Rutgers & Columbia Researchers Discover New Strain of Multi-drug Resistant E. coli

Around the world, researchers studying antibiotic-resistant bacteria are working to understand these pathogens as quickly as the germs are adapting. In that effort, a team of scientists recently discovered a new strain of Escherichia coli (E. coli) believed to be the first in the United States with resistance to two kinds of antibiotics considered to be last resort weapons to prevent dangerous infections.

In their research paper, published in The American Society for Microbiology’s journal, mBio, the group of Rutgers University and Columbia University researchers detail the case of an E. coli strain found in samples taken from a 76-year-old male hospital patient in 2014. The authors explain prior findings on a plasmid-borne colistin resistance gene called mcr-1, which scientists had previously discovered in samples in China and other parts of the world, but which had never appeared in the United States. Of concern to researchers has been the potential discovery of mcr-1 appearing in US samples, as well as the spread of the gene into Enterobacteriaceae with the carbapenem-resistance gene blaNDM-5. In this case, say the authors, they’ve discovered the occurrence of both in a strain of E. coli approaching pan-resistance.

In an exclusive interview with Contagion, study author Barry Kreiswirth, PhD, of the Public Health Research Institute Center at Rutgers University, discussed the significance of these new findings.

Urine cultures obtained from the patient’s sample showed the presence of multiple bacteria such as Pseudomonas aeruginosa, Citrobacter koseri, Enterococcus faecium, P. aeruginosa, Klebsiella pneumoniae, Enterococcus spp., methicillin-resistant Staphylococcus aureus, and E. coli. After conducting drug susceptibility tests on the isolated strains, the researchers discovered that the E. coli isolate present in the sample exhibited resistance to colistin as well as all beta lactams, including carbapenems.

With the rise of carbapenem-resistant bacteria, colistin has increasingly become an antibiotic considered the last line of defense for hard-to-treat infections. According to the Centers for Disease Control and Prevention, at least 2 million people in the United States become infected with antibiotic-resistant bacteria and 23,000 die as a result each year. Bacteria can form antibiotic resistance—and dangerous infections can occur in people–through exposure to antimicrobial agents. The drugs used to fight the bacteria may destroy certain germs, but some microbes are naturally stronger and more resilient and can resist the effects of the drugs. Once the antibiotics kill off much of the pathogenic bacteria, as well as the beneficial microflora present in our bodies, those drug-resistant bacteria unharmed by the treatment can then grow and take over. That resistance can then spread to other bacteria.

In this case detailed in the new study, while the mcr-1- and blaNDM-5-harboring E. coli was resistant to both carbapenem and colistin, the isolate did show susceptibility to the antibiotics aztreonam, amikacin, gentamicin, nitrofurantoin, tigecycline, and trimethoprim-sulfamethoxazole.

“The mcr-1 gene that we found in our strain has also been found in other strains throughout the United States,” said Dr. Kreiswirth during the interview with Contagion, explaining that isolates containing mcr-1 have been found in pig and bovine samples. He noted that it wasn’t unforeseen to find the colistin-resistance gene in animal reservoirs as the antibiotic has been used in cattle and pig feedlots. “The surprise wasn’t that we found it in a human; the surprise was that we found it in association with a second resistance gene, which was the carbapenem-resistance gene. That’s the new finding.”

As Dr. Kreiswirth and his team continue to study mcr-1 in the United States, he pointed out a recent study on the finding of a second colistin-resistance gene dubbed mcr-2, and the possibility that other still-unidentified resistance genes are out there.

More of the interview with Dr. Kreiswirth is available here:

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