What is an antimicrobial agent?

“Antimicrobial”, a broad term defining even antibiotics, means whatever substance of natural, semi-synthetic or synthetic origin that in vivo concentration kills microorganisms or inhibits their growth or multiplication.

Antimicrobials are one of the most important therapeutic discoveries in medical history. Since the introduction of penicillin in the 40s, antimicrobials have played a key role in treating numerous microbial infections in humans and animals, improving significantly public health, animal welfare and health and ensuring high standards of production of food of animal origin.

Unfortunately, 70 years later, their improper and/or non-rational use is representing a serious threat to global public health due to the selection and spread of antimicrobial resistant microorganisms.

This phenomenon is called antimicrobial resistance.

What is antimicrobial resistance?

Antimicrobial resistance is the ability of a microorganism to resist the action of an antimicrobial agent. Antimicrobial resistance is a European and global health problem, increasingly serious to humans and animals, limiting or making treatment options less effective and decreasing the quality of life at the same time. Moreover, it leads to severe economic consequences in terms of rising healthcare costs and loss of productivity.

In the European Union, 25 000 deaths from infections caused by antimicrobial resistant bacteria are estimated annually.

Such infections result in additional healthcare costs and loss of productivity of at least 1,5 billion Euros per year. At this rate, it is assumed that, globally, the number of people prematurely dead because of antimicrobial resistance will be 300 million over the next 35 years.

(Please consult document AMR: a major European and Global challenge)

Antimicrobial resistance is the biological natural adaptation of certain microorganisms that gain the ability to survive or to grow in the presence of an antimicrobial concentration that is generally sufficient to inhibit or kill microorganisms of the same species. 

When this is due to the nature of the microorganism itself, it is called intrinsic resistance. In this case, the microorganism concerned has never been sensitive to a particular antimicrobial agent.

In other cases, bacterial strains previously susceptible to a particular antimicrobial agent develop resistance. This is called acquired resistance.

The ability to resist can be achieved through genetic mutations or the acquisition by other organisms of resistance genes already “pre-built”.

How does it develop?

Acquired resistance develops by means of natural selection. Since bacteria can reproduce very rapidly – they can grow and reproduce in just 20 minutes – and considering the huge number of microbes in the environment, antimicrobial resistance can develop relatively quickly.

Acquired antimicrobial resistance can develop:

  • spontaneously from a random mutation in the genetic material of the microorganism that makes it resistant to a certain type of antimicrobial. In this case, in the presence of the substance, sensitive bacteria do not grow, while the resistant “mutants” actually grow and multiply and are transmissible to other animals and/or humans;
  • by acquisition of resistance genes directly from other microbes. The bacterium transmitting the resistance gene does not need to be a pathogen. Therefore, a non-pathogenic organism can develop resistance and then transmit it to a pathogenic one. This is particularly important in bacteria. These resistance genes are present on pieces of DNA, which can be transferred between the different bacteria and are known collectively as “mobile genetic elements”. These mobile genetic elements often include clusters (groups) of genes containing even multiple resistance factors, giving the recipient microorganism multiple resistance characteristics, which means at least three or more classes of antimicrobials.  

Why is it a problem?

Resistant pathogenic bacteria do not necessarily provoke severe diseases than the more sensitive ones. However, the disease gets more difficult to be treated because only a reduced range of antimicrobials will be effective. This leads to a longer course or a more serious disease, which in some cases leads to death.

The progression of antimicrobial resistance can be accelerated by the excessive and/or inappropriate use of antimicrobials that, in addition to a poor hygiene or deficiencies in the prevention and control of infections, creates favorable conditions for the development, spread and persistence of resistant microorganisms in both humans and animals.

The extent to which the use of antimicrobials in the veterinary sector poses a risk for man arising from antimicrobial resistance requires more investigation. In fact, the mechanism by which the resistance can be transferred to humans and the extent of the threat to human health are still unclear.

Nevertheless, we cannot deny that there is a need to limit the spread of antimicrobial resistance in certain animal pathogens and zoonotic agents present in animals and food through an appropriate control of the use of antimicrobials in the veterinary field.

Please consult Biosafety and correct and rational use of antibiotics in zootechnics.

Data di pubblicazione: 19 gennaio 2017, ultimo aggiornamento 19 gennaio 2017

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