Harvard Study: Drug-Resistant “Nightmare Bacteria” Show Troubling Ability to Diversify and Spread

Researchers examine carbapenem-resistant Enterobacteriaceae

A family of highly drug-resistant and potentially deadly bacteria may be spreading more widely—and more stealthily—than previously thought, according to a new study from Harvard T.H. Chan School of Public Health and the Broad Institute of MIT and Harvard. 

Researchers examined carbapenem-resistant Enterobacteriaceae (CRE) causing disease in four U.S. hospitals. They found a wide variety of CRE species. They also found a wide variety of genetic traits enabling CRE to resist antibiotics, and found that these traits are transferring easily among various CRE species. The findings suggest that CRE is more widespread than previously thought; that it may be transmitting from person to person asymptomatically; and that genomic surveillance of these dangerous bacteria should be increased.

The study was published online in the Proceedings of the National Academy of Sciences.

“While the typical focus has been on treating sick patients with CRE-related infections, our new findings suggest that CRE are spreading beyond the obvious cases of disease. We need to look harder for this unobserved transmission within our communities and health care facilities if we want to stamp it out,” said senior author Dr. William Hanage.

CRE comprise a class of bacteria that resist multiple antibiotics, including carbapenems, which are considered last-resort drugs when other antibiotics have failed. CRE, which tend to spread in hospitals and long-term care facilities, cause an estimated 9,300 infections and 600 deaths in the United States each year, according to the U.S. Centers for Disease Control and Prevention—and incidence is on the rise. CDC Director Dr. Tom Frieden has called CRE “nightmare bacteria” because they are resistant to some of the last-ditch treatments available to doctors battling resistant infections.

The researchers looked at approximately 250 samples of CRE from hospitalized patients at three Boston-area hospitals and one California hospital. Their goals were to obtain a snapshot of the genetic diversity of CRE; to define the frequency and characteristics of outbreaks; to find evidence of strains being transmitted within and between hospitals; and to learn how resistance is being spread among species. Previous studies have typically examined just one outbreak at a time.

The researchers found what Hanage termed a “riot of diversity,” both among CRE species and among carbapenem resistance genes. They also found that resistance genes are moving easily from species to species, contributing to a continually evolving threat from CRE.

In addition, the researchers found resistance mechanisms that hadn’t been seen before—implying that there are more to be discovered. This finding highlights the need for vigilance in searching for as-yet unknown forms of resistance as they evolve and emerge.

Source: Harvard T.H. Chan School of Public Health; January 16, 2017.