FROM ANTIMICROBIAL AGENTS AND CHEMOTHERAPY
In what is believed to be the first case of its kind in the United States, researchers identified a female patient with colistin-resistant Escherichia coli. The patient harbored mcr-1, a gene resistant to colistin, an antibiotic used as a last resort for infections that are resistant to carbapenems.
The finding comes at a time when a search for colistin-resistant bacteria by officials from the U.S. Department of Agriculture and the U.S. Department of Health and Human Services revealed colistin-resistant E. coli in a single sample from a pig intestine. Combined, “these discoveries are of concern because colistin is used as a last-resort drug to treat patients with multidrug resistant infections,” according to a communication from the HHS dated May 26. “Finding colistin-resistant bacteria in the United States is important, as it was only last November that scientists in China first reported that the mcr-1 gene in bacteria confers colistin resistance.”
Researchers led by Patrick McGann, Ph.D., who reported the human case in an article published online May 26 in Antimicrobial Agents and Chemotherapy, wrote that the recent discovery of a plasmid-borne colistin resistance gene, mcr-1, “heralds the emergence of truly pan-drug resistant bacteria. The gene has been found primarily in Escherichia coli, but has also been identified in other members of the Enterobacteriaceae from human, animal, food and environmental samples on every continent” (Antimicrob Agents Chemother. 2016 May 26. doi: 10.1128/AAC.01103-16).
As a result of this threat, in May, Dr. McGann, of the Department of Defense’s Multidrug-resistant Organism Repository and Surveillance Network at Walter Reed Army Institute of Research, Silver Spring, Md., and his associates began analyzing all extended-spectrum beta-lactamase (ESBL)–producing E. coli clinical isolates submitted to Walter Reed National Military Medical Center for analysis for resistance to colistin by E-test.
The case of interest was the presence of mcr-1 in an E. coli isolate cultured from a 49-year-old woman who presented to a military clinic in Pennsylvania with symptoms suggestive of a urinary tract infection, and who reported no travel history within the prior 5 months. Susceptibility testing at Walter Reed indicated an ESBL phenotype.
“The isolate was included in the first 6 ESBL-producing E. coli selected for colistin susceptibility testing, and it was the only isolate to have a MIC of colistin of 4 mcg/mL [all others had MICs of 0.25 mcg/mL or less]. Colistin MIC was confirmed by microbroth dilution and mcr-1 detected by real-time PCR.”
Since mcr-1 testing at Walter Reed has been underway for a short time, “it remains unclear what the true prevalence of mcr-1 is in the population,” the researchers noted. “The association between mcr-1 and IncF plasmids is concerning as these plasmids are vehicles for the dissemination of antibiotic resistance and virulence genes against Enterobacteriaceae. Continued surveillance to determine the true frequency for this gene in the USA is critical.”
The researchers reported having no financial disclosures.
