Washington: Bacteria carrying the MCR-1 "superbug" gene was found in a second US patient, researchers said on Monday. The gene was detected in an isolate of Escherichia coli that was originally recovered in 2015 from a patient in New York, according to the research published in Antimicrobial Agents and Chemotherapy, a journal of the American Society for Microbiology. Previously, Escherichia coli bacteria carrying the MCR-1 gene was identified in a urine sample from a Pennsylvania woman in May who had no recent travel records outside of the US, Xinhua news agency reported. The MCR-1 gene makes bacteria resistant to the antibiotic colistin, which is used as a last-resort drug to treat patients with multi-drug-resistant infections, including carbapenem-resistant Enterobacteriaceae (CRE). US health experts said the discoveries would be concerning because the MCR-1 gene exists on a plasmid, a small piece of DNA that is capable of jumping between different bacterial species, spreading any resistance genes it carries. In the current study, the researchers, who coordinated the worldwide SENTRY Antimicrobial Surveillance Programme, first tested 13,526 Escherichia coli and 7,480 Klebsiella pneumoniae strains that had been collected from hospitals in the Asia-Pacific region, Latin America, Europe, and North America in 2015. They found that 390, or 1.9 per cent, were resistant to colistin, and that 19 of these isolates tested positive for MCR-1. The MCR-1 gene was first isolated from food animals and humans in China in late 2015. Following that, scientists across the globe began searching for other bacteria containing the MCR-1 gene, and the bacteria have since been discovered in Europe and Canada.