How does antibiotic resistance spread?

Resistant bacteria are transmitted between humans and animals in exactly the same way as non-resistant bacteria, through many different and complex transmission modes.

Every time antibiotics are used, this encourages the emergence of resistant bacteria. Using antibiotics to treat non-bacterial infections, or failure to follow the doctor’s instructions, accelerates the spread of such bacteria. Doctors and vets are responsible for prescribing antibiotics sensibly, but it is the responsibility of patients and animal owners to make sure that the drugs are taken according to the instructions. However, the best way of avoiding antibiotic resistance and not contributing to its dissemination is to avoid infection in the first place, and to avoid infecting others.

Where can resistant bacteria be found?

Bacteria are to be found everywhere on the planet: on and in living beings, but also in the air, in water and in the soil. Without them, life on Earth would be impossible. Antibiotic-resistant bacteria (whether pathogenic or not) are also present just about everywhere, because bacteria and fungi have been making them to defend themselves for billions of years. Nevertheless, various forms of resistance did develop further only when humans began using antibiotics, for themselves and for their pets and farm animals.  

Like any other medicines consumed by humans, antibiotics and resistant bacteria are excreted and evacuated through the sewers and end up in the waste water treatment plants, of which there are around 700 in Switzerland. The treatment of the water removes most of the antibiotics and bacteria but not all of them, which is why it is also possible to find antibiotic-resistant bacteria in the ‘cleansed’ water exiting the water treatment plants. The water treatment plants in Switzerland are being upgraded to become better able to eliminate different sorts of micro-pollutants, including antibiotics; in the medium term, this should reduce the presence of antibiotics and resistant bacteria in water.  

Antibiotics are also used in animal husbandry and agriculture. Farm animals and food products (including vegetables) can therefore also contain resistant bacteria. In raw meat, it is unfortunately not rare to find the very same strains as those that are detected in hospitalised patients.  

Antibiotic resistance thus needs to be understood according to the One Health concept, i.e. by taking into account all the factors that can influence it:

  • Human health
  • The health of people’s pets
  • The health of farm animals
  • Environmental factors.

How are resistant bacteria transmitted?

Resistant bacteria are transmitted between humans and animals in exactly the same way as non-resistant bacteria. Since they use many different and complex transmission modes, they not only move from one individual to another, but also from one species to another. The most common mod of bacterial transmission appears to be by touching hands, in direct contact with a person carrying bacteria (who may or may not be ill), or by touching contaminated surfaces.  

Resistant bacteria appearing after a course of antibiotics can easily be transferred from a person to a family pet, or vice-versa. Resistant antibiotics can also be transmitted to humans by farm animals: for example, a farmer can catch resistant bacteria from an animal being treated for an infection. These bacteria can also infect raw meat during the slaughtering process.  

Since they are not entirely eliminated by the waste water treatment plants, resistant bacteria can end up in surface waters (rivers and lakes) and in underground aquifers. Watering, irrigation and manuring can deposit them on fruit and vegetables.  

The propagation of resistant bacteria is accelerated by travelling and international trade, and by their ability to exchange genetic material with each other.

Last modification 14.05.2019

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