Here are some answers to common questions about antibiotic resistance and livestock.

Q:What is an antibiotic?

A:An antibiotic is a medicine that kills or hinders the growth of microbes such as bacteria and fungi. Today the terms "antibiotic" and "antimicrobial agent" are used to refer to both natural and synthetic compounds used against microbes that can cause disease in humans and animals.

Q:What is antibiotic resistance?

A:Antibiotic resistance is the ability of microbes to adapt to a certain drug. Some bacteria develop the ability to neutralize the antibiotic before it can do harm, while others just pump it out or change in some other way to withstand the antibiotic's attack.

Q:What causes bacteria to become resistant?

A:If one or two microbes survive an antibiotic treatment, they can multiply and replace all the bacteria that were killed off. Also, bacteria can become resistant through mutation of their genetic material or can acquire pieces of DNA that code for resistance from other bacteria.

Q:Why is antibiotic resistance a food safety concern?

A:Resistance is increasing to antibiotics commonly used to treat serious infections from pathogens found in food, such as salmonella and campylobacter. Also, meat from a cow or pig could contain antibiotic-resistant genes, and once ingested by a human, those genes could be transferred to bacteria that cause disease.

Q:Why are antibiotics used in food-producing animals?

A:Antibiotics are used to treat sick animals, to prevent diseases at times when animals are most susceptible and are sometimes given in low doses in feed to promote the growth of cattle, poultry and swine.

Q:How much is used in livestock?

A:The exact amount is unknown because there's no government tracking of such use. The Union of Concerned Scientists asserts that about 25 million pounds a year are used for nontherapeutic purposes alone, while the Animal Health Institute estimates that 20.2 million pounds were produced for farm and companion animals in 2003.

Q:What are the potential consequences for human health?

A:Many scientists believe that increasing antibiotic resistance in bacteria harbored by livestock makes it more likely for infected humans to have a resistant strain. Thus, the illness may last longer, be more serious or more expensive to treat.

Sources: National Center for Zoonotic, Vector-Borne and Enteric Diseases, U.S. Centers for Disease Control and Prevention