Sewage from
airplanes serves as a melting pot for a globally sourced group of gut microbes.
Now, a study suggests that such waste is loaded with bacteria resistant to antibiotics along with a
smorgasbord of genes that confer drug resistance. That means airplane waste
could be helping to fuel the spread of antibiotic resistance around the world.

In a survey
of airplane sewage from five German airports, around 90 percent of 187 E. coli isolated and tested were
resistant to at least one antibiotic. For comparison, between 45 and 60 percent
of these common gut dwellers collected from inlets to German wastewater
treatment plants were drug resistant, the scientists found. And E. coli from airplane sewage was far
more likely than that from municipal wastewater to be resistant to three or
more antibiotics, researchers report in the Dec. 3 Environmental Science & Technology.

“This is
really important work,” says Amy Pruden, an environmental engineer at Virginia
Tech in Blacksburg who was not involved with the study. “You read it, and you
think, ‘somebody should have done this sooner.’”

When
microbes are resistant to multiple drugs, it can make infections difficult to treat or even deadly (SN: 8/16/19). A recent government report estimates that infections
of drug-resistant fungi and bacteria claim about 35,000 lives in the United States every year (SN: 11/13/19).

Scientists
and public health officials have tended to focus on hospitals as places where these
“superbugs” can arise. But people may want to pay special attention to how
airport sewage is contained and treated, Pruden says. In this study, airplane sewage E. coli far surpassed drug resistance reported for microbes sampled
in German hospitals. The airplane sewage had eight times the prevalence of E. coli resistant to three specific drug
classes used to treat urinary tract infections caused by this microbe.

“This study
clearly shows that the antibiotic-resistance problem is a global problem, and a
global effort is necessary to tackle this severe threat for human and animal
health,” says study coauthor Stefanie Hess, a microbiologist at Technische
Universität Dresden in Germany.

Along with
more resistant microbes, the abundance and diversity of genes that let microbes
evade antibiotics were higher in airport sewage than in municipal waste. For
some classes of drugs, there were around 10 times as many copies of resistance genes
for a given number of microbes.  When the
mélange of microbes in airport sewage mingles, they may trade these genes.

Antibiotic-resistance
genes have a “particularly scary ability,” says microbiologist Carlos
Amábile-Cuevas of the Lusara Foundation, a private, nonprofit research
institution in Mexico City, who was not involved with the work. They can
shuffle around in the DNA of individual bacterial cells and then move from one
bacterium to another, he says.

In this
work, the researchers didn’t find a higher instance of antibiotic-resistant
microbes in wastewater treatment plants that received airport waste compared
with plants that didn’t. Amábile-Cuevas says this is because the airport waste
is a tiny fraction of what a wastewater treatment plant may receive from a
city.

“This
doesn’t mean that these bugs aren’t there,” Amábile-Cuevas says. “There may be
much more resistant bugs in the wastewater … but they are just below our
detection range. And this is also very scary.”

Scientists
previously have shown that drug-resistant bacteria and resistance genes can
enter the environment with treated wastewater. There, in receiving rivers,
bacteria can pass along drug resistance to other microbes. Researchers including
Amábile-Cuevas are looking at ways that wastewater treatment can reduce these
genes and microbes.

Drug
resistance also is known to travel and spread with migrating birds, traveling people and
traded food
(SN: 6/14/19). This study adds to the evidence of how
mobile antibiotic resistance is, Amábile-Cuevas says. It shows that even if an
area carefully controls antibiotic use and disposal, it could still end up with
antibiotic resistance thanks to a nearby airport. Some might think resistance
can be controlled by containing it within a city or country, “but this is
really not true at all,” he says.

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