One Health/Public Health community expresses alarm after first U.S. report of colistin- and carbapenem-resistance genes in common strain of E. coli bacteria.

By Stephanie Ostrowski

A common strain (ST405) of E. coli containing genes for resistance to both colistin and carbapenem antibiotics has been isolated from a hospitalized patient in the United States, the University of Minnesota’s Center for Infectious Disease Research and Policy (CIDRAP)  announced. The patient, a 76-year old immigrant from India, was being treated for recurrent urinary tract infections and had lived in the U.S. continuously for one year prior to his hospitalization.

Although the ST405 isolate was resistant to colistin as well as all but one of the beta-lactam antibiotics, this patient’s bacterial infection was susceptible to several other unrelated antibiotics (amikacin, gentamicin, nitrofurantoin, tigecycline, and trimethoprim-sulfamethoxazole).

Colistin is a rarely-used “antibiotic of last resort,” reserved to treat life-threatening drug-resistant infections in humans.

Responsible stewardship of antibiotics has become a watchword for both the veterinary and medical professions over the past two decades. This change has led to major shifts in professional consensus guidance, policy, and practice for the United States and European Union nations, with corresponding emphasis on national and international programs for monitoring through laboratory surveillance and regulatory oversight.

As a result, physicians no longer routinely prescribe antibiotics as part of treatment for seasonal respiratory viruses. And beginning in January 2017, routine administration of subtherapeutic levels of antimicrobials in the feed or water of food-producing animals in the U.S. is prohibited as “injudicious use” of antibiotics. A Veterinary Feed Directive (VFD) prescription from a licensed U.S. veterinarian will be required whenever therapeutic administration of antibiotics via feed or water is deemed necessary for an animal population.

Much of the globe has yet to adopt these measures, however. In many countries average citizens can directly purchase any type of medication over the counter to treat themselves and their animals. Van Boeckel et al1 (2015) have attempted to quantify antibiotic consumption in livestock for 228 nations around the world, and their analysis is disturbing.

The authors “….conservatively estimate the total consumption in 2010 at 63,151 tons…(and) project that antimicrobial consumption will rise by 67 percent by 2030, and nearly double in Brazil, Russia, India, China, and South Africa….Up to a third of the increase in consumption in livestock between 2010 and 2030 is imputable to shifting production practices in middle-income countries where extensive farming systems will be re-placed by large-scale intensive farming operations that routinely use antimicrobials in subtherapeutic doses…. These practices contribute to the spread of drug-resistant pathogens in both livestock and humans, posing a significant public health threat.”

What are the important take-away points for U.S. clinicians, public health officials, and the food and agricultural sectors with regard to this news?

  • This is the first U.S. report of the clinical isolation of an E. coli strain resistant to both carbapenem and colistin types of antibiotics.
  • Colistin is a rarely-used “antibiotic of last resort” in human medicine. Because it is not routinely used, the expectation has been that it would be possible to reserve it to treat life-threatening drug-resistant infections in humans and minimize the likelihood that antimicrobial resistance would develop.
  • However, less than one year ago—in November 2015—Chinese researchers announced they had identified a colistin-resistance gene (mcr-1) in multiple E. coli isolates obtained in China from pigs, pork products, and humans.
  • Since then, the U.S. and at least 30 other countries have reported finding enteric bacteria containing the mcr-1 resistance gene and have recognized that it can readily be shared with other types of bacteria through plasmid transfer (a plasmid is a mobile piece of DNA that can easily be shared with other types of bacteria).
  • The ST405 strain of E. coli is further described by ProMED–mail rapporteur Mary Marshall as an E. coli sequence type that is “frequently associated with community-onset urinary tract infections. Dissemination of mcr-1 within this global lineage may therefore contribute to further spread of colistin resistance” (ProMED-mail is a program of the International Society for Infectious Diseases).
  1. Van Boeckel TP, Brower C, Gilbert M, Grenfell BT, Levin SA, Timothy P. Robinson, Teillant A, Laxminarayan R. Global trends in antimicrobial use in food animals. (2015) PNAS Early Edition, p. 1-6. pnas.org/cgi/doi/10.1073/pnas.1503141112

Dr. Stephanie Ostrowski, DVM, MPVM, DACVPM, is an associate professor of public health in the Auburn University College of Veterinary Medicine. She is a Distinguished Fellow of the National Academies of Practice as well as a retired U.S. Public Health Service Officer, formerly at the Centers for Disease Control (CDC).

Photo credit:  Janice Haney Carr, Centers for Disease Control and Prevention