Poultry Workers Carry Resistant Bacteria

By Sangita Viswanathan

They are much more likely to harbor antibiotic-resistant E. coli

Antimicrobial use in food animal production has long been a cause for concern. While antimicrobials have been widely used for therapy, prophylaxis, and growth stimulation in broiler chickens, their use has been linked to the emergence and spread of antimicrobial-resistant enteric bacteria. Currently, 16 antimicrobial drugs are approved for use in poultry production in the United States; reportedly, gentamicin is the most widely used.

A recent study by researchers at the Johns Hopkins Bloomberg School of Public Health (Baltimore) has found, however, that poultry workers were 32 times more likely to carry E. coli bacteria resistant to gentamicin than those working in other areas.

Published in the December 2007 edition of Environmental Health Perspectives, the study results suggest that the food processing environment plays a critical role in the spread of antibiotic-resistant bacteria.

The study indicates that, for antibiotic-resistant bacteria, occupational exposure may be an important entry point into the general community, says Lance B. Price, MS, the study’s lead author. Price serves on the research faculty at the Johns Hopkins School of Medicine, Division of Infectious Disease, and is a scientific adviser to the Johns Hopkins Center for a Livable Future.

Shift in Production

Price and other researchers note that as food animal production has shifted from the independent farmer to large-scale, industrialized operations, the use of antimicrobials in feeds intended to stimulate growth has increased. More than half the antimicrobial drugs produced in the United States are used in food animal production. In the United State, more than 9 billion food animals are produced annually.

“Such antibiotic use in food animal production provides a foundation for the evolution of antibiotic-resistant bacteria, and these bacteria can readily colonize people through the environment,” for example, in contaminated water “and occupational exposures,” Price says. He hopes the study results may lead some regulators to reconsider whether to allow lifesaving antibiotics to be used for non-therapeutic purposes in animal production facilities.

The study was conducted with poultry workers and community residents in the eastern shore regions of Maryland and Virginia, among the top producers of broiler chickens in the United States (more than 600 million chickens annually). Researchers conducted in-depth analyses of 49 study participants—16 in the poultry industry and 33 community residents. Stool samples from the participants were tested for resistance to the antimicrobials ampicillin, ciprofloxacin, ceftriazone, gentamicin, and tetracycline.

The researchers say similar results have been published in Europe. They add that human exposure to antimicrobial-resistant bacteria through food has been examined much more extensively than exposure through occupational and environmental routes.

“We have to take strong measures on a global scale in order to curb the emergence of pan-resistant bacterial pathogens,” Price says. “One of the first places to start is restricting antibiotic use in food animal production. I wish I could say that the U.S. was taking the lead on this issue, but I’m afraid our government representatives are doing more to hinder progress than to help.”

Limited Scope

But Donald E. Conner, PhD, professor and head of the poultry science department at Auburn University (Auburn, Ala.) feels this study will have little impact on the industry because of what he describes as its limited scope.

“While findings of this study add to the discussion on agricultural uses of antibiotics, they fall short in defining changes. In fact, for five of the six targeted antimicrobials, there was no difference in isolation of resistant E. coli between the two population groups, and gentamicin is not a major antimicrobial in the treatment of serious human illness,” says Dr. Conner, who is also on the panel of experts for the Poultry Science Association (Savoy, Ill.).

Total antimicrobial use in animal agriculture is difficult to estimate, says Dr. Conner, citing the 2002 study “The Role of Antibiotics in Agriculture” from the American Academy of

Microbiology (Washington, D.C.). “Also,” notes Dr. Conner, “when Price and his co-authors claim that gentamicin is the most widely used antibiotic in the poultry industry, it is used only on a high percentage of newly hatched or pre-hatched chicks, and the volume used is very low.”

Dr. Conner feels that as science advances, sound risk-benefit decisions will evolve. Already, some companies are reducing antimicrobial use in response to consumer demand, he adds.