Antibiotics in the environment

Before we started using antibiotics as medicines, antibiotic resistance in human and animal pathogens was not common. Today, multidrug-resistant bacteria are a major threat to our health. So then, from where do these resistant and multidrug-resistant bacteria emerge?

Selection of resistance in bacteria in the body during antibiotic treatment is one important source, especially in health care facilities where antibiotic use is high. More and more scientific evidence also suggests that antibiotic resistance genes and antibiotics in the environment play an important role both in the emergence and spread of resistance (reviewed in). All resistance genes in the environment can be regarded as a big “pool” of resistance genes (a “resistome”) that can potentially transfer to pathogenic bacteria.

Sources of environmental pollution

Waste from large-scale animal farms, use in aquaculture and wastewater from antibiotic manufacturing, hospitals and municipalities are major sources of antibiotic resistance genes and antibiotic pollution in the environment. Parts of the antibiotics given to humans and animals are excreted unaltered in feces and urine. In the case of waste from animals, manure is rich in nutrients and is often used as fertilizer on crop fields, leading to direct contamination of the environment with both antibiotic residues and resistant bacteria.

Two potential threats to human health

There are two potential distinct threats where environmental contamination with antibiotics and antibiotic resistance elements can have severe consequences for human health (not considering potential direct toxic effects):

1. Spread of resistant bacteria or resistance genes
2. Emergence of new resistance in pathogenic bacteria

There have been reports on antibiotics and antibiotic resistant bacteria found in river water and sediments. As just one example, urban river water samples in Baltimore contained more pharmaceutics, including antibiotics, than suburban samples. The presence of antibiotics in the water also affected the microbial communities in the rivers..

Will resistance spread to pathogenic bacteria?

The probability that resistance genes in environmental bacteria are transferred to and maintained by pathogenic bacteria may be low. However, if this happens, it will have major consequences. Also, as the types and abundance of antibiotic resistance genes in the environment increases, and the time they stay there, so does the risk that it will happen. Wastewater treatment plants may contribute in this process, as it is a place where bacteria from the environment meet human pathogenic bacteria as well as bacteria that are part of our normal human flora without causing disease. Multidrug-resistant bacteria have been detected in high numbers in treatment plants.

Another study has provided evidence that certain resistance genes from soil bacteria share similarities with resistance genes in bacteria that are infecting humans. This indicates that soil bacteria can be a direct source of resistance for pathogenic bacteria.

Resistant bacteria and antibiotics in the environment have severe consequences

The accumulation of antibiotic resistant bacteria and antibiotics in the environment can have severe consequences. Humans may become directly sick or colonized by antibiotic resistant bacteria when consuming contaminated food or water or through direct contact with animals. In addition, antibiotics also provide a selection pressure for environmental bacteria to maintain antibiotic resistance mechanisms. They may also increase the risk that novel resistant pathogenic bacteria arise and spread. It is crucial to understand that it is all use of antibiotics, whether appropriate or not, that is the cause of increased prevalence and rapid spread of antibiotic resistance as well as the emergence of new, multidrug-resistant pathogens that are threatening our entire health system.

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