Questions and Answers: Animal Antibiotics, Antimicrobial Resistance and Impact on Food Safety

Animal antibiotics Q&A_0.jpg

For more than 50 years, veterinarians and producers have administered antibiotics to food animals, primarily poultry, swine, and cattle, mostly to fight or prevent animal diseases. The following Q&A provides answers to common questions about antibiotic use in animals, including information on why antibiotics are used in food animals and how animal antibiotics are regulated. Furthermore, overall concerns about the overuse of animal antibiotics in food animals are addressed, as well as mechanisms that are currently in place to minimize the overall risk to human health. Antibiotic residues in animal food products, such as meat, milk, and eggs are also discussed and several credible resources are listed to provide information on animal antibiotics and antimicrobial resistance as they relate to food safety.

How do we use the terms “antibiotics” and “antimicrobials” in this Q/A?
Antibiotics refer to drugs thatare used to treat infectious diseases in humans, animals or plants. They work by inhibiting the growth of or killing microorganisms causing the disease. Antimicrobials is a broader term that refers to any compound, including antibiotics, sanitizers, disinfectants, a number of food preservatives and other substances, that acts to inhibit the growth of or kill microorganisms.

Why are antibiotics used in food animals?
Antibiotics are used in animals for the same reason as for people: to treat and control diseases. Protecting the health of animals helps to protect human health. About 60% of diseases that impact humans come from animals, so the link between animal health and human health is strong. Maintaining health among both populations is critical, according leading health organizations worldwide, including the World Health Organization and the U.S. Centers for Disease Control.

FDA also has approved the use of some antimicrobials for the promotion of growth in certain livestock and also poultry. However, no matter whether antimicrobials are used to treat disease or to promote growth, FDA safeguards are in place to ensure safe food.

How are antibiotics for animals regulated by the government?
In addition to regulating certain foods, the FDA has responsibility for regulating drugs, including antibiotics that are administered to animals that produce food. For each proposed drug, extensive scientific studies that evaluate the efficacy and safety in animals, in addition to the safety for humans who consume foodstuffs derived from treated animals, must be submitted to FDA by a pharmaceutical sponsor. The FDA evaluates these and all relevant studies and then makes a determination as to whether the medicine is effective in preventing and/or treating disease, as well as whether it poses a risk to consumers of animal products. The FDA also imposes any necessary rules on how the medicine must be used to ensure safety for both people and animals.

For each approved pharmaceutical, the FDA reviews and approves the route(s) of administration (in water, in feed or by injection), the particular species for which it can be used and the specific diseases that the antibiotic should be used to treat. Approved antibiotics may, in some instances, be used in different species and diseases, which is referred to as “off-label” or “extra-label” use. The FDA has specific guidelines on the circumstances under which extra-label use of drugs may occur, but in some instances, FDA prohibits this use to protect human or animal health or both.

FDA’s Center for Veterinary Medicine (CVM) published a final guidance document in April 2012 to eliminate the use of antimicrobial drugs for growth promotion purposes.

The guidance proposes two principles aimed at proper and judicious use of antibiotics in food-producing animals. The first is that these medicines should only be used when they are needed to assure animal health. FDA does not consider the use of these medicines to promote growth as necessary for animal health, and believes this type of use should end. The second principle is that these medicines should only be used with veterinary oversight or consultation. According to FDA, veterinarians have the scientific and clinical training necessary to ensure that medically important antibiotics are used on the farm in a judicious and appropriate manner.

FDA and food and animal health stakeholders and pharmaceutical companies are working cooperatively to phase out growth promotion uses of antibiotics. FDA is in the process of defining a process by which these medicines could only be used in feed products for treatment, control and/or prevention of disease. As a result, these medically important antibiotics would require veterinary oversight. This means that a veterinarian would be involved in the decision to add antibiotics to animal feed.

What is antibiotic or antimicrobial resistance?
Antibiotic resistance refers to the ability of certain bacteria to “resist” and survive after they have been exposed to a specific antibiotic or antimicrobial that normally would be expected to kill them or inhibit their growth. Antibiotic resistance may occur through various mechanisms. For example, bacteria may become resistant by developing a genetic mutation that provides a survival advantage or may acquire a survival trait through genetic material from neighboring bacteria. The bottom line is that plants, animals and bacteria can evolve over time to adapt to environmental changes. Antibiotic resistance is one example of that phenomenon.

