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If you’ve been following the news about antibiotic resistant bacteria, you may have heard about a particularly alarming plasmid: MCR-1. A plasmid is a circle of DNA that is relatively small and mobile – an easy way for genetic information to spread between bacteria. MCR-1 raises concern because it provides bacteria resistance against the last-resort antibiotic colistin. The CDC reports MCR-1 was found in both patients and livestock in the United States this summer.
David Weiss, director of Emory’s Antibiotic Resistance Center, and colleagues have a short letter in The Lancet Infectious Diseases showing that MCR-1 also confers resistance to an antimicrobial enzyme produced by our bodies called lysozyme. MCR-1-containing strains were 5 to 20 times less susceptible to lysozyme, they report.
This suggests that the pressure of fighting the host immune system may select for MCR-1 to stick around, even in the absence of colistin use, the authors say.
While the findings are straightforward in bacterial culture, Weiss cautions that there is not yet evidence showing that this mechanism occurs in live hosts. For those that really want to get alarmed, he also calls attention to a recent Nature Microbiology paper describing a hybrid plasmid with both MCR-1 and resistance to carbapenem, another antibiotic.
Posted on October 18, 2016 by
A diagnostic test used by hospitals says a recently isolated strain of bacteria is susceptible to the “last resort” antibiotic colistin. But the strain actually ignores treatment with colistin, causing lethal infections in animals.
Through heteroresistance, a genetically identical subpopulation of antibiotic-resistant bacteria can lurk within a crowd of antibiotic-susceptible bacteria. The phenomenon could be causing unexplained treatment failures in the clinic and highlights the need for more sensitive diagnostic tests, researchers say.
In Nature Microbiology (published online Monday, May 9), scientists led by David Weiss, PhD, describe colistin-heteroresistant strains of Enterobacter cloacae, a type of bacteria that has been causing an increasing number of infections in hospitals around the world.
“Heteroresistance has been observed previously and its clinical relevance debated,” Weiss says. “We were able to show that it makes a difference in an animal model of infection, and is likely to contribute to antibiotic treatment failures in humans.”
Weiss is director of the Emory Antibiotic Resistance Center and associate professor of medicine (infectious diseases) at Emory University School of Medicine and Emory Vaccine Center. His laboratory is based at Yerkes National Primate Research Center. The co-first authors of the paper are graduate students Victor Band and Emily Crispell.
Posted on May 13, 2016 by