues consumed by humans. They may also be released in animal wastes thus contaminating the soil, water and the environment in general. Land application of livestock manure as fertilizers also contributes to the introduction of resistant bacteria into the environment.
In healthcare, medical practitioners use incomplete or imperfect information to diagnose an infection and thus prescribe an antimicrobial just-in-case or prescribe a broad-spectrum antimicrobial when a specific one might be better.
Sometimes healthcare providers prescribe antimicrobials inappropriately wishing to placate an insistent patient who has a viral infection. This automatically presents a condition for the microbes to adapt.
These scenarios and many more contribute to the causes of antimicrobial resistance.
However, focusing only on the improper use of antimicrobials will be synonymous to fighting a battle midway; there is increasing evidence that medicines quality is another significant factor that contributes to antimicrobial resistance. Drugs with a lower composition of the active ingredients are said to lead to resistance.
Mechanisms of antimicrobial resistance
Antimicrobials fight germs but germs fight back and find new ways to survive (adapt). Their defense strategies are called resistance mechanism. Instructions for antimicrobial resistance are encoded in the chromosomal DNA (Deoxyribonucleic acid) of bacteria. Resistance genes are also found within plasmids (small, circular extrachromosomal DNA) which can transfer them from one bacterium to another.
There are two forms of resistance in bacteria.
The first, intrinsic resistance, is when a bacterial species is naturally resistant to a certain antibiotics or family of antibiotics, without the need for mutation or gain of further genes.
The other, acquired resistance, involves the acquisition of resistance by gene transfer or mutation.
- Vertical gene transfer: Transfer of resistance from parent organism to progeny
- Horizontal gene transfer: Transfer of resistance from one bacterium to the other. The resistance DNA can be acquired directly from the environment (transformation), through bacteriophage insertion (transduction) or by plasmid via cell-to-cell contact (conjugation)
- Mutation: Most microbes reproduce by dividing every few hours, allowing them to evolve rapidly and adapt quickly to new environmental conditions. During replication, mutations arise and some of these mutations may help an individual microbe survive exposure to an antimicrobial agent
Generally, the mechanisms by which bacteria resist antibiotics are:
1) Enzyme inactivation and modification
2) Modification of antibiotics target site
3) Overproduction of the target
4) Replacement of the target site
5) Selective exclusion via porins and efflux pumps
6) Reduced permeability
Roles of Veterinarians
In livestock production, veterinarians and farmers play a preponderant role when it comes to antimicrobial resistance. In many cases, veterinarians determine the appropriateness of antimicrobial usage in treatment, select the antimicrobials to be used, and also define the dosage and route of administration.
Veterinarians also provide valuable information to farmers on animal health, biosecurity and production management that can be used to identify risk factors associated with antimicrobial usage in livestock.
All these put veterinarians at the war front when it concerns antimicrobial usage and the transmission of resistant bacteria.
1) The concept of “One Health“: The fight against AMR requires an interdisciplinary approach. Reducing the dissemination and transmission of resistant bacteria within and between animals, humans and the environment is central when aiming to tackle AMR. The ability of bacteria to disseminate from one setting to another, sometimes over large geographic distances and among different populations makes it difficult to explain with certainty the origin of resistant bacteria strains. Therefore, the reservoirs and the transmission pathways of antimicrobial-resistance bacteria merit further investigation ideally through a One-Health Approach.
2) Research: Controlled experimental studies that assess the success of specific intervention are rarely conducted. This research area should be expanded to lay the foundations for the design and implementation of intervention strategies towards the reduction of AMR.
3) Data Collection: Data collection is an indispensable step in our attempt to understand and fight AMR. Monitoring of antimicrobial usage allows the analysis of temporal trend in antimicrobial consumption and can ensure compliance with prudent usage practice, programs or regulation.
4) Practice of good animal husbandry practices and biosecurity measures to prevent the need for any medicine in the first place. If animal production and transport conditions are improved, for instance by reducing stock density and stresses or by increasing hygiene and by introducing disease control techniques, then the actual need for growth promoters may be removed or decreased.
5) Usage of feed ingredients/additives that enhance the efficiency of feed conversion to substitute antibiotics as growth promoters (e.g in-feed enzymes, competitive exclusive products, probiotic, prebiotics, acidifiers, plants, extracts, nutraceuticals, essential oils, yeast and many others) and avoidance of feed ingredients with anti-nutritional properties (such as lectins and protease inhibitors).
6) Application of good practices for waste management, targeting primary production in specific value chains and highlighting practical actions that can be taken to reduce the need for antimicrobial and to control the dispersal of antimicrobials and resistant microbes in the environment.
Antimicrobial resistance is a complex phenomenon driven by biological processes and socio-economical factors that cannot be over-emphasized in the 21st century. Understanding the attitude and knowledge of everyone towards antimicrobial usage and its resistance is a crucial step for the design of strategies to combat this public health threat. In this combat, all medical expertise ranging from disciplines such as veterinarians, physicians, public health scientists, microbiologist, ecologists, epidemiologist and even students must be well equipped with knowledge that concerns the rightful use of antimicrobials.
By putting all hands on desk, we would not only be helping this generation but also the next to come.
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