SYDNEY, June 9 (Xinhua) -- Antibiotic residues and their breakdown products in wastewater are contributing to the global rise of antimicrobial resistance, new research has revealed.

A joint study by Australia's University of Queensland (UQ) and the University of Exeter in Britain found that "transformation products" -- chemical compounds formed as antibiotics degrade -- can drive bacterial resistance at levels comparable to the original drugs, a UQ statement said Tuesday.

Researchers said up to 90 percent of antibiotics consumed by humans are excreted and enter sewage systems, ultimately reaching wastewater treatment plants, which can act as "hidden reservoirs of bioactivity," with both antibiotics and their by-products contributing to resistance.

"Wastewater treatment is widely considered to reduce antibiotic concentrations and biological activity, although not necessarily eliminate them," said UQ PhD candidate Pooja Lakhey, lead author of the study published in Nature Water.

Wastewater samples collected in Queensland, Australia, and Cornwall, England, showed bacteria developed resistance when exposed to antibiotic breakdown products from three antibiotic classes.

Antimicrobial resistance, often called a "silent pandemic," is linked to about 5 million deaths annually and can lead to an inability to treat infections, the study shows.

"The real issues are that humans use too many antibiotics and their breakdown products continue to drive antibiotic resistance," said Jake O'Brien from UQ's Queensland Alliance for Environmental Health Sciences.

The researchers called for a risk assessment that accounts for both antibiotics and their degradation products, which are currently not routinely monitored.