What are the implications and specific human health concerns related to antibiotic resistance among foodborne pathogens?
The primary concern relates to the potential that the use of antimicrobial drugs in animals could contribute to increases in antibiotic resistance among bacteria that cause foodborne illnesses in people. Although the occurrence of foodborne illnesses has in general declined in the U.S. over the past decade, people still get sick from pathogens in food, and some of those pathogens may be resistant to particular antibiotics. For most healthy people, the vast majority of foodborne illnesses, including those caused by resistant bacteria, are not severe enough to require antibiotic treatment. For some people, most notably children, the elderly, and those with compromised immune systems, however, antibiotics may be necessary to resolve the illness. If a foodborne disease requires treatment with an antibiotic and the bacteria are resistant to it, then the severity of the disease could increase with consequences such as lengthening of the disease, increased rates of hospitalization or, in extreme cases, increased risk of death.

Does the use of antibiotics in food animals lead to resistant bacteria in meat that can make people sick? When food animals are given antibiotics, resistant bacteria could emerge and multiply in the intestinal tract of the animal the same way that can happen in people when antibiotics are used to treat infections. Some of these bacteria in the food animal might contaminate the surface of its meat during processing. If the meat is not thoroughly cooked to kill these bacteria, and enough organisms are present to infect a person, they could cause a foodborne illness. If antimicrobial therapy is needed, and the causative organisms are resistant, the drug may not be as effective in helping to cure the infection and prolonged illness could result.

Even though it is difficult for scientists to identify when this chain of events actually occurs, the FDA nevertheless assesses this human food safety risk and it either denies approval or restricts an antibiotic’s use based on the level of risk identified.

Moreover, in 2006 an expert panel convened by the Institute of Food Technologists (IFT) concluded that the extent to which antibiotic use in food animals leads to antibiotic-resistant infections in humans is unknown due to the lack of conclusive scientific research, and it recommended that much more research be conducted. The complexity of the question overall is described by the following points made in the Expert Panel’s report, “Antimicrobial Resistance: Implications for the Food System

The science indicates that antibiotic use in food animals is only one of many pressures that could cause resistant bacteria to emerge and spread. To the point, antibiotic-resistant bacteria are found in meat from livestock raised both with and without exposure to antibiotics.

  • Trends in the prevalence of resistance in bacteria do not necessarily reflect trends in the incidences of either foodborne illness or resistant infections, which in many cases have declined in recent years.
  • It is difficult to correlate antibiotic resistance among foodborne pathogens with antibiotic uses on the farm, and an increased incidence of illness in any given year may or may not parallel increased use of antibiotics potentially selecting for resistant bacteria.

Overall, the Panel stated that no one strategy, even eliminating antibiotic use on farms, removes the risk of resistant bacteria in food. Instead, it made a number of specific recommendations that included strengthening risk assessments to guide FDA’s approvals of antibiotics, responsible use of antibiotics on the farm, continued emphasis of Hazard Analysis and Critical Control Points (HACCP) interventions throughout the food chain and focused research for better understanding of resistance among bacteria.

HACCP is a systematic preventive approach to food safety that addresses physical, chemical and biological hazards as a means of prevention rather than finished product inspection. HACCP is used to identify potential food safety hazards, so that key actions can be taken at key points, known as Critical Control Points (CCP’s), where the hazards can be reduced or eliminated. The system is used at all stages of food production and preparation processes.

What is the greatest risk factor for people acquiring a resistant foodborne pathogen?
According to IFT’s expert panel of scientists, scientific studies show that one of the greatest risk factors associated with acquiring a resistant foodborne pathogen is the individual’s prior use of antibiotics. Physicians should prescribe antibiotics appropriately and consumers should use antibiotics according to the prescription. Antibiotics should not be used when they are not warranted—e.g., for treating viral infections such as the common cold or a stomach virus. When antibiotics are the appropriate course of treatment for bacterial illness, it is extremely important that the correct one be used and that patients are compliant in taking their medication as prescribed.

Even though studies can’t quantify the extent to which antibiotic use in animals is causing resistant infections in people, what is being done to minimize the risk overall?
Milk, meat and poultry products are among the most rigorously regulated consumer foods in the U.S. Several layers of protection have been put into place to ensure that antimicrobial drugs used to keep animals healthy are doing so without creating a threat to public health. FDA and the U.S. Department of Agriculture (USDA), along with animal health groups, have introduced several human health protection programs and activities during the past decade including:

  • FDA Regulation: In 2003, FDA finalized an additional safety measure in its regulatory process that “for the first time outlines a comprehensive, evidence-based approach to preventing antimicrobial resistance that may result from the use of antimicrobial drugs in animals” (FDA NEWS, October 23, 2003). This new regulatory evaluation, commonly referred to as “Guidance 152,” establishes a rigorous, three-pronged qualitative risk assessment to estimate a product’s safety with respect to antibiotic resistance. If the assessment shows that the use of the particular antibiotic would lead to adverse human health consequences, FDA may either deny the application for marketing authorization or approve the application, but under specific conditions designed to ensure the antimicrobial drug would not pose a human health risk. See: “Evaluating the safety antimicrobial new animal drugs with regard to their microbiological effects on bacteria of human health concern” for more information.
  • Judicious use: Responsible antibiotic use programs specific to each animal species are in place to guide the judicious use of antibiotics within the health management programs established by veterinarians and producers. For more information go to:
  • Monitoring: Government agencies monitor antimicrobial-resistant bacteria at various points in the food chain, including at slaughter and retail, which can aid in identifying the emergence of antimicrobial-resistant bacteria and track trends in the occurrence of that resistance. For more information, go to:
  • Bacterial reduction/elimination strategies: IFT’s expert panel of scientists noted that current HACCP systems aimed at eliminating overall bacterial loads in food commodities are likely the most important strategies for reducing risk of foodborne infections in people, including those that are due to resistant bacteria.

