First US Case of E coli Resistant to Last-Resort Antibiotic

May 26, 2016

Researchers have spotted the first known instance of bacteria impervious to the last-resort antibiotic colistin in the United States, exacerbating fears of superbugs that can turn an ordinary infection deadly.

The case involves a 49-year-old woman treated at a clinic in April for a urinary tract infection. A urine culture revealed a strain of Escherichia coli that was later found to be resistant to colistin. The findings were published online today in Antimicrobial Agents and Chemotherapy.

In a speech at the National Press Club today, the head of the Centers for Disease Control and Prevention (CDC) said the study is a call to develop new antibiotics and use them wisely.

"The medicine cabinet is empty for some patients," said CDC Director Thomas Frieden, MD, MPH. "It is the end of the road for antibiotics unless we act urgently."

What is even more alarming about the case of the Pennsylvania woman is that the E coli became resistant to colistin not through mutation, but by acquiring a snippet of DNA called a plasmid that carries the resistance-conferring gene. Such plasmids easily spread from bacterium to bacterium.

"The recent discovery of a plasmid-borne colistin-resistance gene, mcr-1, heralds the emergence of truly pan-drug resistant bacteria," write the authors, all associated with Walter Reed National Military Medical Center in Maryland.

Although the authors say this is the first report of mcr-1 in the United States, the colistin-resistance gene has surfaced in bacteria in other countries, notably China.

The Pennsylvania woman had not reported any travel during the previous 5 months. The study does not describe her current condition.

"Continued surveillance to determine the true frequency for this gene in the USA is critical," the authors write.

In his speech today, Dr Frieden described colistin as the only antibiotic left "for what I call the nightmare bacteria, carbapenem-resistant enterobacteriaceae (CRE)."

It turns out that the Pennsylvania woman''s infection was not resistant to carbapenem antibiotics, another CDC official told Medscape Medical News. However, Christopher Braden, MD, deputy director of the agency's National Center for Emerging and Zoonotic Infectious Diseases, warned that the plasmid-borne colistin-resistance gene could transfer to CRE or any other superbug, making them deadlier.

The CDC and the US Department of Defense are working with the Pennsylvania Department of Health (DPH) to investigate the case of colistin-resistant E coli, according to a DPH news release. The DPH said that state law prevents it from disclosing specific details about the inquiry or the patient.

Antimicrob Agents Chemother. Published online May 26, 2016. Full text

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