Antimicrobial Resistance: Implications for the Food System Microorganisms have an inherent ability to evolve—to mutate and adapt to environmental stressors─allowing them to survive otherwise lethal conditions.

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Antimicrobial Applications

During food production and manufacturing, a variety of antimicrobials, including antibiotics, antifungals, sanitizers, and food preservatives, are applied to improve the efficiency of the system, and increase the safety and quality of the product. The multiple points throughout the ecosystem where antimicrobials may be used and subsequently impact the epidemiology of resistance are shown in Figures 1 and 2. Microorganisms encounter and are subjected to a variety of antimicrobial stressors as they move throughout the food system, from the environment to the plant, through food processing, shipping, distribution, storage, and into kitchen food preparation areas. The variety of antimicrobial uses at each of the various stages of the food system may create selective pressure that promotes resistance.

Epidemiology of antimicrobial resistance (adapted and modified from Linton [1977] by Rebecca Irwin, Health Canada [Prescott 2000] and IFT, with permission).
Figure 1–Epidemiology of antimicrobial resistance (adapted and modified from Linton [1977] by Rebecca Irwin, Health Canada [Prescott 2000] and IFT, with permission).
Application of antimicrobials from farm to table
Figure 2–Application of antimicrobials from farm to table

The major classes of antibiotics and their various uses in animals, plants, and humans are listed in Table 2. Detailed information on the mechanism of action of specific classes of antimicrobials can be found elsewhere (Prescott and others 2000; Walsh and others 2003). Some of the antibiotics and fungicides used in agriculture have identical chemical counterparts in human medicine. The majority of antibiotics used in food animals belong to classes of antibiotics that are also used to treat human illness; these include tetracyclines, sulfonamides, penicillins, macrolides, fluoroquinolones, cephalosporins, aminoglycosides (gentamicin and kanamycin), chloramphenicols, and streptogramins (NARMS 2006).

Table 2–Examples of antimicrobial drugs and antibiotics, by major class, approved in the United States for animal, plant, or human use


Antimicrobial, drug class (selected examples) Mode of action/spectrum Food animal use Plant use Human use

Animal Species Disease treatment Disease prevention Growth promotion
Aminoglycosides (gentamycin, neomycin, streptomycin) Inhibit protein synthesis/broad spectrum Beef cattle, goats, poultry, sheep, swine
• (Certain plants)
Beta-lactams penicillins (amoxicillin, ampicillin) Inhibit cell wall synthesis Beef cattle, dairy cows, fowl, poultry sheep, swine
cephalosporins 1st generation (cefadroxil) Broad spectrum
cephalosporins 2nd generation (cefuroxime)

cephalosporins 3rd generation (ceftiofur) Beef cattle, dairy cows, poultry, sheep swine

Chloramphenicol Inhibit protein synthesis/
(Florfenicol) broad spectrum

Inhibit protein synthesis/broad spectrum Beef cattle
Cycloserines (cycloserine) Inhibit cell wall synthesis/narrow spectrum
Glycopeptides (vancomycin) Inhibit cell wall synthesis/narrow spectrum
Ionophores (monensin, salinomycin, semduramicin, lasalocid) Disrupts osmotic balance/narrow spectrum Beef cattle, fowl, goats, poultry, rabbits, sheep
Lincosamides (lincomycin) Inhibit protein synthesis/narrow spectrum Poultry, swine
Macrolides (tylosin, tilmicosin erythromycin) Inhibit protein synthesis/narrow spectrum Beef cattle, poultry, swine
Monobactrams (aztreonam) Inhibit cell wall synthesis broad spectrum
Polypeptides Inhibit cell Fowl, poultry,
(bacitracin) wall synthesis narrow spectrum swine

Fluoroquinolones Inhibit DNA Beef cattle
(enrofloxacin, danofloxacin) synthesis/broad spectrum
Streptogramins (virginiamycin) Inhibit protein synthesis/narrow spectrum Beef cattle, poultry, swine
Sulfonamides (sulfadimethoxine sulfamethazine sulfisoxazole) Inhibit folic acid synthesis/broad spectrum Beef cattle, dairy cows, fowl, poultry, swine, catfish, trout, salmon

Tetracyclines (chlortetracycline oxytetracycline tetracycline) Inhibit protein synthesis/broad spectrum Beef cattle, dairy cows, fowl, honey bees, poultry sheep, swine, catfish, trout, salmon, lobster • (Certain plants)
Others
Bambermycin Inhibit cell wall synthesis/narrow spectrum Beef cattle, poultry, swine

Carbadox Inhibits DNA swine synthesis/narrow spectrum

Novobiocin Inhibits DNA gyrase/narrow spectrum Fowl, poultry
Spectinomycin inhibit protein synthesis/narrow Poultry, swine


aPoultry includes at least one of the following birds: broiler chickens, laying hens, and turkeys.
bFowl includes at least one of the following birds: ducks, pheasants, and quail.
(adapted and modified from GAO 1999)

Antibiotics are also used in companion animals, most often for treating dermatological conditions, ear infections, respiratory infections, urinary tract infections, and wounds. Applications in companion animals are addressed in Appendix 1.