February 2, 2011

Understanding foodborne microbial hazards for smarter food policies

Dave Love

Dave Love

Associate Scientist, Public Health & Sustainable Aquaculture Project

Johns Hopkins Center for a Livable Future

One in six Americans contracts a foodborne illness each year (CDC). Such illness can mean an unpleasant day of vomiting, diarrhea, fever, and/or worse— hospitalization or death in rare cases. “There’s something that can be said about the problem of foodborne illness, that can’t be said of many other public health problems of the day” said Elisabeth Hagan, Under Secretary for Food Safety at USDA, who opened a January 25th foodborne hazards conference convened at the Pew Charitable Trusts offices in Washington DC, “and that is: Foodborne illness is preventable.

The day-long conference “Managing the Risk of Foodborne Hazards: STECs and Antibiotic-Resistant Pathogens” was organized jointly by Pew and the Center for Science in the Public Interest (CSPI). Hagan and other conference speakers focused their attention on antibiotic-resistant pathogens and shiga toxin-producing Escherichia coli (E. coli). A key message that I heard from several speakers was that we know enough today to develop policies that can enable action in addressing the most pressing foodborne hazards.

Ground BeefCentral to the development of smarter food policies is incorporating our understanding the ecology of foodborne microbes. For example, understanding the ecology of toxin-producing E. coli strains can improve our ability to detect the right types of E. coli in tainted foods. In another example, nontherapeutic use of antibiotics in food animal production creates a persistent collection of antibiotic-resistant bacterial genes or a ‘resistome’ on farms that is difficult to dismantle. Antibiotic-resistance genes transferred to pathogenic bacteria creates a health hazards for animal workers, slaughterhouse workers, farm neighbors, and to consumers who handle or prepare raw meat in their kitchens.

Antibiotic-resistant pathogens

The Pew/CSPI conference focused on antibiotics in food animals because in 2009 nearly 80% by weight of all antimicrobials were sold for use in food animal, and the remaining 20% by weight were used in human medicine, as reported last year by Ralph Loglici on the Livable Future Blog.

Resistance is an inevitable result of using antibiotics on food animals or humans. In the words of Quijing Zhang of Iowa State University, “[it is] always going to happen.” Once gut bacteria become resistant to antibiotics, they can trade the blueprints for resistance to other beneficial bacteria or with pathogenic bacteria in a giant microbial swap meet called ‘the resistome.’

 The microbial world’s resistome and our own human-centered biome collide more often than we think—just talk to a health care provider about hospital-acquired antibiotic resistant infections or read the latest 2008 report on the quality of retail meats from the U.S. National Antimicrobial Resistance Monitoring System.

 When humans take antibiotics or animals are given antibiotics, these are individual decisions—and as Dr. Stuart Levy of Tufts University pointed out, “[these individual decisions have] societal effects when antibiotics are mismanaged, such that every dose of antibiotics has a consequence.” Levy underscores the severity of current practices, saying, “the fact that we are still practicing [the use of antibiotics in animal production] is an embarrassment and a mistake.”

How does one begin to address the pressing public health crisis of antibiotic resistance? Hagan cited surveillance as essential. Beginning in 1996 the National Antimicrobial Resistance Monitoring System (or NARMS) has, as Hagan said, “reinforced, with data, our belief that pathways to antimicrobial resistance—both human and animal—must be managed.” Hagan provided no policy solutions in her talk but reassured the audience that “regulators and industry are thinking about this challenge.”

 Several speakers proposed physical and methodological management changes for animal production:

  • Dr. Scott Brown of Pfizer Animal Health provided a list of potential management directions, one of which was that the FDA should reduce over-the-counter sales of antibiotics and ask veterinarians to write prescriptions for antibiotics given to food animals, similar to doctor-patient relationships for prescriptions in human medicine. Brown’s rationale was that antibiotics require significant investments in research and development to create and should not be squandered.
  • Dr. Hendrik Wegener, Director of the Nation Food Institute in Denmark, suggested the US remove economic incentives for veterinarians to over-prescribe antibiotics, a strategy that was useful in his country.
  • Dr. H. Morgan Scott of Kansas State University advocated for changing the farm environment as the only long-lasting way to slow resistance on farms. His rationale was that the cumulative, historic effects of using antibiotics on conventional industrial food animal farms have created a community of resistance genes (i.e. a resistome) within the farm environment. Applying an ecological perspective, explains Scott, “the environment is a reflection of the animal, and the animal is a reflection of the environment.”

 In addition to speakers management changes, it is worth reiterating that the root cause of antibiotic-resistance in food animal production is the use of antibiotics. Future policies should eliminate non-therapeutic antimicrobials in food animal production to slow antimicrobial resistance on farms.

Shiga toxin-producing E. coli

The second half of the Pew/CSPI conference focused on toxin-producing E. coli. In the microbiome, E. coli is usually a garden variety or commensal organisms living in our guts and other environmental niches. A few intestinal E. coli species can produce a toxin that causes abdominal pain, vomiting, and diarrhea, and scientists had often wondered how did these E. coli become so virulent?

Most now believe that in the not-too-distant past, a virus essentially stole the blueprints for making shiga toxin from a Shigella bacterium, and delivered the blueprints to an E. coli bacterium. E. coli spread these toxin blueprints to its progeny through replication—bacteria divide by doubling—and have since colonized the guts of beef cattle and other animals. A well-known shiga toxin-producing E. coli is E. coli O157:H7, responsible for disease outbreaks and deaths caused by consuming undercooked ground beef, vegetables contaminated with feces, and drinking contaminated water.

 However, as conference presenters Drs. Patricia Griffi and Peter Gerner-Smidt of the Centers for Disease Control and Prevention pointed out, E. coli O157:H7 is not to blame for all E. coli foodborne outbreaks. Through understanding the ecology and phylogeny of toxin-producing E. coli, Griffin and Gerner-Smidt explained the evidence base for regulating other toxin-producing E. coli species.

Why is shiga toxin-producing E. coli is a widespread problem? In part because of the farm environment— the US cattle industry raises more than 30 million head of beef cattle a year—a large fraction of those spend time on feedlots—providing an environment for shiga toxin-producing E. coli to compete with other cattle gut flora. Slaughterhouses are also messy environments, where pathogenic E. coli present in one animal can contaminate whole batches of ground beef—causing both large and small recalls. Better sanitation practices in home kitchens will also help prevent cross-contamination and transfer of foodborne pathogens.

 The Pew/CSPI conference was latest great example of how scientists, regulators, and industry need to continue to share information about the pubic health implications in our food system.

Information gaps can be addressed with better monitoring and tracking of foodborne diseases in humans, food animals and slaughterhouses, more information collected about antibiotic usage on farms, and enhancing consumer awareness of farming through programs like USDA’s “Know your farmer know your food.” In the short term, many pragmatic solutions to foodborne hazards could be reached where public health and business interests overlap.

Overall, eliminating all foodborne hazards may not be possible. However an effective harm reduction strategy could be informed by much of what Fred Kirschenmann talks about, including the value of “treating food less like a commodity and more like a relationship.”

 – Dave Love







Leave a Comment

Your email address will not be published. Required fields are marked *