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

Marcia Frellick

July 11, 2016

Bacteria resistant to colistin, an antibiotic of last resort, have been found in a second patient in the United States, according to a study published today. The finding raises concerns about the possible emergence of bacteria resistant to all existing antibiotics.

As previously reported by Medscape Medical News, researchers reported the first case of colistin-resistant bacteria in the US in May. That patient, from Pennsylvania, carried a colistin-resistant strain of Escherichia coli(E coli) bacteria.

The newly identified case is from a patient who had surgery in a New York hospital in 2015 and was identified as part of the most comprehensive surveillance project for the colistin-resistance gene, mcr-1, to date.

Mariana Castanheira, PhD, director for molecular and microbiology, at JMI Laboratories in North Liberty, Iowa, and colleagues published their findings online in Antimicrobial Agents and Chemotherapy.

In the current study, which is part of the worldwide SENTRY Antimicrobial Surveillance Program,, Dr Castanheira and colleagues tested 13,526 E coli and 7,480 Klebsiella pneumoniae clinical strains collected in 2015 from hospitals in the Asia-Pacific region, Europe, Latin America, and North America.

Of those, 390, or 1.9%, E coli isolates were resistant to colistin, and 19 of these isolates tested positive for mcr-1. None of the K pneumoniae isolates were resistant to the drug.

The 19 resistant isolates originated in 10 countries; one came from the US. The other countries with mcr-1-resistant isolates include Belgium (1 isolate), Brazil (1), Germany (5), Hong Kong (1), Italy (4), Malaysia (1), Poland (1), Russia (1), and Spain (3).

All of the colistin-resistant isolates reported in the current study, including the one from New York, were susceptible to other commonly used antibiotics, including recently approved agents.

However, the researchers are concerned that the bacteria could transfer genes to other bacteria already resistant to all antibiotics.

"The fact that the gene has been detected in food livestock and raw meat is also concerning," Dr Castanheira said in a press release.

The authors note that it is not yet clear if the mcr-1 gene from the New York patient is encoded in the bacterial chromosome or in a plasmid. If it is encoded in a plasmid, that is cause for extra concern, as bacteria can easily pass plasmids to other strains and thus transfer the resistance gene.

The mcr-1 gene has been found in bacteria in other countries, notably in China last fall, as previously reported by Medscape Medical News. That was where mcr-1 was first isolated from food animals and humans.

In the case of the Pennsylvania woman, E coli became resistant to colistin not through mutation but by acquiring a plasmid carrying the resistance gene.

"The prospect of a mobile gene encoding resistance to colistin spreading among isolates resistant to most antimicrobial agents clinically available is threatening for the therapy of serious infection caused by isolates," the investigators conclude.

JMI Laboratories, Inc has also received research and educational grants in 2014-2015 from Achaogen, Actavis, Actelion, Allergan, American Proficiency Institute (API), AmpliPhi, Anacor, Astellas, AstraZeneca, Basilea, Bayer, BD, Cardeas, Cellceutix, CEM-102 Pharmaceuticals, Cempra, Cerexa, Cidara, CorMedix,Cubist Pharmaceuticals, Debiopharm, Dipexium, Dong Wha, Durata, Enteris, Exela, Forest Research Institute, Furiex, Genentech, GSK, Helperby, ICPD, Janssen, Lannett, Longitude, Medpace, Meiji Seika Kaisha, Melinta, Merck, Motif, Nabriva, Novartis, Paratek, Pfizer, Pocared, PTC Therapeutics, Rempex, Roche, Salvat, Scynexis, Seachaid, Shionogi, Tetraphase, The Medicines Co, Theravance, Thermo Fisher, VenatoRx, Vertex, Wockhardt, Zavante, and other corporations. Some JMI employees are advisers/consultants for Allergan, Astellas, Cubist, Pfizer, Cempra and Theravance.

AAC. Published online July 11, 2016.


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