Healthy living Antibiotic resistance – the role of the environment

Antibiotics are used to treat bacterial infections in humans and animals. They inhibit or kill bacteria and thereby support recovery from bacterial infections. However, not every antibiotic is effective against every type of bacteria. If bacteria are resistant to antibiotics, in other words, insensitive to them, this makes effective treatment of the infection difficult in many cases. Multi-drug resistant bacteria present a particular problem. These bacteria are insensitive to several different classes of antibiotic.

If they are treated with an antibiotic, the resistant bacteria may continue to multiply, while non-resistant bacteria are damaged. In this way, antibiotic-resistant bacteria have a survival advantage over non-resistant bacteria. This can result in an imbalance in the natural bacterial population.

Some types of bacteria are naturally resistant to certain antibiotics. However, there are also many bacteria that, over time, have gradually become insensitive to previously effective antibiotics. This occurs in particular if antibiotics are used unnecessarily or taken without following the instructions provided by the prescribing doctor.

If antibiotics enter the environment, for example, through the sewer system or from agricultural sources, this can also facilitate the emergence of antibiotic-resistant bacteria.

Human and animal sources

Antibiotics are not completely broken down by the metabolic processes in the bodies of humans and animals. This means that they are, in part, excreted in urine and feces – up to 90 percent of some types of antibiotic may be excreted.

Antibiotics, antibiotic residues and antibiotic-resistant bacteria enter the environment primarily through the excretions (urine and feces) of humans and animals. The main routes for this to happen are through the spreading of animal manure, sludge or digestate from biogas plants on fields and the discharge of wastewater from municipal wastewater treatment plants or healthcare facilities such as hospitals. 

Antibiotic residues can enter the sewer system via sewage and, from there, make their way to wastewater treatment plants. Most sewage plants are not currently capable of completely containing micropollutants, including antibiotics. This means that antibiotic residue can enter sewage sludge, which is often spread on fields as a fertilizer. It can also enter the wastewater, some of which ends up in lakes and rivers. 

Antibiotic residue from livestock farming can also enter the environment. If an animal is treated with antibiotics, the residue can end up in fields, meadows and water bodies by being excreted directly in the animal’s feces (on free-range farms) or through the spreading of animal manure and dung on fields. From there, it can also enter the groundwater.

However, antibiotics are found primarily in surface waters and more rarely in groundwater. In drinking water purification plants, steps are taken to ensure that antibiotic residue and bacteria are eliminated from the water. This means that there’s no need to worry about drinking water quality. 

Manufacturing sources

In some countries, such as India, wastewater from manufacturing plants often contains large quantities of antibiotics, which enter the environment this way. Manufacturing plants are therefore one of the main causes of antibiotics entering water and soil in those countries. In Germany, on the other hand, this entry route does not play a significant role. 

Foreign travel

The consumption of antibiotics is much higher in many countries than in Germany. There are more resistant and multi-resistant bacteria in those countries as a result. 

Due to globalization and travel, antibiotic-resistant bacteria from countries with high resistance rates can be imported into Germany. In South and Southeast Asia, for example, resistant and multi-resistant bacteria are widespread, and so there is a high risk of travelers from Germany picking up such bacteria there and carrying them home with them. Around 70 percent of travelers returning from countries such as India and Laos bring back multi-resistant microbes with them.

Antibiotics that enter the environment inhibit environmental bacteria that are sensitive to antibiotics. This gives resistant bacteria a clear survival advantage over non-resistant bacteria and allows them to multiply in greater numbers. Even low concentrations of antibiotics are sufficient to enable the development of resistance.

At the same time, antibiotics in the environment facilitate the development of new resistant bacteria. This happens, for example, when bacteria that are already resistant pass on their resistance genes to other types of bacteria that were previously non-resistant. Wastewater from wastewater treatment plants, sewage sludge and manure are all ideal environments in which this can occur because bacterial populations in this material are particularly dense and they also provide a good source of nourishment for the bacteria. When sewage sludge and manure is spread on fields and wastewater from wastewater treatment plants is discharged into bodies of water, the environmental bacteria that live there can also develop resistance. As a result, there is a risk that ever-increasing numbers of environmental bacteria will become resistant to antibiotics.

