Understanding foodborne microbial hazards for smarter food policies

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.”

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AVMA leadership missing key facts on antibiotics in food animals

Dr. Ron DeHaven, CEO and Executive VP of the American Veterinary Medical Association (AVMA)*, spoke last week to the pork industry in Kansas City, MO. DeHaven opposes legislation to ban the use of non-therapeutic (growth promoting) antibiotics and antibiotics with human uses from food animal production. DeHaven used this opportunity to spread misinformation about the reality and consequences of non-therapeutic antibiotic use and food safety.


Early MRSA infections. http://www.jiujitsuforums.com/wiki/File:Mrsa7.jpg

DeHaven seems to understand the biological basis for antibiotic resistance, by saying “antimicrobial resistance is caused by widespread use of antimicrobials in food production systems, and hence the more we expose microorganisms to antibiotics the more likely they are to develop that resistance.” The problem arises in his dismissal of the impacts of using antibiotics in food animals—a practice that experts recognize as a public health threat (Silbergeld et al., 2008).

In his talk DeHaven said, “there really is no scientific evidence to confirm just how, if, and to what extent that exposure represents a risk to human health… there has been really no case of human infection with resistant bacteria that has been proven to be caused by the use of antimicrobials in food animals.” This statement is disingenuous and does not acknowledge published findings to the contrary (Voss et al., 2005; Huijsdens et al., 2006) demonstrating MRSA (Methicillin-resistant Staphylococcus aureus) transmission from pigs to a pig farmer, and between pig farmers and their family.

Reported cases of disease are only the tip of the iceberg, therefore we expect that many more cases of community associated (i.e. non-hospital) antibiotic resistant bacterial diseases have originated from factory farms. A recent study in the Journal Emerging Infectious Diseases shows that community associated diseases are increasing at an alarming rate— over 33% increase annually for MRSA in the US from 1999 to 2006 (Klein et al., 2009). While all cases of MRSA may not originate on factory farms, we can’t rule out factory farms and as one source of MRSA (Nunan and Young 2007).

In addition to MRSA, resistant E. coli have been detected in cattle and pigs given antimicrobial drugs (Alexander et al., 2008; Rosengren et al., 2008). When antibiotics are given to food animals, as much as 75% of those drugs are excreted in waste, which contributes to the environmental burden of antibiotic residues and the development of resistant bacteria in the environment (Chee-Sanford et al., 2009). Regulations to reduce or ban antibiotics used in food animals appears to be one clear way we can reduce one source of resistant bacteria.

At the end of his talk, DeHaven takes a stance in support of greater oversight of drug delivery to animals by veterinarians. This would be laudable, except for a giant loop-hole he introduces when saying “veterinary involvement needs to be consistent or proportionate with the risk of those antibiotics.” This insinuates that continuing the practice of selling antibiotics over-the-counter (OTC) in feed to farmers, with no veterinary oversight, is acceptable. The AVMA is investigating other ways of relaxing food animal veterinary oversight, with increased involvement of veterinary technician and electronics prescriptions of antibiotics. With region-specific shortage of mixed animal veterinarians in the US, can you blame the AVMA for feeling squeamish about its options for taking care of the burgeoning numbers of food animals? Read More >