With growing concern over antibiotic resistance, public health advocates have long pushed for more responsible use of these drugs — both in human medicine and animal agriculture — but there is one piece of the antibiotics puzzle that has not received as much attention: ethanol production.

Last week, Reps. Ed Markey (D-MA) and Louise Slaughter (D-NY) wrote to the U.S. Food and Drug Administration asking some tough questions about the potential link between ethanol byproducts in animal feed and antibiotic-resistant bacteria.

“Antibiotic-resistant strains of bacteria are a grave public health threat that is growing worldwide,” wrote Markey and Slaughter. “As the threat of antibiotic resistance expands, we must ensure that the unnecessary use of antibiotics in agricultural animals is minimized and FDA has the ability to limit their use if it serves to protect public health.”

cornpile_iphone.jpgThe letter follows a new report by Minneapolis-based Institute for Agriculture and Trade Policy, which highlights the fact that many ethanol producers routinely add antibiotics like medically important penicillin and erythromycin, as well as virginiamycin and tylosin, when mixing corn mash and warm water to ferment the ethanol.

Producers use antibiotics to keep the tanks from being contaminated with Lactobacilli, bacteria that compete with the yeast and lowers the ethanol yield. Contamination is common so tanks are often inoculated as a preventative measure.

So, what does this process have to do with food safety and antimicrobial resistance? Well, the leftover distillers grains can contain antibiotic residues and they are routinely fed to food animals.

As IATP points out in their new paper, “Bugs in the system,” ethanol producers have no restrictions on antibiotic use: “Ethanol producers have full discretion over the quantity and frequency with which they dump antibiotics into their plants. As ethanol production has exploded, from 4.5 to 12.5 billion gallons per year between 2005-06 and 2009-10, antibiotic use also has undoubtedly increased, although currently the FDA does not appear to track antibiotic sales to ethanol producers, as it does sales for use in animals.”

In the last 10 years, distillers grains production has skyrocketed from, from 2.5 to 34.1 million metric tons per year according to the report. Around 41 percent of the byproduct is used in domestic beef production, 26 percent in dairy, 5 percent go to swine and poultry, and 22 percent heads overseas for livestock feed.

There is not a lot of data on antibiotics residues in distillers grains and it’s not clear whether the byproduct might be contributing to antibiotic resistance.

In 2008, FDA tested and analyzed 45 samples of distillers grains and found antibiotic residues in 24 (53 percent) of them, including some over .5 parts per million (ppm).

“These test results were exceedingly important because they disproved the belief that antibiotic use in ethanol production was benign vis-à-vis public health,” argues IATP in the paper. “This study showed the opposite: Antibiotic use in ethanol production increases the load of nontherapeutic antibiotics being fed to livestock, which the FDA itself acknowledges is a public health threat needing to be addressed.”

In 2010, FDA conducted another round of sampling. Out of 46 total samples, 28 of which were domestic and 18 imported, four tested positive for residues in concentrations ranging from .16 to .58 ppm.
The question is whether these levels are significant.

The study cites a new paper out of FDA’s Center for Veterinary Medicine that analyzed the 2010 findings. Researchers found that the lowest levels of penicillin and virginiamycin present in the samples didn’t contribute to antibiotic resistance among Campyloacter or Enterococcus bacteria. But they also found that Erythromycin at .58 ppm did select for resistance in enteroccous bacteria.
“Given these results it is suggested that residues in distillers grains be more fully evaluated given the importance of this antimicrobial in clinical medicine,” the researchers wrote in their abstract.
Recent research out of the University of Minnesota, which has not yet been published, found antibiotic residues in all of the 117 samples they tested and one result was strong enough to inhibit E. coli growth.

IATP argues that distillers grains containing antibiotics should be regulated as food additives and regulated by FDA. The paper recommends that FDA ban the sale of unapproved antibiotics to ethanol producers and asks that the ethanol industry voluntarily switch to effective non-antibiotic antimicrobial alternatives. According to some estimates, half the industry already has already done this.

The paper also recommends that the U.S. Department of Agriculture, the Department of Energy and state and federal agencies help the industry make the switch with technical assistance and financial support.

In their letter to FDA, Markey and Slaughter seek specific responses to several of the issues raised in the IATP report.

They want to know why FDA hasn’t published the full results of its 2008 survey on distillers grains and antibiotic residues and ask whether the survey results suggest that these residues could also be found in meat, poultry, dairy or egg products.

The lawmakers further ask, “Does FDA believe that the presence of antibiotics in DGS used for livestock feed may pose a similar public health concern as the impact of directly using antibiotic drugs to promote livestock growth?”

Markey and Slaughter also ask why the agency banned the use of distillers grains contaminated with certain antibiotics for laying hens but not for other food producing animals.

The letter is available here.