In general, the transmission of resistant bacteria from the environment to humans has a more minor role to play. Much more commonly, bacteria are transmitted from human to human, from animal to animal, or between animals and humans – in particular in hospitals and care facilities and in livestock farming.

Nevertheless, the transmission of bacteria (both resistant and non-resistant) from the environment to humans is, in principle, possible in any location where people come into contact with heavily contaminated water or soil. This is the case, for example, if people swim in water bodies with poor water quality or eat unwashed foods (such as salads) that were watered with contaminated water.

In general, though, it is pretty unlikely for someone to ingest enough bacteria in this way to contract an infection. A very large quantity of bacteria is normally required in order for this to happen. Healthy individuals should normally have no reason to worry about swimming in good-quality water.

Moreover, most environmental bacteria don’t transmit diseases. This means that, even if they enter a person’s body and start to reproduce there, they won’t make that person sick. Under certain circumstances, however, these bacteria may pose a problem. If, for example, resistant bacteria from the environment begin to colonize the intestines, they may pass on their antibiotic-resistant genes to the other intestinal bacteria there. Outside of the gut, these intestinal bacteria can cause infections in the body that can be difficult to treat because of antibiotic resistance. These infections can be particularly dangerous for people with a weakened immune system. As a precaution, they can, for example, avoid swimming in natural bodies of water.

One Health

The One Health approach is central to the fight against antibiotic resistance. The health of humans, animals and the environment are all closely intertwined. Seen this way, there is only “one health” to be protected and so a unified approach is necessary across all areas. Pathogens – disease-causing germs – know no boundaries and can spread between people, animals and the environment.

Therefore, measures to prevent antibiotic resistance must be applied in human and veterinary medicine, as well as in agriculture and environmental policy. In addition to helping combat antibiotic resistance, the One Health approach is also important in other areas, such as containing the spread of zoonotic diseases. More than half of all pathogens are zoonotic, which means that they can be transmitted from animals to humans.

Antibiotic resistance strategy

A number of strategies have already been formulated to combat the growth of antibiotic resistance. Foremost among these is the Global Action Plan on Antimicrobial Resistance, which was developed by the World Health Organization (WHO) and other international organizations. In Germany, the German Antibiotic Resistance Strategy (Deutsche Antibiotika-Resistenzstrategie, DART) brings together the key measures. Among other things, it envisages the monitoring and recording of antibiotic consumption and resistance, as well as measures to prevent infection and to ensure correct, appropriate use of antibiotics and increased research activities. In accordance with the One Health approach, these measures apply to both human and veterinary medicine.

Major successes have already been achieved in veterinary medicine. The quantities of antibiotics used in farming have been significantly reduced, with a decline of almost 70 percent recorded between 2011 and 2023. In human medicine too, doctors are now using fewer antibiotics – in outpatient settings, antibiotic use was reduced by about one fifth between 2010 and 2018. After a further reduction during the COVID pandemic in 2020 and 2021, antibiotic resistance has begun to increase again in recent years. However, antibiotic use in 2023 was at a similar level to before the pandemic. If fewer antibiotics are used, fewer will be able to enter the environment.

Improvements in wastewater plant technology

Efforts are also being made to improve wastewater treatment technology so that antibiotic residues can be filtered out. Effective methods have already been identified. For example, many active ingredients in antibiotics can be removed using ozone and activated carbon.

Everyone has a part to play

To avoid becoming infected with bacteria from the environment, be sure to only swim in natural bodies of water known to have a good water quality. Good food hygiene can also help prevent infection. For example, be sure to wash fruit and vegetables thoroughly before eating them.

To find out how everyone can play their part in reducing the number of new antibiotic-resistant pathogens that can develop, read the article discussing antibiotic resistance.