Antibiotic-resistant organisms can be found in multiple
locations in a hospital – on countertops and doorknobs, on computers and in
sinks, and even inside the plumbing. To better understand how these organisms
spread, investigators at the National Institutes of Health (NIH) in Bethesda,
Maryland, recently collected samples from pipes beneath the hospital’s
intensive care unit and from outside manholes draining hospital wastewater. They
conducted whole-genome analyses on the samples to study the bacterial plasmids,
or rings of DNA, that can confer resistance to antibiotics. 

The majority of samples they studied from the pipes and sewers tested positive
for bacterial plasmids that confer resistance to carbapenems, the researchers
report this week in mBio,
an open-access journal of the American Society for Microbiology. The new
findings add to a growing body of evidence suggesting that the conduits of
hospital wastewater serve as a vast and resilient reservoir for plasmids that
can confer the genes responsible for antibiotic resistance.

Some scientists suggest that these populations flourish in waste because of the
common use of strong antibiotics in hospitals, which leads to an uptick in
antibiotic-resistant microbes in the sewers. Microorganisms compete for
survival in the environment, says NIH microbiologist Karen Frank, who co-led
the current study. “The bacteria fight with each other and plasmids can carry
genes that help them survive,” she says. As part of a complex bacterial
community, they can transfer the plasmids carrying resistance genes to each
other. That lateral gene transfer means bacteria can gain resistance, even
without exposure to the antibiotics.

Frank and her collaborators compared their data to five years’ worth of patient
data and samples collected from sinks and other high-touch areas, like
countertops, door knobs, and computers. Remarkably, the high prevalence of
carbapenem-resistant plasmids in the pipes and sewers wasn’t observed in parts
of the hospital to which patients had access. Of 217 samples analysed from
high-touch surfaces, only three (1.4%) tested positive for carbapenem-resistant
organisms. Similarly, of 340 samples collected from drains, only 11 (3.2%) were

That comparison suggests that surveillance efforts to watch for resistant organisms
are successful in minimising patient infections, even so close to a reservoir
of resistant bacteria, says Frank. “If you’re tracking resistant bacteria, you
might be able to prevent more infections in patients.” The comparison also
raises an important question, she adds. “How much should we care that there are
a bunch of plasmids down in the wastewater system if they’re not infecting our

Understanding the plasmid exchange and when the plasmids get into the pathogens
that infect our patients, she says, could help hospitals improve their
monitoring of resistance-conferring genes: “In the big picture, the concern is
the spread of these resistant organisms worldwide and some regions of the world
are not tracking the spread of the hospital isolates.”

In 2011, the US National Institutes of Health Clinical Centre (NIHCC) experienced
a cluster of infections of carbapenem-resistant Klebsiella pneumoniae. Using
whole genome sequencing, researchers traced the chains of transmission. That
analysis was led by Frank’s co-study leaders, epidemiologist Tara Palmore, also
at the NIH Clinical Center, and geneticist Julie Segre, at the National Human
Genome Research Institute. The analysis published in mBio, says Segre,
uses newer DNA sequencing technology that lets researchers compare microbes
from patients and the environment. 

Palmore says that the 2011 NIHCC outbreak led the hospital to institute
additional surveillance, including increased monitoring of high-risk patients
and regular sampling of the hospital environment. By knowing where the
resistance-conferring genes hide, she says, researchers have a better chance of
keeping them away from patients.


Reference: Weingarten
RA. Genomic Analysis of Hospital Plumbing Reveals Diverse Reservoir of
Bacterial Plasmids Conferring Carbapenem Resistance. mBio 9:e02011-17.