Resistant Escherichia coli--we are what we eat.

Received 30 March 2009; accepted 30 March 2009; electronically published 9 June 2009. Reprints or correspondence: Prof. Peter Collignon, Infectious Diseases Unit and Microbiology Department, The Canberra Hospital, PO Box 11, Woden, ACT 2606, Australia (peter.collignon@act.gov.au). Clinical Infectious Diseases 2009; 49:202–4 2009 by the Infectious Diseases Society of America. All rights reserved. 1058-4838/2009/4902-0006$15.00 DOI: 10.1086/599831 Escherichia coli is a frequent cause of lifethreatening bloodstream infections [1] and other common infections, such as urinary tract infections. Antibiotic resistance rates in E. coli are rapidly rising, especially with regard to fluoroquinolones and thirdand fourth-generation cephalosporins. Surprisingly, most of these multidrug-resistant strains are acquired in the community rather than in healthcare settings [2, 3]. Drug-resistant E. coli are readily acquired via the diet (food and water), and there is a major turnover of drug-resistant E. coli each day [4]. When people eat sterile food, there is a rapid and substantial fall in the numbers of drug-resistant E. coli these people carry [4]. What remains unclear is where the drug-resistant E. coli in our food are coming from. Are they mainly human strains that contaminate our food (and water), or are these strains mainly derived from food animals? The study by Johnson et al [5] in this issue helps to answer this important question. They analyzed 287 E. coli isolates recovered from meats for a large number of virulence factors and resistance markers. They showed that drug-resistant isolates had characteristics very similar to those of susceptible isolates recovered from the same types of meat but quite different from those of isolates found in other types of meat. Put another way, the drug-resistant isolates found on retail poultry products are very similar to susceptible isolates found on retail poultry products, compared with drug-resistant or susceptible isolates of E. coli recovered from pork or beef. Thus, it is very likely that most drugresistant isolates found on poultry meat, for example, are the result of antibiotic use in poultry (rather than the result of the introduction of strains from people or other animals into poultry flocks or the cross-contamination of poultry meat after slaughter). Although this fact may seem obvious, it has not been readily accepted by many people associated with the agriculture and pharmaceutical sectors. There are limitations in this study. The authors only looked at resistance to a few antibiotics and relatively small numbers of isolates (especially for some food). Grocery stores in only 4 United States geographical sites were sampled. However, it is hard to see how an expansion of their study to many more sites and an increased sample size would have altered their highly convincing and statistically significant findings. The applicability of these findings to the E. coli found on food from regions or countries where human fecal material may frequently contaminate food or water will, however, need further study. Some people argue that antibiotic-resistant strains that develop in food animals are largely irrelevant to human health because E. coli strains are relatively speciesspecific and so will not cause disease in people. This current study [5] shows that argument is flawed. A large proportion of isolates in these meats possessed virulence factors associated with causing disease in people. Even if some E. coli animal strains are relatively species-specific, the antibiotic resistance genes carried in animal strains are likely to be much less hostspecific and thus transferrable to bacteria carried more frequently by people. We carry large numbers of E. coli in the bowel (more than 1 10 organisms per gram of feces) [4]. Johnson et al [6] have shown elsewhere that the majority of drug-resistant E. coli carried by people are likely derived from food animals (especially poultry). Indeed, susceptible strains carried by people are very different in characteristics to the drug-resistant E. coli strains they carry. Indeed, the latter are much more similar to susceptible poultry strains than to susceptible human strains. What does this mean? It is very likely that a large proportion of the drug-resistant strains of E. coli carried by people are acquired via food and especially food animals. We know that highly drug-resistant strains of E. coli (resistant to fluoroquinolones, to extended-spectrum b-lactams, etc) are spreading into the community