Last month doctors reported that a strain of antibiotic-resistant E. coli had infected a 49-year-old woman in Pennsylvania. The alarming case is the first time scientists have found bacteria carrying mcr-1, a gene resistant to the drug colistin, in the United States.

“It is the end of the road for antibiotics unless we act urgently,” said Thomas Frieden, the director of the Centers for Disease Control and Prevention, in a speech at The National Press Club.

Colistin is typically a last-ditch treatment option for people infected with multidrug-resistant bacteria. Doctors successfully treated the Pennsylvania woman with a different kind of antibiotic, but that approach may not work for every patient.

The case, reported in Antimicrobial Agents and Chemotherapy on May 26, is alarming because of the potential for the resistant bacteria to spread. Until November 2015, when doctors reported a similar case in China, all known colistin resistance was due to DNA mutations within chromosomes—a kind of resistance not easily spread to other strains of bacteria.

But researchers found the new strain of E. coli did not become resistant through typical chromosomal mutations but by acquiring a plasmid, a circular unit of DNA that replicates within a cell but outside of chromosomes. Plasmids are easily transferable to other bacteria and carry instructions bacteria can use to protect themselves from antibiotics.

Meanwhile, researchers continue to study the use of bacteriophages, viruses that infect and destroy bacterial cells. The biopharmaceutical company AmpliPhi Biosciences is currently testing a phage-based antibacterial therapy that would treat drug-resistant infections. It expects to report final data on first-stage human trials later this year.

Genes on nicotine

Scientists have long known of a link between maternal smoking during pregnancy and later attention and behavioral problems in children. But the mechanism by which smoking causes these problems has been unclear.

Now researchers have found evidence that nicotine exposure before birth can trigger widespread genetic changes.

During a study published in Nature Neuroscience on May 30, the researchers exposed mice to nicotine, both in utero and during the initial postnatal period. The mice subsequently showed behavioral problems that mimicked the symptoms of attention deficit disorder in humans.

The researchers found that nicotine had impaired genes in the mice essential to the creation of synapses, brain connections that permit nerve cells to pass signals to one another.

When the scientists blocked the effects of the nicotine, the mice showed normal attention ability. —J.B.

Preemie improvements

Very premature babies have a better chance of surviving outside the womb than ever before, thanks to medical advances. A new study shows that the age of viability, considered by many doctors to be about 24 weeks of gestation, may now be closer to 22 weeks.

German researchers, publishing in JAMA Pediatrics on May 23, found that 67 percent of babies born at 22 to 23 weeks of gestation and given active medical care survived until hospital discharge.

The new research shows an even higher survival rate than that reported one year ago. A study published in The New England Journal of Medicine in May 2015 found that 23 percent of babies born at 22 weeks and one-third of babies born at 23 weeks survived with treatment.

The improved survival rates could also save some babies from abortion: Many states legally ban most abortions at the point of fetal viability. —J.B.