WASHINGTON (AFP) - Fast-food giant McDonald's announced Wednesday it would stop serving chicken raised with antibiotics that are important to human health, as worries grow over resistance to crucial drugs.

McDonald's, primarily a hamburger chain but which also sells a number of chicken-based meals, said it has been working closely with poultry farmers to cut back the use of antibiotics.

The move will help prod changes by the large industrial chicken suppliers which have fostered widespread use of human antibiotics among growers.

McDonald's said that it hoped to implement the new restrictions at its 14,000 US restaurants over the next two years.

"While McDonald's will only source chicken raised without antibiotics important to human medicine, the farmers who supply chicken for its menu will continue to responsibly use ionophores, a type of antibiotic not used for humans that helps keep chickens healthy," the company said.

Earlier this week, the company released a new policy statement saying it would follow the World Health Organisation's guidelines on not using antimicrobials in livestock , including important antibiotics, that are considered critically important in human medicine.

The antimicrobials it accepts from poultry suppliers, it said, will be limited to use for treatment and prevention of animal disease, and not for growth enhancement.