LOS ANGELES (Reuters) - Maryland has become the second U.S. state to pass a law banning the routine use of antibiotics in healthy livestock and poultry, a move aimed at battling the rise of dangerous antibiotic-resistant bacteria known as “superbugs.”

Maryland’s Keep Antibiotics Effective Act, which aims to end a practice that public health experts say can fuel the spread of superbugs, takes effect on Oct. 1 after Governor Larry Hogan declined to sign or veto it last week. Farmers in Maryland have until Jan. 1, 2018, to comply with the law.

Roughly 70 percent of antibiotics important for human medicine are sold in the United States for use in meat and dairy production. Medical researchers say overuse of such drugs diminishes their effectiveness in fighting disease in humans by contributing to antibiotic resistance.

The World Health Organization has warned that human infections from antibiotic-resistant bacteria pose a grave threat to global health. Such infections are estimated to kill at least 23,000 Americans annually, although a recent Reuters investigation found that many infection-related deaths are uncounted.

California in 2015 adopted tough rules for antibiotic use on farms. Its law, which takes effect on Jan. 1, also restricts the regular use of antibiotics for disease prevention and bans antibiotic use to fatten up animals.

The laws in Maryland and California go further than the U.S. Food and Drug Administration’s guidelines, which seek to prohibit the use of antibiotics for growth promotion in farm animals but do not address the routine use of antibiotics for disease prevention.

The new state rules reserve antibiotic use solely for the treatment of sick animals or to control a verified disease outbreak, not for routine disease prevention, said Matthew Wellington, antibiotics program director for U.S. PIRG, which supported the Maryland legislation. Opponents included the Maryland Farm Bureau.

The laws come as restaurant chains such as Chipotle Mexican Grill Inc, Panera Bread Co, McDonald’s Corp and Subway are working with their meat suppliers to curb the use of important human antibiotics.

Maryland-based Perdue Farms, a major U.S. poultry supplier and the state’s largest, is already compliant. The company says that as of February 2016, more than two-thirds of its chickens and half of its turkeys are raised with no antibiotics.