Elevated Risk of Carrying Gentamicin-Resistant Escherichia Coli among U.S. Poultry Workers

Article excerpt

Antimicrobial-resistant bacteria including Escherichia coli are common contaminants of the industrial broiler chicken environment (Hayes et al. 2004; Khan et al. 2005). Studies conducted in Europe indicate that poultry growers and poultry-house workers are at risk of exposure to these and other pathogens (Ojeniyi 1989; van den Bogaard et al. 2001). Similar studies must be conducted in the United States in order to measure occupational exposure to antimicrobial-resistant E.coli in the U.S. broiler chicken industry.

Antimicrobial use has been integral to the industrialization of food-animal production. Over the past half century, food-animal production has changed from a largely entrepreneurial system run by independent farmers to an industrial mode of production in which a small number of companies control all aspects of production, from breeding and feed formulation to slaughter and distribution of consumer products. This shift in both the organization and methods of production has allowed for the reliable, high-throughput production of food animals on a scale not seen in human history. In the United States alone, > 9billion food animals are produced annually (U.S. Department of Agriculture 2004). Antimicrobials have been used in food-animal production since the early days of their discovery (Viola and DeVincent 2006). Although exact figures are unavailable, it is currently estimated that at least half of all of the antimicrobials consumed in the United States are used in food-animal production (Steinfeld etal. 2006). Antimicrobials are used for multiple purposes including outbreak control, prophylaxis, and growth promotion. The antimicrobials approved for use in the U.S. food-animal industry include many drugs of critical importance to human medicine. Sixteen antimicrobial agents from 10 antimicrobial classes are currently approved for use in U.S. poultry production (Appendix 1). Among these, gentamicin (GEN) is reported to be the most commonly used antimicrobial (Luangtongkum etal. 2006).

Appendix 1. Antimicrobial agents approved for use in broiler production
(adapted from the National Research Council 1999).

Antimicrobial class    Agent

Aminocoumarin        Novobiocin
Aminocyclitols       Spectinomycin (a)
Aminoglycosides      Streptomycin
                     Neomycin
                     Gentamicin
[beta]-Lactams       Penicillin (a)
Decapeptides         Bacitracin (a)
Lincosamides         Lincomycin
Macrolides           Erythromycin
                     Tylosin  (a)
                     Oleandomycin (a)
Organoarsenicals     Roxarsone
Phosphoglycolipids   Bambermycin (a)
Streptogramins       Virginiamycin (a)
Tetracyclines        Chlortetracycline (a)
                     Oxytetracycline
                     Tetracycline

(a) Labeled as growth promoter

The use of antimicrobials in industrial food-animal production selects for antimicrobial-resistant bacterial populations. Antimicrobial-resistant bacteria have been detected in animal wastes (Jindal et al. 2006), animal bedding (Kelley et al. 1998), air both inside (Chapin et al. 2005) and downwind (Gibbs et al. 2006) of animal feeding operations, in groundwater near animal feeding operations (Anderson and Sobsey 2006), and in consumer meat and poultry products (Food and Drug Administration 2006). There is substantial evidence that antimicrobial use in food-animal production contributes to the burden of antimicrobial-resistant diseases in human populations through foodborne routes of exposure.

Examples include infections with fluoro-quinolone-resistant Campylobacter (Gupta et al. 2004), vancomycin-resistant Enterococci (VRE) (Bonten et al. 2001), multidrug-resistant Salmonella (Molbak 2006), and multidrug-resistant E. coli (Ramchandani et al. 2005). Additional pathways likely exist through exposure to contaminated environmental media in and around animal production facilities as well as contact with animals in the occupational setting. …