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Seagulls Are Carrying a Dangerous Superbug Through the Skies

A European Herring Gull (Larus argentatus) takes off.
A European Herring Gull (Larus argentatus) takes off.
Photograph by Ben Cranke

A superbug that’s resistant to the absolutely last-ditch antibiotic colistin has been reported in seagulls on two continents—pinpointing one way, though almost certainly not the only way, that this dangerous drug resistance is moving around the world.

Since last November, when researchers in England and China announced the discovery of bacteria able to survive colistin, there has been an explosion of people looking for that resistance, and finding it. Scientists have published almost 100 reports of colistin resistance—known as MCR and conferred by a gene that’s been dubbed mcr-1—in almost two dozen countries.

It has been found in human patients, including a woman in the United States in May; in livestock, which get the drug on intensive farms, and are probably the original source of the problem; and even in pets.

Now, in letters to the Journal of Antimicrobial Chemotherapy, two research teams in Lithuania and Argentina report that they trapped birds and swabbed their butts, or scooped up seagull droppings, and found the resistance-conferring gene in E. coli being carried by two species: herring gulls in Lithuania (Larus argentatus) and kelp gulls in Argentina (Larus dominicanus). 

Both teams think the birds probably picked up the resistant E. coli by eating garbage, which may have contained sewage or medical waste. (The organisms in the South American gulls also contained another important type of antibiotic resistance, known for short as ESBL.)

This isn’t the first time that gulls have been identified as possible carriers of antibiotic-resistant bacteria. In 2011, French researchers found multi-drug resistant E. coli in seagull droppings in Miami Beach, and those researchers and others earlier found resistant bacteria in gulls in Portugal, France, Russia, and Greenland.

The point in all those stories, as well as in the new reports, is that gulls migrate, from hundreds to thousands of miles depending on the species—so they could serve as a vehicle for carrying resistant bacteria somewhere new.

Gulls migrate, from hundreds to thousands of miles, so they could serve as a vehicle for carrying resistant bacteria somewhere new.

“The lifestyle of gulls allows them to carry and disseminate pathogenic and resistant microorganisms despite country borders,” the Lithuanian researchers say in their report. “Water contaminated by feces of birds should be foreseen as an important risk factor for transmission of resistant bacteria.”

The undetected movement of bacteria is especially important in the case of MCR, because the discovery of colistin resistance is truly alarming. Colistin is an old drug that medicine consigned to the back of the shelf in the 1950s because it is toxic, and only recently started using again because so many other antibiotics have been undermined by overuse in medicine and agriculture.

The gene that creates colistin resistance is on what is called a plasmid, a loop of DNA that isn’t bound up in chromosomes but can move easily between bacteria. That has scientists worried that the gene could move into disease organisms that already possess resistance to other antibiotics, creating a superbug that would be completely untreatable.

Kelp gull (Larus domicanus) perched on rock, Caldera, Chile.
Kelp gull (Larus domicanus) perched on rock, Caldera, Chile.
Photograph by Chris Mattison

So far, mcr-1 has been found in the United States three times: in two stored samples from slaughtered pigs that were stashed in a U.S. Department of Agriculture database, and in a 49-year-old woman in Pennsylvania, not identified by name, who went to a clinic for help with a urinary tract infection.

At a meeting Tuesday afternoon in Washington, D.C., of the Presidential Advisory Council on Combating Antibiotic-Resistant Bacteria, federal officials relayed that the woman has recovered from her infection, but still continues to carry the highly resistant bacterium in her system. Dr. Beth Bell, director of the National Center for Emerging and Zoonotic Diseases at the Centers for Disease Control and Prevention, also said that 99 of the woman’s family members and close contacts have been checked, and none of them are carrying bacteria containing mcr-1, reinforcing the mystery of how the resistant bacteria reached her.

Bell and representatives of the U.S. Department of Agriculture said the gene remains rare in the U.S.: The CDC has checked more than 55,000 stored samples collected from patients, animals, and food, and the USDA is checking 2,000 additional samples that it has stored. So far, that search has revealed only the two samples from pigs that were slaughtered in Illinois and South Carolina.

