Antibiotic Resistance from Animal Agriculture: Foodborne Illness and Medical Care
Resistant Pathogens in the Food Supply
Salmonellae, Campylobacter, E. coli, and Yersinia bacteria thrive in the intestinal tracts of animals. Although vegetables such as spinach, tomatoes, or sprouts can become tainted with enteric bacteria, these pathogens originate in the intestines of animals.
Manure from infected animals can carry disease-causing bacteria into fields and waterways. A recent study of the bacteria in waterways found in a U.S. agricultural region showed that 98 percent of fecal coliform isolates sampled were resistant to at least one antibiotic (ampicillin). The concentration of multidrug resistant fecal coliform isolates downstream from concentrated animal feeding operations (CAFOs) and fields fertilized with manure from CAFOs was 2.5 times higher than at sites further from animal-waste runoff.6
Methicillin-resistant Staphylococcus aureus (MRSA), though not a fecal bacteria, is also prevalent among farmed animals. An Iowa study found that 49 percent of pigs and 45 percent of pig-farm workers tested positive for MRSA.7 Similar patterns were also found in the Netherlands,8 Denmark,9 and Canada.10
Animal products are frequently associated with antimicrobial-resistant foodborne disease outbreaks. However, the Centers for Disease Control and Prevention (CDC) does not require reporting of these occurrences. Because of this, there is limited information available on these outbreaks.
In 2011, the Center for Science in the Public Interest published an independent survey of foodborne illness due to antimicrobial-resistant bacteria. The number of outbreaks has increased each year since 1970, and 40 percent of outbreaks occurred between 2000 and 2010. The contaminated products were most frequently dairy products (12 outbreaks, 34 percent) followed by ground beef (nine outbreaks, 26 percent); poultry, pork, seafood, and eggs (seven outbreaks, 20 percent); unknown (four outbreaks, 11 percent); produce (2 outbreaks, 6 percent); and multi-ingredient (one outbreak, 3 percent). The resistant bacteria responsible were mostly strains of salmonellae (28 of 35 outbreaks) but also included strains of E. coli, Campylobacter jejuni, and S. aureus. More than half of the strains are resistant to at least five antibiotics. These outbreaks were responsible for 19,897 infections, which lead to 3,061 hospitalizations and 26 deaths.11