Antibiotics excreted by patients promote antibiotic-resistant bacteria in hospital sewers, according to a new study of 10 Swedish hospitals.
“To my best knowledge, this is the first direct field evidence in over 25 years conclusively linking observed environmental effects to pharmaceuticals excreted from humans,” says study author Joakim Larsson, professor of environmental pharmacology at the University of Gothenburg.
The study, published in Nature Communications, examined sewer systems and wastewater from hospitals and municipal treatment plants in eight Swedish cities. Sewage from all ten hospitals promoted antibiotic-resistant bacteria, while no such effects were found after exposure to sewage from the corresponding municipal treatment plants.
When the team made a sensitive E. coli strain resistant to fluoroquinolones and penicillin-like antibiotics, it was able to grow well in hospital sewage where it otherwise could not. This showed that it was primarily these antibiotic classes that were responsible for giving resistant bacteria an advantage.
Ciprofloxacin was identified as a key driver, a commonly used antibiotic in the fluoroquinolone group often prescribed for urinary tract infections. Cefotaxime, a penicillin-like antibiotic only used at hospitals, also contributed. Several independent lines of evidence, including chemical analyses and studies of bacterial cell responses, pointed in the same direction.
The research team is currently working intensively to develop a simple, targeted treatment method to reduce the selection pressure in the sewers.
Most conclusions about environmental effects of pharmaceuticals are based on experiments where researchers intentionally add drugs at concentrations matching those measured in the environment. Such studies show what effects drugs can cause, but not whether those effects actually occur under real-world environmental conditions. The current study goes one step further by documenting effects directly within hospital sewer pipes.
Data from University of Gothenburg