August 31, 2016
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E. coli strain resistant to colistin and carbapenems detected in New Jersey

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For the first time, resistance to both colistin and carbapenems has been detected in a patient in the United States.

Researchers in New Jersey who have been analyzing clinical isolates of gram-negative bacteria from a tertiary-care hospital discovered an Escherichia coli isolate that carried both the colistin-resistant mcr-1 and carbapenem-resistant blaNDM-5 genes.

The E. coli strain was identified from a urine sample collected in August 2014 — the earliest date so far that the mcr-1 gene has been detected in the U.S.

There was good and bad news in the discovery, according to Barry N. Kreiswirth, PhD, director of the Public Health Research Institute (PHRI) Tuberculosis Center at Rutgers University, who co-authored a report about the finding in mBio.

“The good news is that this did not cause a major outbreak of drug-resistant infection,” he said in a news release. “The bad news is that since this occurred two years ago, there are clearly other strains out there we haven’t detected yet. Both the carbapenem resistance and the colistin resistance genes are on separate plasmids, which means in principle they could spread to other bacteria.”

The discovery last year of the mcr-1 gene in Chinese livestock and hospital patients heightened fears over drug resistance. The gene was not detected in the U.S. until this year when it was found in E. coli isolates taken from patients in Pennsylvania in 2016 and New York in 2015.

But resistance to both colistin, a last-resort antibiotic, and broad-spectrum carbapenems had not been reported in the U.S. until now.

As colistin is increasingly used to treat infections that are resistant to multiple classes of antibiotics — in particular carbapenem-resistant Enterobacteriaceae — such strains of bacteria approach so-called pan-resistance, Kreiswirth and colleagues wrote.

They discovered the multidrug-resistant E. coli strain in the urine sample of a man, aged 76 years, who had emigrated from India but had lived in the U.S. continuously for 1 year with no recent history of travel. The man had developed recurrent urinary tract infections following radiation therapy for prostate cancer and had recently undergone a cystoscopy. During the procedure, his bladder was perforated and he required a bilateral nephrostomy tube, which later provided a urine culture that contained the E. coli strain.

The isolate was not only resistant to colistin and all beta-lactams except aztreonam, but also aminoglycosides, chloramphenicol, fluoroquinolones, rifampin, sulfonamides and tetracycline, Kreiswirth and colleagues reported. It remained susceptible to amikacin, gentamicin, nitrofurantoin, tigecycline, and trimethoprim-sulfamethoxazole.

They named the strain MCR1_NJ.

José R. Mediavilla, MBS, MPH, research teaching specialist at PHRI, said it was concerning that the mcr-1 gene was showing up in E. coli, the most common cause of urinary tract infections.

“These strains are probably already in the community and could spread further, essentially building toward a situation where you’re going to have difficult if not impossible to treat urinary tract infections,” he said in the release. “Active surveillance efforts involving all colistin- and carbapenem-resistant organisms are imperative to determine mcr-1 prevalence and prevent future dissemination.” – by Gerard Gallagher

Disclosure: Kreiswirth reports holding two patents related to this work.