Antimicrobials are medicines used to kill micro-organisms or to stop them from growing and multiplying. They include antibacterial medicines (i.e. antibiotics), but also medicines against viruses (antivirals), against molds (antifungals) and against parasites (antiparasitics).

Antibiotics are the most commonly used type of antimicrobials, most often in human and veterinary medicine to treat a wide variety of infections, and to a lesser extent in horticulture. Antimicrobials against one type of micro-organisms are not effective against other types. For instance, antibiotics kill bacteria, but they won’t work against viruses. Therefore, antibiotics will not cure viral infections such as colds, most coughs, many types of sore throat, and influenza (flu).

An antimicrobial resistant micro-organism is not susceptible to at least 1 antimicrobial, either by change of its genome (‘adaptive resistance’) or by its intrinsic features, such as a thick and protective cell membrane.  
In other words, antimicrobial resistance can be either acquired or naturally present in a specific type of micro-organism. Although both can be involved in therapy failure, acquired resistance is to blame for most recent cases. Acquired resistance can be induced by inappropriate use of antimicrobials (for example prescription of antibiotics to treat viral infections or unnecessary long treatment duration).

Micro-organisms, and especially bacteria, are naturally present within our body, in animals and in the environment. Only a tiny fraction of all known bacteria, some 10–20 species such as Mycobacterium tuberculosis or Streptococcus pneumoniae, are specific human pathogens. Our bodies are host to hundreds of other species that form different communities with other microbes: cutaneous microbiota, gut microbiota, vaginal microbiota, pulmonary microbiota, etc. 
Most of them play a beneficial role and protect us against dangerous infections, but when the immune system is weakened or when microorganisms enter the body by an unusual route, some can become pathogens (i.e. agents responsible for diseases) and cause infections. For example: the bacterium Escherichia coli is naturally present in the gut, but can cause for instance a bladder infection (cystitis) if passing from the rectum into the urinary tract. 

Administering antimicrobials to treat an infection (i.e. when micro-organisms are exposed to antimicrobials), kills sensitive micro-organisms. This leaves space for resistant strains to thrive and multiply and, as a consequence, oust their sensitive counterparts. Some micro-organisms, initially sensitive to antimicrobials, can when exposed to antimicrobials mutate or acquire mobile resistant genes from other micro-organisms (e.g. commensal flora) and become resistant. This is called acquired antimicrobial resistance. Resistance develops gradually when potentially harmful bacteria acquire the capability to reduce or eliminate the effectiveness of one or more antimicrobial substances. Other bacteria are intrinsically resistant to certain types of antimicrobials, because their target is missing or out of reach for the drug. 

In the fungal world, resistance can be obtained during antifungal therapy but may also develop in the environment (link is external). This is the case for the saprophytic mold, Aspergillus fumigatus, in which resistance mutations were acquired after exposure to azole fungicides. 

Strains of micro-organisms resistant to one or more antimicrobial medicines can be transmitted between members of one species. For instance, methicillin-resistant Staphylococcus aureus (MRSA) bacteria can be passed from one human to another, which poses a particular problem to hospitals and nursing homes.

Transmission of resistant strains of bacteria and other microorganisms can also occur between humans and animals. They are passed on via direct contact or via the food chain. This happens in both directions, with potential adverse consequences to the health of both humans and animals. 

For fungal pathogens, patient-to-patient transmission in healthcare settings can recently be attributed to Candida auris. Unlike other Candida species, intra- or interhospital transmission of this emerging pathogen can be related to environmental contamination or personal and device colonisation. 

Misuse and overuse of these drugs upsets the balance between beneficial and unfavourable organisms in microbial communities, and catalyses antimicrobial resistance. This compromises the effectiveness of antimicrobial therapy. In addition, resistant strains may spread to other individuals, and as such jeopardise therapy options for a wider population. Health authorities therefore recommended to avoid unnecessary medication.

The excessive use of antimicrobials in humans and animals has an impact on human health. Antimicrobials that were once proven powerful weapons against infectious diseases lose their effectiveness, and in some cases alternative treatment options (i.e. other types of antimicrobials) are limited. Excessive and improper use of antimicrobials results in the emergence of highly harmful bacteria and fungi, resurgent diseases, and mutating bacteria. This leads to longer hospital stays, higher treatment costs, and sometimes higher mortality. 
Controlling antimicrobial resistance requires cooperation between public health, food, veterinary and environmental authorities, industrial organisations, veterinarians, farmers and several others, who all share responsibility in this area.

Combatting antimicrobial resistance is a high priority for health authorities worldwide. In 2015, the World Health Organisation has put forward its Global action plan on antimicrobial resistance (link is external), which focuses on:

• improving awareness and understanding of antimicrobial resistance
• strengthening knowledge through surveillance and research
• reducing the number of infections (incidence)
• optimising the use of antimicrobials
• developing economic aspects linked to this matter.

Former UK prime minister David Cameron, who made the fight against AMR a political top priority, ordered a study of the world’s as-is from top economist Jim O’Neill. His report (link is external) got world-wide attention, and predicted more deaths from AMR infections than from cancer in 2050.

At European level, the fight against antimicrobial resistance is high on the agenda of the European Medicines Agency (EMA), the European Center for Disease Prevention and Control (ECDC) and the European Food Safety Agency (EFSA). In June 2017, the European Commission adopted the EU One Health action plan against antimicrobial resistance (link is external). It builds on the first 5-year action plan designed to address the growing risks posed by antimicrobial resistance, which was launched in 2011. Both plans embrace a holistic approach in line with the One Health perspective. It involves participation from all sectors and covers all aspects of antimicrobial resistance. 

In Belgium the Federal Public Service for Health, Food Chain Safety and Environment is competent for antibiotics policy and sanitary risks. To do so, they rely on scientific evidence provided by Sciensano and the Superior Health Council.

• Sciensano coordinates national surveillance programmes and surveys of healthcare-associated infections, antimicrobial use and antimicrobial resistance in hospitals and nursing homes. Sciensano furthermore monitors antimicrobial resistance in food pathogens and in animals.
• The Superior Health Council provides independent advice and guidelines on infection control and on the containment of antimicrobial resistance in Belgian healthcare facilities.

Currently, the Federal Public Service of Health, Food Chain Safety and Environment is taking initiative to draft a new One Health national action plan to combat antimicrobial resistance, which will be presented to the next federal ministers. 

The use of antimicrobials in animals must comply with EU and national legislation. Since 1999, the Belgian Antibiotic Policy Coordination Committee (BAPCOC) coordinates different efforts in the framework of a One health approach. The National Antimicrobial Committee (NAC) regularly publishes updated guidelines on which drugs are preferably used to combat specific infections. In the veterinary sector, in July 2016, new Belgian legislation came into force which limits the veterinary use of some antimicrobial classes, critical to treat severe infections in humans, in animals that are part of the food chain, and imposes laboratory diagnosis prior to curative treatment of these animals. Wat geldt er voor mensen? En voor antiviralen, antiparasitairen en antifungals?

Sciensano works in the battle against rising antibiotic resistance in animals in close collaboration with AMCRA (link is external). This organization develops awareness campaigns and strategies, including recommendations and tools for veterinarians and e.g. farmers.

For the management of fungal infections in European settings, guidelines were proposed by the European Society of Clinical Microbiology and Infectious Diseases (ESCMID) Fungal Infection Study Group (link is external). These treatment recommendations were established by a panel of experts, assessing the application of certain antifungal agents. These recommendations depend on the type of patient and the site of infection, and are graded by a score expressing their strength.