Consumers shopping for raw chicken that does not contain antibiotic-resistant E. coli are in for a difficult search, according to a research team from four separate institutions, including Northern Arizona University (NAU).

For reasons that could not be immediately explained, kosher chickens carried the greatest amount of antibiotic-resistant E. coli, while organic chicken showed antibiotic-resistant bacteria levels just as high as conventional chicken. Only chickens 'raised without antibiotics' (RWA) came in with reduced but still contaminated, levels of the E. coli 'superbug'.

The study looked at the products of various poultry production methods – kosher, organic, RWA and conventional – but not at the details of the processing methods behind them. Researchers said more study is needed, especially on kosher.

The antibiotic resistance in chicken study was released on the same day the federal Centers for Disease Control and Prevention (CDC) in Atlanta said drug-resistant superbugs are now an urgent public health danger in the United States.

The chicken researchers are from the Horace Mann Bronx Campus, Translational Genomics Research Institute of Flagstaff, NAU and George Washington University in Washington DC. Dr Bruce Hungate, director of the Ecosystem Science and Society Center, and NAU professor of biology, headed the team. The research was funded by the Merriam-Powell Center for Environmental Research and the Ecosystem Science and Society Center, both at NAU.

“We examined the occurrence of antibiotic-resistant E. coli on raw chicken marketed as conventional, organic, kosher and RWA,” the study states. “From April to June 2012, we purchased 213 samples of raw chicken from 15 locations in the New York City metropolitan area.”

The researchers then screened E. coli isolates from each sample for resistance to 12 common antibiotics.

According to the report, “Although the organic and RWA labels restrict the use of antibiotics, the frequency of antibiotic-resistant E. coli tended to be only slightly lower for RWA, and organic chicken was statistically indistinguishable from conventional products that have no restrictions.”

The study found that chicken sold as kosher had the highest frequency of antibiotic-resistant E. coli – nearly twice as high as conventional raw chicken. In the abstract for the study, authors stated that their kosher finding “belies the historic roots of kosher as a means to ensure food safety”.

Other researchers at the University of Washington, Royal Veterinary College of the United Kingdom and University of Tennessee reviewed the report, and, in a update, the researchers responded by disclosing more of their data.

“Organic, RWA, and kosher food products supply a growing market niche,” the study states. “Consumers perceive that they offer health benefits and are willing to pay a premium for them. The actual health benefits of organic foods are largely anecdotal. Little is known about the frequency of antibiotic-resistant microorganisms on kosher products.”

USDA requires specific production methods for organic and RWA products, while kosher (and halal) production methods are religious requirements. To carry an RWA label, poultry must be raised continuously under organic management and without the use of antibiotics from “birth to harvest.”

The study found that strains of E. coli isolated from samples in the RWA category tended to be resistant to fewer drugs “but the difference was not significant versus conventional and organic, which did not differ from each other”.