Gene-Swapping Bacteria Are Making New Superbugs

Bacteria appear to be having the microbial equivalent of inter-species sex in hospital sinks, swapping chunks of DNA that render them impervious to antibiotics, researchers reported Wednesday.

The findings may help explain the rise in drug-resistant superbugs in hospitals, and they suggest that they may sometimes be breeding on site, as opposed to being carried in by patients.

The team at the National Institutes of Health found carbapenem-resistant Enterobacteriaceae (CRE) that appeared to have exchanged pieces of genetic material called plasmids that gave them resistance to antibiotics. CRE resist most, if not all antibiotics, and they are becoming more common: they are found in about 4 percent of hospitals now and 18 percent of long-term care facilities.

"Over the past decade, there has been a steady and alarming increase in antibiotic-resistant bacteria."

They found the superbugs on patients and in the sinks at the NIH clinical center outside Washington D.C., a large hospital that had a bad outbreak of drug-resistant Klebsiella in 2011 in which 17 patients got badly infected and six died.

They tested all the patients in two wards in 2012 and 2013 - 1,000 in all -- and found 10 patients colonized with CRE. There was clear evidence the germs were getting new plasmids from somewhere. More searching turned them up in sink drains, although theres no direct evidence thats where the patients got them from.

Antibiotic resistance is becoming a huge medical challenge. Antibiotic resistance is caused by resistance genes carried on plasmids, small circles of DNA separate from the chromosomal DNA. Resistance spreads by horizontal gene transfer, in which plasmid genes from a donor bacterial cell spread to a recipient bacterial cell during cell-to-cell contact. When the DNA that is transferred includes antibiotic-resistance genes, the bacterium receiving this DNA becomes antibiotic-resistant too.

It's also not clear where the bacteria are getting the new plasmids, says Julia Segre of the National Human Genome Research Institute, part of NIH.

Bacteria reproduce by splitting in half, but they can also exchange genetic material. This DNA exchange helps them evolve and can help them evolve resistance to antibiotics.

Over the past decade, there has been a steady and alarming increase in antibiotic-resistant bacteria, a trend that poses a serious threat to the U.S. medical system, Segre and colleagues wrote in their report, published in the journal Science Translational Medicine.

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Gene-Swapping Bacteria Are Making New Superbugs