The problem of antimicrobial resistance (AMR) is growing in the United States and worldwide. This report explores the scope of the AMR problem and what can or should be done about AMR from the standpoint of animal agriculture.
The problem of antimicrobial resistance (AMR)s growing in the United States and worldwide. The questions posed by the Commission were several: What is the scope of the AMR problem? What is the contribution of industrial animal agriculture to the problem? What is the history of and reasons for the use of antimicrobials in animal agriculture? What can or should be done about AMR from the standpoint of animal agriculture?
It is difficult to calculate the scope of the AMR problem as it relates to animal agriculture because of the types of surveillance that are in place and the way that AMR is transmitted between bacteria. Only certain infectious bacteria are tracked by the Centers for Disease Control and Prevention (CDC) and state and local health agencies. Other types of bacteria, some infectious and some not, are not tracked, so only a certain cross section of the possible resistant microbes are seen by the tracking agencies. This is a problem because of the way resistance is spread between capable bacteria. These bacteria have a small "cassette" of genes that they transmit to each other in one piece. These cassettes can contain resistance to more than one antimicrobial, rendering formerly unexposed or nonresistant bacteria suddenly resistant to multiple kinds of antimicrobials. In addition, bacteria that are not tracked can still transmit resistance elements. For example, many bacteria live in the human digestive tract or on human skin. These are not normally harmful (and are often helpful) and are not monitored. However, these harmless bacteria may still be capable of passing resistance to other bacteria that are harmful, or could then become harmful.
Exposure of bacteria to antimicrobials exerts a selective pressure, killing susceptible bacteria and allowing resistant ones to survive and reproduce. Sir Alexander Fleming, the father of antibiotics, described the phenomena of antibiotic resistance and suggested in the 1940s that extensive use of antibiotics would cause bacteria to develop resistance, and further pointed out that new antibiotics would be necessary to combat this on a regular basis. While it is difficult to measure what percent of resistance is caused by antimicrobial use in agriculture, as opposed to other settings, it can be assumed that the wider the use of antibiotics, the greater the chance for the development of antibiotic resistance.
Antibiotics were first used in the early 1950s as a growth promoter in food animals. As "resistance" developed and the antibiotics lost their ability to promote growth in the animal, new generations of antibiotics and antimicrobials were used. Today, estimates vary on the amounts of antimicrobials that are used in food animal production, as well as the amounts that are used nontherapeutically versus therapeutically.
Antimicrobials can save lives of humans and animals, but must be used judiciously given their biological properties. The greater the amount of antimicrobials present in the general environmental pool, the greater the pressure for the development of resistance within many different bacterial populations. Animal agriculture industry representatives have recognized this in statements to the Commission. This report was commissioned to expand on these concepts.
Aarestrup, FM, Y Agerso, et al. (2000). “Comparison of antimicrobial resistance phenotypes and resistance genes in Enterococcus faecalis and Enterococcus faecium from humans in the community, broilers, and
pigs in Denmark.” Diagn Microbiol Infect Dis 37(2):127-37.
Aarestrup, FM, AM Seyfarth, et al. (2001). “Effect of abolishment of the use of antimicrobial agents for growth promotion on occurrence of antimicrobial resistance in fecal enterococci from food animals in Denmark.” Antimicrob Agents Chemother 45(7): 2054-9.
Alekshun, MN and SB Levy (2006). “Commensals upon us.” Biochem Pharmacol 71(7): 893-900.
Anderson, ME and MD Sobsey (2006). “Detection and occurrence of antimicrobially resistant E. coli in groundwater on or near swine farms in eastern North Carolina.” Water Sci Technol 54(3): 211-8.
Barber, M, FG Hayhoe, et al. (1949). “Penicillin-resistant staphylococcal infection in a maternity hospital.” Lancet 2(25): 1120-5.
Bartholomew, MJ, DJ Vose, et al. (2005). “A linear model for managing the risk of antimicrobial resistance originating in food animals.” Risk Anal 25(1): 99-108.
Barza, M. and K. Travers (2002). “Excess infections due to antimicrobial resistance: the ‘Attributable Fraction'.” Clin Infect Dis 34 Suppl 3: S126-30.
Bengis, RG, FA Leighton, et al. (2004). “The role of wildlife in emerging and re-emerging zoonoses.” Rev Sci Tech 23(2): 497-511.
Berge, AC, DA Moore, et al. (2006). “Prevalence and antimicrobial resistance patterns of Salmonella enterica in preweaned calves from dairies and calf ranches.” Am J Vet Res 67(9): 1580-8.
Billy, TJ and IK Wachsmuth (1997). “Hazard analysis and critical control point systems in the United States Department of Agriculture regulatory policy.” Rev Sci Tech 16(2): 342-8.
Boerlin, P, R Travis, et al. (2005). “Antimicrobial resistance and virulence genes of Escherichia coli isolates from swine in Ontario.” Appl Environ Microbiol 71(11):6753-61.
Bywater, RJ (2004). “Veterinary use of antimicrobials and emergence of resistance in zoonotic and sentinel bacteria in the eu.” J Vet Med B Infect Dis Vet Public Health 51 (8-9): 361-3.
Capitano, B, OA Leshem, et al. (2003). “Cost effect of managing methicillin-resistant Staphylococcus aureus in a long-term care facility.” J Am Geriatr Soc 51(1): 10-6.