The food we eat, the animals we treat
A handout from the panel "Latest dangers, latest efforts to combat antibiotic resistance" at Health Journalism 2007.
Teresa Y. Morishita, D.V.M., Ph.D., Dipl. ACPV Professor, Poultry Medicine and Food Safety
College of Veterinary Medicine, Western University of Health Sciences Pomona, California 91766
Antimicrobial agents are widely used in agriculture, especially in animal production, to treat, prevent, and control bacterial infections as well as to promote growth and enhance feed efficiency. There is evidence that the use of antibiotics in animals can select for antimicrobial resistance in bacteria, particularly the ones inhabiting the intestinal tracts. These antimicrobialresistant organisms, including foodborne bacteria, may serve as reservoirs for antimicrobial resistance genes and infect and/or transfer these genes to humans via contaminated food of animal origin. Over the last decade, the emergence of antimicrobial resistance in Campylobaeter strains isolated from animals has increased dramatically in many countries around the world. The emergence of antimicrobial resistance in these food borne pathogens is likely due to the widespread use of antimicrobial agents in food-producing animals.
Although antimicrobial agents can be used in conventional animal production, the use of these antimicrobial substances has been restricted in organic production. Since no antimicrobials have been used in organically-raised chickens and turkeys and since the demand for organic animal produce has been increasing considerably over the last several years, the difference in antimicrobial resistance of Campylobaeter isolates from conventional and organic poultry operations as well as the association between antimicrobial usage in animal production practice and the development of antimicrobial resistance in food-borne bacterial pathogens such as Campy/obaeter jejuni is of interest. Hence, the objective of this project was to investigate the association between antimicrobial usage in chickens and turkeys in commercially-raised and organically-raised environment and the development of antimicrobial resistance in Campy/obaeter species.
The difference in quinolone and fluoroquinolone resistance rates between Campy/obaeter strains isolated from commercially-raised and organically-raised broilers and turkeys was observed in this study. Approximately 46% of Campy/obaeter strains isolated from conventionally-raised broilers and 67% of Campylobaeter strains isolated from conventionally raised turkeys were resistant to ciprofloxacin, norfloxacin, and nalidixic acid. In contrast, none of Campy/obaeter strains isolated from organically-raised broilers and less than 2% of Campylobaeter strains isolated from organically-raised turkeys were resistant to these antibiotics. Since quinolones and fluoroquinolones have never been used in these organic poultry operations, it is not surprising that little or no fluoroquinolone resistance was observed among Campylobaeter strains isolated from organic poultry farms. A high prevalence of fluoroquinolone resistance observed in Campylobaeter isolates from conventional broiler farms is interesting. Although no fluoroquinolones were used in conventional broiler flocks from which the samples were collected, it should be noted that these antimicrobial agents were used in the previous flocks of these conventionally-raised broilers. Because certain quinolone-resistant clones were stable and able to persist on the farms during several rotations even when there had been no selective pressure on that farm for a long period of time and because fluoroquinoloneresistant Campylobacter strains could outcompete fluoroquinolone-susceptible Campylobacter strains in the absence of antimicrobial usage, this may be the explanation of a high fluoroquinolone resistance rate observed among Campylobacter isolates from conventionally raised broilers. In contrast, since fluoroquinolones were used in conventional turkey operations, a high prevalence of fluoroquinolone resistance observed in Campylobacter strains isolated from conventionally-raised turkeys is not unexpected.
In summary, significant difference (P < 0.05) in quinolone and fluoroquinolone resistance rates between Campylobacter strains isolated from commercial poultry operations and organic poultry operations observed in this study suggests that the practice of fluoroquinolone usage in commercial poultry production systems can lead to the development of fluoroquinolone resistance in Campylobacter species.
Source: Luangtongkum, T., T.Y. Morishita, A. J. Ison, S. Huang, P. F. McDennott, and Q. Zhang. The Effect of Conventional and Organic Practices on Prevalence and Antimicrobial Resistance of Campylobacter in Poultry. Appl. Environ. Micro. 72:3600-3607, 2006.
