The truth about E. coli and cattle feed

We have seen some recent outbreaks of Escherichia coli O157:H7, the common pathogenic strain of the common gut bacterium, in the human food supply, most notably in spinach last fall.

Since then, it has been common to see assertions in the mainstream media (e.g. by the quite knowledgeable food industry writer Michael Pollan) that E. coli O157 is purely a product of the mega-feedlot industry, because the pathogen is not found in the guts of grass-fed cattle. It is a very attractive assertion to those of us who support a trend away from factory farms, which are demonstrably less healthy both to humans and the environment in many ways. So, I thought it would be worthwhile to investigate this further.

Buried within a forest of “green” sites promoting this idea was a link by a commenter to a brief Kansas State news release claiming that this assertion was false. Dr. David Renter, assistant professor of veterinary epidemiology at KSU, has done research himself on this important human health topic and has studied the prevalence of E. coli O157 not only in feedlot vs. range-fed cattle, but in wildlife as well.

In Renter et al., 2003, he and his colleagues found E. coli O157 in 2.48% of fecal samples from rangeland cattle in Kansas and Nebraska, similar to a rate found in previous studies of “confined” (=feedlot) cattle. They also tested several hundred samples from wildlife, including coyotes, whitetailed deer, raccoons, and possums. In wildlife, the pathogen was only found in one possum sample.

An earlier study (Renter et al., 2001) confirmed the presence of E. coli O157 in fecal samples from wild deer in Nebraska, albeit at the very low rate of 0.25% (a rate of 25 out of 10,000).

Surpirsingly, Kudva et al. (1997) found, in sheep, the opposite trend I expected to see based on media reports on cows. Animals were innoculated with E. coli O157, then fed one of two diets: grass hay, or corn and alfalfa. In this case, grass-fed sheep were shedding bacteria twice as long as corn/alfalfa-fed sheep.

So where did the grain vs. grass theory come from? It turns out it was from a Science paper in 1998 by Diez-Gonzalez et al., which did not specifically address pathogenic E. coli. As explained by Gannon et al. (2002):

A grass diet would certainly be expected to cause a change in the intestinal microflora as well as parameters such as volatile fatty acid species and concentrations and the pH of the digesta. A recent study has shown that grain feeding selects for acid-resistant E. coli strains and that feeding Timothy hay rapidly reduces the numbers of these organisms shed in the faeces… While this appears to be the case, the authors of this somewhat controversial study failed to demonstrate that E. coli O157: H7 was one of the acid-resistant E. coli strains selected for by grain feeding and reduced by hay feeding. Recent studies by Hovde and colleagues … showed that hay feeding increases rather than decreases faecal shedding of E. coli O157: H7 by beef cattle which were orally inoculated with the organism.
… In addition, naturally occurring antimicrobial substances in certain plants may play a role in faecal shedding of the organism by cattle; e.g. Duncan and colleagues have shown that certain coumarins derived from plants inhibit growth of E. coli O157: H7.

So, once again, complex nuances in a biological system fail to penetrate the aura of the either-or dichotomy so loved by the media.

There is no doubt that the relationship between E. coli, domesticated animals, and husbandry methods is not simple. As Renter et al. (2003) state:

The observed number of E. coli O157 XbaIPFGE subtypes, the frequency and persistence of specific subtypes, and the presence of indistinguishable subtypes in cattle, water, and wildlife indicate that the molecular epidemiology of E. coli O157 in range cattle production environments is complex. A clear description of the complex molecular epidemiology requires explicit definition of factors related to the molecular biology and micro- and macroecology of the organism.

The “subtypes” to which they refer number, in this study alone, 70 of just the O157 strain that they were studying. Many more exist. There are lots of possible ways to address the likely growing E. coli problem. Antibiotics are one, but there are of course problems with resistance there (Flucky et al., 2007). Hopefully, environmentally friendly rearing practices will be part of the solution, but it is clear they would not be a complete solution. E. coli O157, wherever and whenever it came from, will be with us for the duration. The question is, can we use prevention to keep it to a level that was shown in the wild deer (0.25%), or are we going to try to medicate it out of the system?

It would be wonderful if mass food supply problems had simple management answers - not that conversions of half our cattle back to pasture from feedlots would be easy. There are serious problems with our food supply, and we need aggressive journalists to be informing the public about agribusiness practices that should be changed in order to avoid major public health consequences - the recent melamine pet food scandal is a prime example of where both regulation and enforcement are severely lacking.

We need Michael Pollan and others like him to be watching out for us. But they must make absolutely sure that their credibility remains intact, because we need to know that they are more trustworthy sources than government and corporate spokesmen with obvious agendas. We need someone to be telling us the truth. So either the journalists must improve their scientific literacy enough to do the appropriate research for their story, or they must hire someone who has it already.

(Mr. Pollan, if you are hiring, I am available for freelance work.)

References:

Diez-Gonzalez F, Callaway TR, Kizoulis MG, Russell JB. (1998) Grain feeding and the dissemination of acidresistant Escherichia coli from cattle. Science, 281, 1666–8.

Fluckey, W.M., Loneragan, G.H., Warner, R. & Brashears, M.M. (2007) Antimicrobial drug resistance of Salmonella and Escherichia coli isolates from cattle feces, hides, and carcasses. Journal of Food Protection, 70, 551-556.

Gannon, V.P.J., Graham, T.A., King, R., Michele, P., Read, S., Ziebell, K. & Johnson, R.P. (2002) Escherichia coli O157: H7 infection in cows and calves in a beef cattle herd in Alberta, Canada. Epidemiology and Infection, 129, 163-172.

Kudva, I.T., Hunt, C.W., Williams, C.J., Nance, U.M. & Hovde, C.J. (1997) Evaluation of dietary influences on Escherichia coli O157:H7 shedding by sheep. Applied and Environmental Microbiology, 63, 3878-3886.

Renter, D.G., Sargeant, J.M. & Hungerford, L.L. (2004) Distribution of Escherichia coli O157: H7 within and among cattle operations in pasture-based agricultural areas. American Journal of Veterinary Research, 65, 1367-1376.

Renter, D.G., Sargeant, J.M., Oberst, R.D. & Samadpour, M. (2003) Diversity, frequency, and persistence of Escherichia coli O157 strains from range cattle environments. Applied and Environmental Microbiology, 69, 542-547.

Tags: ecology, health

This entry was posted on Friday, May 4th, 2007 at 10:36 pm and is filed under ecology, environmental toxins, health. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.