Can resistant bacteria and foodborne illness be eliminated or reduced?
IFT’s expert panel of scientists concluded that targeting specific antibiotic-resistant foodborne pathogens may not be the path to reducing this type of illness. Rather, a HACCP approach throughout the food chain could be the most effective way to control pathogens and reduce foodborne infections, including those that could be due to resistant bacteria. This method–applying interventions more generally to control foodborne pathogens rather than focusing on antibiotic resistant strains — would likely have the greater impact on reducing foodborne illness overall.

What is methicillin-resistant Staphylococcus aureus (MRSA) and can people get MRSA from eating meat?MRSA is a type of bacterium that is resistant to methicillin and other commonly-used antibiotics. Life-threatening infections occur among patients in hospitals and healthcare settings who have weakened immune systems. Less threatening infections can occur among healthy individuals within communities. While experts believe more research is needed to assess the potential of MRSA in foods, the CDC states there are currently no data to suggest that MRSA can be transmitted from meat consumption or even meat handling.

What effect does cooking have on foodborne bacteria?
Thoroughly cooking meat, poultry, and eggs, and following the basic safe food handling and kitchen sanitation practices will greatly reduce the risk of foodborne disease–including foodborne disease that could be caused by resistant bacteria. Frequent hand-washing is one of the most important disease-prevention techniques, as is cleaning food preparation surfaces and utensils with soap and warm water before and after use.

For more information about safe food handling see FightBAC! and “A Consumer’s Guide to Food Safety.”

Antibiotic residues
Is there a threat to food safety from antibiotic residues in food products?
Although concerns have been raised in the past about antibiotic residues in food, governmental regulatory controls and their compliance by veterinarians and producers have made occurrences of volatile residues extremely rare. Livestock handlers must adhere to FDA regulations when administering antibiotics to an animal. Regulations include a specified withdrawal time for each antibiotic used to ensure that the animal’s system has been sufficiently cleared of antibiotics before its meat or milk enters the food supply. In establishing withdrawal times, FDA applies wide margins of safety to ensure safe food. FDA, USDA and food processors routinely sample milk and meat to verify that producers are adhering to withdrawal requirements.

Who specifically regulates residues in milk and meat?
Primarily the FDA and the Food Safety and Inspection Service (FSIS) of USDA are involved in the regulation and control of antibiotic residues in meat, poultry and egg products. FSIS’ National Residue Program, in place since 1967, has used a variety of strategies to prevent antibiotic residues that exceed an established tolerance (violative) from entering the food supply. It includes testing for approved and unapproved drugs known or suspected to be used in food animals. FSIS samples meat for residues and reports any violations to FDA.

Milk is extensively monitored through state regulatory agencies, which act under contracts with FDA. Mandatory reporting is required by state agencies under the National Conference on Interstate Milk Shipments. The Grade “A” Milk Pasteurized Milk Ordinance is the set of rules by which state regulatory agencies implement their Grade “A” milk programs. Residue samples are taken at multiple points between farm and consumer to ensure compliance, and if a tank of milk is found to have violative residues, it is rejected for human consumption.


CDC: Preliminary FoodNet Data on the Incidence of Infection with Pathogens Transmitted Commonly Through Food – 10 Sites, United States, 2004.

Doyle et al., Institute of Food Technologists, “Antimicrobial Resistance: Implications for the Food System” Comprehensive Reviews in Food Science and Food Safety, Vol.5, Issue 3, 2006.

National Milk Drug Residue Data Base, Fiscal Year 2005 Annual Report, October 2, 2004 – September 30, 2005. GHH, Inc., Contract No. 223-05-4200, February 15, 2006.


Related Links

Guidance for Industry: Evaluating the Safety of Antimicrobial New Animal Drugs with Regard to Their Microbiological Effects on Bacteria of Human Health Concern

Healthcare-Associated Methicillin Resistant Staphylococcus aureus (HA-MRSA) – CDC

2004 FSIS National Residue Program

2003 FSIS National Residue Program Data

“Consumer’s Guide to Food Safety Risks”

Partnership for Food Safety Education