The officials commenting Tuesday agreed that there may be no way of tracing the path that MCR took to reach the U.S.—the bacteria may have spread from another person, or on food—and that the key thing now is to build surveillance systems that alert health planners as it moves.

“The good news is we found it,” observed Dr. Martin Blaser, a professor of medicine and microbiology at NYU Medical Center and chair of the Presidential council. “The bad news is, it’s here.”

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Why It’s Crucial the New Superbug Was in a Urinary Tract Infection

Escherichia coli bacteria live in the intestines of humans and are a common cause of urinary tract infections.
Escherichia coli bacteria live in the intestines of humans and are a common cause of urinary tract infections.
Janice Haney Carr, Centers for Disease Control and Prevention

The alarm over the arrival of a grave new superbug in the United States is obscuring part of the story that is crucial to understanding what might happen next. Here it is: The woman who was carrying an E. coli containing resistance to the last-resort antibiotic colistin went for medical care because she had what felt like a routine urinary tract infection, a UTI for short.

The discovery of colistin-resistant bacteria is worrisome: Researchers have been watching for the arrival of this new superbug  for several months. But that it was found in  urine sample puts the discovery into a larger context. Highly drug resistant urinary tract infections happen potentially hundreds of thousands of times a year just in the United States. A small, dedicated corps of researchers has been trying for years to emphasize that these infections represent a serious danger, an unexamined conduit of bacterial resistance from agriculture and meat into the human population, and have mostly been dismissed.

Now that the new-new superbug has thrown light on the problem, will someone listen?

The Centers for Disease Control and Prevention weighed in Tuesday with a statement and a press briefing with health officials from Pennsylvania, where, last week, military researchers said they found the mcr-1 gene in an E. coli bacterium carried by a woman living there.

There are up to 8 million urinary-tract infections in the U.S. each year, and probably at least 10 percent, or 800,000, are antibiotic-resistant.

The MCR gene is important because it represents a breach in the last line of antibiotic defense: It confers protection against colistin, one of the oldest antibiotics out there, and one of the few that continues to work even against bacteria that resist multiple other drugs. Colistin was seldom used in people until recently because it is toxic, but agriculture has been using it enthusiastically for decades, which has seeded resistance through the bacterial world.

And those highly drug-resistant bacteria are turning up in urinary-tract infections. Why UTIs? Because E. coli bacteria are carried in feces, which can easily spread to the urethra and cause urinary-tract infections, especially in women. I’ve written about this several times; the long version in MORE magazine, and, even longer, in a collaborative investigation between the Food and Environment Reporting Network, the Atlantic, and ABC News.

The short version is this: Up to 8 million urinary-tract infections occur in the United States each year, and each year, a growing and significant proportion—hard to measure, but probably at least 10 percent, or 800,000—are antibiotic-resistant.

This has been happening with such frequency that it has actually changed medical practice. Medical specialty societies have been advising doctors for several years now that they should always do a test to determine which antibiotic will work for a UTI, rather than prescribing based on a standard checklist.

But only a few researchers have investigated why that tide of resistance is rising. What they have found is that these resistant UTIs infections are not random and singular, but instead constitute a focused epidemic, caused by particular sets of E. coli that bear the same resistance signatures as ones found in meat animals given antibiotics.

This idea has had difficulty gaining traction, because UTIs are usually dismissed as a minor problem, something that causes a few days of annoyance and requires a few days of antibiotics to fix. (And, not coincidentally, because they overwhelmingly happen to women.) But when UTIs go untreated—which is effectively what happens when the antibiotic administered for them doesn’t work —they climb up the urinary system from the bladder, into the kidneys, and thence into the bloodstream.

At that point, the minor problem becomes literally life-threatening. And resistant UTIs are not only a problem for the individual sufferer: They also pose the possibility of infecting others, if the original victim goes into a hospital for treatment and carries the resistant organism unrecognized in their system.

One reason it has taken so long to recognize this problem is that there is no single surveillance network that could capture all the resistance patterns in all those UTI sufferers, and compare them. There is also the problem of belief: It’s just difficult to imagine that something as minor as a UTI could be the signal of something as grave as a widespread epidemic.

Because of that, the MCR finding in Pennsylvania could end up being fortunate—no only for detecting a grave development early, but also for shining a light on a danger that has been growing, unrecognized, for a while.