SYDNEY - Australian birds that live close to urban populations have been found to carry a drug-resistant superbug in far higher numbers than previously thought, a new study revealed Tuesday.

Bird populations including seagulls, penguins and pigeons have all been found to carry Escherichia coli (E. coli), a strain of drug resistant bacteria which is potentially harmful to humans.

Scientists from Australia's Murdoch University found that half of the seagulls tested carried the strain, a figure which was previously believed to be just two in ten.

The bacteria can cause serious infections in people such as urinary tract infections and sepsis, and its presence in wildlife will further reduce the time critical for antibiotics to remain effective, according to the researchers.

Researchers believe that the birds are contracting the bacteria through contact with human waste, and warned that it can be transferred back to humans, or to livestock or domestic animals through environmental contamination.

"We don't know specifically how the birds are picking up the bacteria but suspect it could be from the landfill sites where the gulls routinely forage, and in particular, from nappies, incontinence pads and other waste at these sites," the university's antimicrobial researcher Sam Abraham said.

"The gulls then spread the pathogen to other bird species, which is how we suspect penguins and pigeons are also carriers given they have different lifestyles and do not forage in waste as seagulls do," he said.

Animals located on the popular metropolitan tourist site, Penguin Island in Western Australia, were found to be infected with the bacteria in concerning numbers.

"The bacteria were found in one in every two seagulls but were also detected in one in every ten penguins and feral pigeons," Abraham said.

"This suggests scavenging birds such as seagulls are likely to pick the bacteria up from humans and are then transferring it to other bird species at breeding colonies or watering points," he added.