Backgrounder:Antimicrobial Applications in the Food System and Resistance Management

Production Agriculture Applications

Antibiotics and fungicides, some of which have identical chemical counterparts in human medicine, have a variety of useful applications in production agriculture. Estimates of use exist, but are influenced by data gaps and inaccuracies. Although the total amount of antibiotics used in human medicine and agriculture is not precisely known, both sectors use appreciable quantities. Estimates of the amount of antibiotics used annually in production agriculture range from 18.4 to 30 million pounds. This compares with estimates for usage in human medicine that range from 4.5 to 32.2 million pounds.

Animal Husbandry. Antibiotics have been used in food animals (primarily cattle, swine, and poultry) for more than 50 years to treat, prevent, or control infectious disease, or to improve efficiency of feed utilization and weight gain. Use of antibiotics in bison production is generally discouraged, occurring only for treatment purposes. In aquaculture, antibiotics are only approved to treat disease and cannot be used prophylactically (for disease prevention) or for growth promotion.

Administration of veterinary drugs to food animals is a critical component of an overall management system to secure the health and welfare of the animals and ensure the safety of the products that enter the food chain. Therapeutic antimicrobial regimens include disease treatment1, control2, and prophylaxis (prevention)3. Antibiotics are administered at low levels to promote growth rate and enhance feed efficiency in healthy livestock. The use of an in-feed antibiotic for growth promotion occurs most often in young, growing animals; use in older animals has a lessened effect. Growth promotion uses allow farmers to produce food animals at less cost because the amount of feed required for an animal to reach production weight is reduced. It is thought that the mechanisms by which growth promotion is achieved are physiological, nutritional, and metabolic in nature, relating to antibiotic inhibition of the normal microflora, which enables more energy to be expended for nutrient use and increased conversion to weight gain.

Plant Agriculture Applications

Fungicides and antibiotics are used in plant agriculture to control fungal and bacterial diseases, e.g., to control fire blight or blister spot in fruit tress. Trees are generally sprayed during blossom time, when they are most susceptible to infection; the edible fruit is not sprayed. A limited number of fruit tree species—apple, pear, and peach—are treated in such a manner.

Food Processing Applications

A variety of “food antimicrobial agents,” including antifungals, sanitizers, and beneficial microorganisms and their inhibitory metabolic products, are applied during food production and manufacturing to improve the efficiency of the system and increase the safety and quality of the product.

Several different types of antimicrobials are used in food manufacturing to either clean, sanitize, or disinfect, by reducing the levels of microorganisms on environmental and food contact surfaces and human skin and preventing cross-contamination. Several types of antimicrobials are also used in food formulations, on food tissues, and on ready-to-eat (RTE) product surfaces to prevent food spoilage and control pathogen growth.

Some food preservatives, such as common table salt, have been in use for hundreds of years, but most others have been extensively applied only in recent decades. Food antimicrobial agents are generally not used alone to control foodborne pathogens, but are included as synergistic components of the “multiple hurdle approach” to microbial control. Common applications of food antimicrobials include use of sodium nitrite to inhibit Clostridium botulinum in cured meats if product temperature abuse occurs, organic acid solutions as spray sanitizers to control pathogens on beef carcasses, nisin and lysozyme to control C. botulinum in pasteurized process cheese, and lactate to control L. monocytogenes in processed RTE meat and poultry products.

Bacteria and/or the antibacterial products of their metabolism may also be used to control undesirable microorganisms. Some bacteria, such as those referred to as lactic acid bacteria (LAB) and which may be naturally-occurring either in the initial microflora of fermented or other foods (e.g., vacuum packaged meats) or added as starter cultures, may be used because they can inhibit the growth of spoilage and pathogenic bacteria by depleting nutrients and oxygen and producing inhibitory metabolic substances such as lactic and acetic acids.

Managing Antimicrobial Resistance

A number of strategies are used throughout the food system, from agricultural production to the home, to manage the risk of antimicrobial resistance. These strategies for minimizing and containing antimicrobial resistance include various antibiotic alternatives and judicious antibiotic use guidelines. Resistance monitoring systems also contribute to risk management.

A variety of guidelines exist for responsible (proper, appropriate, prudent, or judicious) use of antibiotics in human and veterinary medicine. The guidelines recognize that any use of antibiotics, human or animal, has the potential to select for antibiotic resistance and that all uses of antibiotics cannot be eliminated or severely constrained. Therefore, the intent of the documents is to promote appropriate use of antibiotics, maximizing efficacy and minimizing resistance development. In practice, this involves prescribing antibiotic therapy when and only when it is beneficial to the patient, targeting therapy to the desired pathogens, and using the appropriate drug, dose, and treatment duration. Responsible use is not necessarily reduced use, however; antibiotics may offer valuable benefits when used appropriately.

Veterinary and other professionals may use nonantibiotic interventions early in the life of animals to promote healthy animals that do not become ill and are unlikely to need antimicrobial treatment. An example of effective alternatives to antimicrobials is the use of vaccines in the salmon and trout industries to control enteric redmouth disease and vibriosis, where vaccinating young fish “fingerlings” is standard practice. Another example is the use in feed for food animals of one or more types of microorganisms to competitively exclude pathogens, a practice in Europe and other countries. None of such alternative approaches, however, can replace therapeutic antibiotic uses.

The key point of influence that food scientists have in preventing the spread of resistant and sensitive pathogenic microorganisms in foods is preventing them from entering the food supply and, if present, inactivating them or preventing their growth. Food manufacturing interventions that effectively reduce the prevalence of foodborne pathogens also reduce the prevalence of those that are resistant to antibiotics. Use of the multiple hurdle approach likely combats development of resistance to singular antimicrobial food safety interventions.

1 Treatment is the administration of an antimicrobial to an animal or group of animals exhibiting clinical disease.
2 Control is the administration of an antimicrobial to animals, usually as a herd or flock early in the course of disease onset in the population.
3 Prophylaxis is the administration of an antimicrobial to exposed at-risk healthy animals, generally in a herd or flock situation prior to the onset of a disease.