A new study led by University of Galway researchers has discovered that swans in the Greater Dublin and County Kildare areas frequently carry antimicrobial resistant (AMR) bacteria in their digestive systems. These bacteria closely resemble those causing difficult-to-treat infections in humans.
The research team, working in collaboration with the Irish Midland Ringing Group, collected fecal samples from 17 swans living across several locations in the Greater Dublin Area. Sampling sites included Broadmeadow Estuary in Swords, Bray harbour, Newbridge in Co Kildare, and along the Grand Canal in Dublin city.
Laboratory analysis revealed that 11 of the 17 samples tested positive for one or more AMR bacteria, with a total of 35 AMR bacteria detected overall. The most prevalent type identified was multidrug-resistant E. coli.
According to the study, the high rate of AMR bacteria detection in swans is likely linked to human-associated pollution of their shared water habitats. This pollution comes from both treated and untreated wastewaters, as well as storm water overflows. However, researchers have not ruled out direct swan-to-swan transmission.
Dr. Liam Burke, lecturer in bacteriology in the School of Medicine at University of Galway and principal investigator for the study, explained that the university had previously conducted research examining AMR bacteria in water.
“We found some of those that are causing infections in humans in canals, in rivers and in coastal areas in a few different places around Ireland, including Dublin, and we always noticed that wherever we found these bacteria, there was always swans present in the canals,” Burke told RTÉ’s Morning Ireland.
“So we decided that it would be worth looking to see whether swans were picking up bacteria that are resistant to these antibiotics.”
Risk of Spread to Humans
Burke highlighted the potential transmission risk to humans, noting that if animals carry drug-resistant bacteria, they can pass them on to people.
“If swans are in parks and other areas where humans might go for recreation, they can spread the bacteria in the water there, and if we are exposed to that water and swallow that water, then there’s potential for us to become colonised with these AMR bacteria,” he explained.
According to The Journal, the consequences could be serious if such bacteria enter the human gut or bloodstream, potentially causing infections that don’t respond to first-line antibiotics, requiring “last resort antibiotics” for treatment.
While considerable research exists on AMR transmission in humans and livestock, Burke noted that the extent to which wild animals can transmit AMR remains “a big knowledge gap” that requires further study.
“It’s important for us to know what are the potential risks of dissemination in wild animals and in the environment,” he said.
The World Health Organisation classifies AMR as one of the top global public health and development threats. A study published in the Lancet estimated that bacterial AMR directly caused 1.27 million global deaths in 2019 and contributed to 4.95 million deaths overall.
Burke emphasized the need to control the spread of AMR bacteria by limiting their dissemination in the environment, particularly through improved wastewater treatment and reduced environmental pollution.
The University of Galway-led study received funding from the EU’s Erasmus+ Programme, the Environmental Protection Agency (EPA), and the Health Service Executive (HSE). Complete findings have been published in the journal Science of the Total Environment.