Two new studies in Emerging Infectious Diseases provide more evidence of the spread of MCR-1, the gene that confers resistance to the last-resort antibiotic colistin, in both animals and humans, including an isolate that was resistant to multiple antibiotics.
In the first study, an international group of researchers reported that, out of 150 strains of Escherichia coli cultured from the fecal samples of European cattle from 2004 through 2010, 45 were classified as multidrug-resistant. Three of those multidrug-resistant strains showed elevated levels of resistance to colistin. Further analysis identified one isolate—an E coli 29957 strain—as MCR-1 positive.
In addition, that isolate was found to be resistant to all other classes of antibiotics tested against it, including beta-lactams, fluoroquinolone compounds, and florfenicol. The authors of the study said this finding is particularly concerning.
The MCR-1 gene was first reported late last year by researchers who found it in a strain of E coli bacteria identified in pigs, raw pork meat, and a handful of hospitalized patients in China. Since then it has been detected in bacteria from animals, humans, food, and the environment in at least 30 countries. A recent study out of Germany detected the MCR-1 gene in 402 out of 505 colistin-resistant E coli isolates.
The gene has raised alarms among public health officials because colistin is a powerful antibiotic that is used when bacterial infections—such as gram-negative E coli—won't respond to other antibiotics. And because MCR-1 is located on mobile pieces of DNA known as plasmids, it can jump to different strains of bacteria and therefore has the ability to spread rapidly among both humans and animals.
Of greatest concern is the potential for MCR-1 to latch onto multidrug-resistant bacteria, which could lead to infections that are nearly impossible to treat.
The researchers said that the MCR-1 gene identified in the bovine E coli isolate was 100% similar at the nucleotide level to the gene detected in China in November 2015.
MCR-1 identified in a patient
While the spread of colistin resistance and the MCR-1 gene has been well documented in animals, fewer human cases of plasmid-mediated colistin resistance have been reported. But the spread of the gene into the population is being carefully monitored.
In a letter to the editor, a team of Canadian researchers reported on a case involving a 61-year-old man with drug-resistant E coli. Further analysis found that the E coli strain was resistant to colistin, and genome sequencing confirmed the presence of the MCR-1 gene.
According to the report, the patient developed the infection at a Vancouver hospital after undergoing a prostate procedure to treat obstructive urinary tract symptoms. The patient had also traveled to China in November 2015 and had been hospitalized for urinary retention while in the country. The researchers said this history suggested the E coli was likely acquired in the Chinese hospital, as the patient denied having any contact with farm animals, live-poultry markets, and undercooked food.
The patient was treated with amoxicillin/clavulanate and was discharged from the hospital after 5 days. Other patients who shared a hospital room with the man were not screened.
The researchers said that while retrospective screening has identified MCR-1 isolates in Canada, this is the first case of a patient being prospectively identified with MCR-1–harboring E coli. They urged routine colistin testing for Enterobacteriaceae to get a better estimate on the real prevalence of MCR-1
See also:
Aug 1 Emerg Infect Dis dispatch
Aug 1 Emerg Infect Dis letter
Jul 26 CIDRAP News story "German researchers identify 402 MCR-1 isolates"
