Escherichia coli and Grassfed Beef

Escherichia coli (E. coli), is a ubiquitous bacteria in our environment, but a specific strain, 0157:H7, can cause serious human illness and even death.

It has been estimated that 89% of ground beef patties in the United States contain E. coli 0157:H7 (USA Today 3/2/2000).  Contamination by E. coli takes place in the slaughterhouse when manure or undigested stomach material from an animal infected with E. coli comes in contact with meat.  Studies show that only half of the meat and poultry involved in U.S. recalls (primarily for pathogen contamination) from 1998-2002 was actually recovered by its manufacturers (Teratanavat and Hooker 2004).

Our small family processor is committed to clean, individual processing.  He does not use assembly lines.  He pays attention to details.  In addition, research suggests grass fed cattle have much lower (in some studies nearly nonexistent) rate of infection with E. coli (Jonsson et al 2001).

Jonsson, M.E. et al. 2001.  Persistence of Verocytotoxin-Producing Escherichia Coli 0157:H7 in Calves Kept on Pasture and in Calves Kept Indoors.  International. Journal of  Food Microbiology 66: 55-61.

Staff.  2000.  Most ground beef tainted with E. coli,” USA Today, 2 Mar 00. Quote from Mark Powell, USDA/FSIS.

Teratanavat, R. and N.H. Hooker.  2004. Understanding the characteristics of US meat and poultry recalls: 1994–2002 Food Control 15:359-367.

LINKS AND ADDITIONAL READING

Jo Robinson has done the most to bring together the information on the relationship of E. coli and grain-finishing of beef.  Here are two articles from her website.  You can read more in her excellent book “Why Grassfed is Best” and at her website EAT WILD.

The deadliest form of E. Coli is more common than originally thought. Fortunately, grassfed animals are much less likely to transmit the disease.

A study in the March 28th, 2000 issue of the Proceedings of the National Academy of Sciences reports that as many as one out of every three cattle may play host to the deadliest strain of E. coli bacteria ( 0157:H)   This is ten times higher than earlier estimates.

As explained in more detail in Why Grassfed Is Best feeding cattle their natural diet of grass instead of grain greatly reduces the risk of disease transmission.  Why?  First, it keeps the overall bacteria count low.  Second, it prevents the bacteria from becoming acid resistant. Acid-resistant bacteria are far more likely to survive the acidity of our normal digestive juices and cause disease.  The first graph below illustrates the absolute numbers of E.Coli bacteria found in grassfed versus grainfed animals.  The second graph shows how many of the bacteria are likely to withstand our gastric juices.  (Note: Grassfed animals have so few acid-resistant bacteria that the number fails to register on the scale of the graph.)

One of the lead researchers on the project, USDA microbiologist James Russell, told a reporter for Science Magazine, “We were absolutely shocked by the difference. We never found an animal that didn’t agree with the trend.”

You should still take the normal precautions when handling and cooking grassfed meat, however.  As few as ten E.Coli bacteria can cause disease in people with weakened immune systems.

(Diez-Gonzalez, F., et al. (1998). “Grain-feeding and the dissemination of acid-resistant Escherichia coli from Cattle.” Science  281, 1666-8.)

 

Hay feeding does indeed reduce acid-resistant E. coli, says Nebraska Beef Report.

In 1998, researchers Diez-Gonzalez and colleagues from Cornell University drew worldwide attention when they reported that switching cattle from grain to grass lowered the production of acid-resistant E. coli bacteria.  Acid-resistant E. coli are believed to be much more difficult for humans to combat.  The fact that keeping animals on pasture might protect consumers from E. coli was very good news, indeed.

Since publication of the Cornell study, however, these results have been contested by a number of groups, including researchers at the University of Idaho.  Now a study by the USDA Meat and Animal Research Center in Lincoln, Nebraska supports the Cornell findings. The Nebraska researchers began their investigation by trying to find alternative feeding strategies to combat acid-resistant E. coli, contending that hay feeding “is not a practical approach for cattle feeders.” Unfortunately, none of their experimental approaches worked.  When they switched the animals to hay, however, they found that the more natural diet did indeed have the desired effect. The researchers concluded: “This study confirms Diez-Gonzalez (1998) report that feeding hay for a short duration can reduce acid-resistant E. coli populations.”  Score one for Mother Nature.

 

(“Influence of Diet on Total and Acid Resistant E. coli and Colonic pH.” Tony Scott, Klopfenstein, T., et al.” 2000 Nebraska Beef Report, pages 39-41.

