‘Nightmare Bacteria’ Are More Diverse Than We Previously Thought

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Researchers call for greater vigilance and more testing to stop a group of bacteria that resists nearly everything doctors can throw at it.

By Nathan Collins

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(Photo: The Centers for Disease Control and Prevention)

A group of unusually antibiotic-resistant and often deadly bacteria is more diverse and more nimble than previously realized, underscoring the need for “an aggressive approach to surveillance and isolation,” researchers write today in Proceedings of the National Academy of Sciences.

The bugs collectively known as carbapenem-resistant enterobacteriaceae (CRE) were back in the news last week, when the Centers for Disease Control and Prevention reported a patient died in September after contracting one of the more common CREs, Klebsiella pneumoniae. Testing revealed the particular strain in question was resistant to 26 antibiotics, including all 14 available at the hospital where the woman had been treated, STAT’s Helen Branswell reported on Friday.

Generally, CREs infect hospital patients, often through inadequately cleaned medical equipment such as ventilators and catheters, although there are concerns CREs could spread beyond hospitals and doctors’ offices, a scenario that could well justify the nickname “nightmare bacteria.”

The Reno case “is the harbinger of future badness to come,” University of Minnesota professor of medicine James Johnson told STAT.

But exactly what “future badness” is heading our way isn’t entirely clear, an observation that led Harvard University associate professor of epidemiology William Hanage and 26 others to survey CREs in three Boston-area hospitals—Massachusetts General Hospital, Beth Israel Deaconess Medical Center, and Brigham and Women’s Hospital—and one in Irvine, California.

The survey indicated that CREs were more diverse than previously thought, and that there was relatively little transmission of strains between hospitals. In Boston, for example, there were 17 different CRE strains (spread across three species, K. pneumoniae, E. coli, and Enterobacter cloacae) but only five strains appeared in more than one hospital. Only two strains, one K. pneumoniae and one E. coli, were found in both Boston and Irvine. Further analysis revealed a substantial number of genes for antibiotic resistance, along with mechanisms that made it easy to transfer those genes between strains and species.

Such diversity is particularly surprising given the limited size of outbreaks, the researchers write. If not many people get infected, then bacteria don’t have as much time and opportunity to mutate and evolve—in which case, CREs shouldn’t diversify very much at all.

So how did they get diverse? One likely (and unsettling) possibility is CREs could spread from person to person without actually getting many people sick. It’s a bit counter-intuitive that such apparently dangerous bacteria could float around without being detected, but it’s hardly unprecedented. People can carry and transmit meningitis, for example, without themselves getting sick. And it would explain the genetic diversity issue: If a species of bacteria has spread more widely than we know, it could easily have grown more diverse as well.

It would be bad news indeed if CREs are spreading without getting that many people sick, since it makes tracking and preventing outbreaks more difficult. The solution, the authors write, is more testing and testing outside of hospitals. “[S]tudies based on … hospitalized patients alone are insufficient to fully identify and interrupt transmission; therefore, we must extend these studies further to include isolates from outside of … hospital settings and from asymptomatic carriers,” the team writes.

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