10 October 2023

Gulls can sometimes be a nuisance for people who want to enjoy a picnic or an ice cream. They can also be carriers of genes that make bacteria resistant to antibiotics. This is shown by the research led by Jonas Bonnedahl, researcher at Linköping University.

A scientist puts a GPS transmitter on a white star.
Jonas Bonnedahl with a glaucous gull with a transmitter on its back. The photo was taken at the landfill in the town of Bethel, Alaska, USA.

In the latest issue of the prestigious scientific journal Science, the research on antibiotic resistance that is ongoing at Linköping University is highlighted.

Bonnedahl and his colleagues have studied gulls around the world and taken samples of their feces to find bacteria that have antimicrobial resistance (AMR). AMR means that bacteria can survive despite treatment with antibiotics, which can lead to serious infections in humans and animals.

"We often find AMR genes in gulls that are identical to those found in humans. This suggests that there is an exchange of genes between us", says Bonnedahl.

Traces the movements and feces of the gulls

The researchers’ hypothesis is that the gulls ingest the resistant bacteria by feeding from sewage treatment plants and landfills, where it is well known that resistant bacteria accumulate. Then there is a risk that the birds spread the bacteria further through their droppings, which can end up on food or water that people consume. Four people working with a gull.Mariëlle van Toor, Jonas Bonnedahl, and Jonas Waldenström (left to right) teach an aide to tag a gull. Photo credit J. COHEN/SCIENCE

"By attaching transmitters with GPS positioning, we can study the movements and migration of the gulls in detail. In this way, we hope to be able to identify risk environments where the birds can pick up resistant bacteria, but also to which environments they risk spreading these resistant bacteria further".

In an ongoing study, they have discovered that herring gulls feed from sewage treatment plants in addition to visiting fields with crops, pastures and beaches, for example.

Much of the analyzes remain, but already now the research group can state that herring gull can be a vector for spreading antibiotic resistance between humans and the environment. The ongoing research has also shown how the annual migration of different gull birds takes place over long distances sometimes over continents which increases the risk of spreading AMR genes to new places.

Climate change can worsen the problem

The researchers also warn that climate change can make the situation worse. Extreme weather events such as increased precipitation and drought can contribute to spreading AMR genes. In case of large amounts of precipitation, sewage treatment plants are often forced to so-called “widening” ie that part of the wastewater is released untreated. In drought, birds and other animals can also gather at fewer water sources and share microbes.

"We need to identify where AMR comes from and how it spreads in the environment, so that we can find strategies to reduce the effects", says Bonnedahl.

AMR is a global threat to public health, causing millions of deaths each year. According to a report in The Lancet, an estimated 1.27 million people died in the world in 2018 due to untreatable infections caused by AMR.

The gulls are not guilty

Bonnedahl emphasizes, however, that the gulls are not the real villains in the drama. It is how we humans use and release antibiotics and other environmental toxins that are behind the problem.

"We should not blame the gulls. We should blame ourselves for releasing AMR in a way that makes them ingest it", he says.

He suggests that one could improve the purification of wastewater, ensure that birds do not have access to purification basins and have covered landfills.

"We must act quickly and coordinatedly to limit the spread of AMR, otherwise we risk losing the effect of antibiotics that we take for granted today", he says.


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