So hi. Apologies to disappear, constant readers — I was mired in the last revise of a big magazine story (which will be out in two months and will be very exciting). Back now, and catching up. Here’s something that caught my eye yesterday, on a topic that I haven’t looked at since this blog was at its former home: the issue of ethanol-manufacturing leftovers, and whether they contribute to antibiotic resistance in the animals they are fed to.
Quick background: Making ethanol is a lot like brewing beer. You take a starchy carbohydrate, wet it down to make a mash, warm it up, add yeast, and wait. To fuel its reproduction, the yeast digests the carbohydrate; as waste products, it respires carbon dioxide and produces alcohol. (So basically beer is yeast pee, but let’s not get off track.)
When the process is scaled up, it’s common for the ethanol mash to become contaminated with Lactobacilli, which compete with the yeast for the sugars in the mash but, instead of producing alcohol, leave behind lactic acid. That lowers the ethanol yield from a batch, sometimes as much as 5 percent — a lot, for an industry whose profit margins are thin — and so ethanol producers routinely inoculate the mash with antibiotics to control the competition.
This would not be important, except that selling the leftover mash is a key contribution to making ethanol profitable. The mash is renamed “distillers’ grains” and is sold as feed for beef and dairy cattle and for chickens.
Perhaps you begin to perceive the problem: If antibiotics were used in the mash, the possibility exists that some low dose of antibiotics will remain in the grains, and will be consumed by the livestock. That makes the distillers’ grains functionally similar to standard feed containing low doses of antibiotics for growth promotion/feed efficiency, a practice blamed for promoting the development of antibiotic-resistant organisms.
In fact, in 2008, the Food and Drug Administration said it had tested ethanol leftovers from around the country and found residues of four common antibiotics: penicillin and erythromycin; tylosin, a veterinary antibiotic; and virginiamycin, a veterinary antibiotic similar to the human-medicine drug combination quinupristin-dalfopristin or Synercid. (The FDA apparently never published that research, though it talked about it in an AP story; Tom Philpott also covered it when he was at Grist.)
Which brings us to the new news. Researchers from the University of Minnesota have announced an analysis of antibiotic residues in distillers’ grains. The results haven’t brought much clarity, though; in fact, what you see in them seems to be determined by where you stand on this issue from the start.
According to a piece in National Hog Farmer:
Devan Paulus, a graduate student working with Jerry Shurson, swine nutritionist at the University of Minnesota, collected 20 distiller’s (wet) grains with solubles (DGS) samples and 20 distillers’ dried grains with solubles (DDGS) samples from various ethanol plants throughout the United States. The samples, collected quarterly for a year, were analyzed for virginiamycin, erythromycin, penicillin, tetracycline and tylosin residues. Further testing on E. coli and Listeria monocytogenes sentinel bacteria revealed whether the residues were active.
While all of the 117 samples tested to date contained antibiotic residues, only one sample was found to have an antibiotic residue active enough to inhibit E. coli growth. The residue concentrations in the distillers’ grains are much lower than minimum-approved Food & Drug Administration (FDA) feed levels for finishing swine. “Extremely low concentrations of penicillin (less than 0.2 ppm), erythromycin (less than 1 ppm), tetracycline (less than 0.008 ppm) and tylosin (less than 0.02 ppm) residues were detected in wet and dried distillers’ co-products,” Shurson explains. “Only two of the 117 samples contained low, but detectable, concentrations (0.5 and 0.6 ppm) of virginiamycin residues, but this level is well below the 1 ppm FDA GRAS approval level,” Shurson explains.
(Note: This research has apparently not been published, but Devan Paulus kindly confirmed by e-mail that the excerpt above describes the results accurately.)
National Hog Farmer‘s take on the results is captured in its headline: “Co-Product Antibiotic Levels Nearly Nil.”
The Institute for Agriculture and Trade Policy, which published a report in 2009 examining antibiotic resistance from distillers’ grains, disagrees with that rosy assessment. In a post analyzing the story, Julia Olmstead says:
[L]ow-level antibiotic activity is a pathway to antibiotic resistance, as the antibiotics kill off susceptible bacteria leaving the “superbugs” to thrive. Even one sample in 117 testing positive for antibiotic residue is an indication that we don’t know the fate of these antibiotics or if they’re contributing to the antibiotic resistance epidemic.
Perhaps the most frustrating aspect of this issue is that these antibiotics are not necessary. Effective non-antibiotic antimicrobials are readily available to producers and used successfully by many producers, including POET, the largest producer in the country. According to POET, the switch to antibiotic-free distillers’ grains offered a market advantage: antibiotic residues are not permitted in layer hen feed.
This is frustrating, because it feels so familiar: The distillers’ grains issue seems mired in the same sort of he-said-she-said that has afflicted growth-promoter antibiotic use for decades. (“Contributes to antibiotic resistance!” “Enhances herd health!”)
Clearly some substantial hard data is needed — and might be on the way. Following those 2008 tests, the FDA actually started a project sampling distillers’ grains from around the United States. And in its planned actions for this year, the agency has included a “draft guidance” specifically on the antibiotic-residue problem. Maybe some clarity is coming.