FDA Grant FD-R-00157601 (September 29, 1998 – September 30, 2000)

Factors affecting numbers of acid-resistant Escherichia coli in cattle

Dr. James B. Russell

USDA/ARS

Ithaca, NY

Background:

1999. coli O157:H7, an acid resistant strain of E. coli that causes food-borne illness in humans, can enter the human food supply from cattle via fecal contamination of beef carcasses at slaughter. Previous attempts to correlate the incidence of E. coli O157:H7 with specific diets or feeding management practices yielded few statistically significant or consistent findings. However, cattle diets may be changed to decrease fermentation acid accumulation in the colon. When fermentation acids accumulate in the colon and pH decreases, the numbers of acid-resistant E. coli. increase, and acid-resistant E. coli are more likely to survive the gastric stomach of humans. In cattle fed hay for a brief period (< 7 days), acid-resistant E. coli numbers declined dramatically. Pure culture studies indicate that extreme acid resistance is triggered by either un-dissociated fermentation acids or amino acids. If E. coli cultures are grown in rich culture medium the acid-resistance is already so high that fermentation acids are without effect. Because other workers have show that brief periods of hay feeding can decrease the number of cattle shedding E. coli O157:H7 (Keen, et al. 1999, 80th Conference of Research Workers in Animal Diseases, Abstract #86, November 7-9, 1999. Chicago, Ill.), it appears that cattle feeding management practices can be manipulated to decrease the risk of food-borne illness from E. coli.

The four specific aims of the research in this grant proposal included:

1. Conduct of cattle feeding trials to monitor the effects of grain and feed additives on the numbers of acid-resistant E. coli and define more precisely the colon pH and volatile fatty acid concentration needed to trigger the acid resistance of E. coli, in vivo.

Results: Acid resistant E. coli counts increased exponentially when the undissociated volatile fatty acids concentrations in the colon were greater than 0.1 mM.

2. Experimentation to determine if dietary-dependent differences in E. coli acid-resistance persist in raw hamburger.

Results: Acid resistant colonic E. coli from cattle fed grain persisted in raw hamburger for 7 days in the refrigerator. Acid-resistant E. coli could not be detected in hamburger that been inoculated with feces from cattle fed hay.

3. Monitoring of the acid resistance, colicin production and genetic diversity of E. coli strains isolated from cattle fed different diets.

Results: The diversity of E. coli in cattle was very large (at least 22 genotypes). and animal variation was as great as diet dependent differences. None of the predominant E. coli strains produced colicins and inhibited E. coli O157:H7.

4. Determination of the effects of pH, volatile fatty acids, oxidation-reduction potential and nutrient starvation on E. coli O157:H7.

Results: In vitro studies indicated that the acid resistance of E. coli was induced by undissociated volatile fatty acids, and this induction could be triggered by either an increase in total concentration or a decrease in pH. When E. coli was cultivated in vitro under reducing conditions (low redox) more volatile fatty acids were needed to induce extreme acid-resistance. Stationary phase (starved) were more acid-resistant than those that were growing on glucose.

Overall Conclusions

Given the observation that grain-based cattle diets can increase the acid resistance of E. coli in vivo, and promote E. coli O157:H7 shedding, there is still a need for dietary manipulation. Diet shifts (grain to hay for 5 days) have decreased E. coli resistance and E. coli O157:H7 shedding, but additional research is needed to see if other less drastic changes in diet can achieve the same effect.

Published findings based on this FDA supported research:

Diez-Gonzalez, F., and J. B. Russell. 1999. Factors affecting the extreme acid-resistance of Escherichia coli O157:H7. Food Microbiol. 16:367-374.

Jarvis, G. N., M. G. Kizoulis, F. Diez-Gonzalez, and J. B. Russell 2000. The genetic diversity of predominant Escherichia coli strains isolated from cattle fed various amounts of hay and grain FEMS. Microbiol. Ecol. 32:225-233.

Russell, J. B., F. Diez-Gonzalez, and G. N. Jarvis 2000. Effects of diet shifts on Escherichia coli in cattle. J. Dairy Sci. 83:863-873.

Jarvis, G. N., and J. B. Russell 2001. Differences in Escherichia coli culture conditions can have a large impact on the introduction of extreme acid resistance. Curr. Microbiol. 43:215-219.

FURTHER READING:

Diez-Gonzalez, F., T. R. Callaway, M. G. Kizoulis, and J. B. Russell. 1998. Grain feeding and the dissemination of acid-resistant Escherichia coli from cattle. Science. 281:1666-1668.

Russell, J. B., and F. Diez Gonzalez 1999. Cattle, Hay and E. coli-The Response Science. 284:52-53.

Russell, J. B. 2000. Hay, grain and E. coli revisited. ASM News. 66:1.

Russell, J. B., F. Diez-Gonzalez, and G. N. Jarvis 2000. Potential effect of cattle diets on the transmission of pathogenic Escherichia coli to humans. Microbes and Infection. 2:45-53.

Russell, J. B., and G. N. Jarvis 2000. Practical mechanisms for interrupting the oral fecal lifecycle of Escherichia coli J. Molecular Microbiol. and Biotechnol. (in press).