MCR-1

The more researchers look for colistin-resistant bacteria, the more they find

lborkowski — Mon, 01 Aug 2016 07:48:22 +0000

The more researchers look for colistin-resistant bacteria, the more they find

Last year, researchers identified a gene that confers resistance to "last-resort" antibiotic colistin. They found it in several E. coli isolates in China, and it didn't take long for other researchers around the world to find the same gene, mcr-1, in stored samples once they started looking for it. Researchers have now found mcr-1 in isolates from 32 countries.

The US wasn't among the initial list of countries finding mcr-1, but it didn't take long for that to change. In May, Walter Reed Army Institute of Research scientists reported finding mcr-1 in E. coli cultured from the urine of a Pennsylvania woman with symptoms of a urinary tract infection. Then in July, researchers from JMI Laboratories reported finding the gene in an E. coli sample collected in May 2015 in New York. So, this gene has already been in the US for more than a year, and could continue to be found in stored US samples as more labs start looking for it.

Also in July, researchers from Belgium published an article in Eurosurveillance reporting their identification of another gene that confers colistin resistance; they dubbed it mcr-2. They studied isolates collected in 2011 and 2012 from calves and piglets with diarrhea. Out of 105 E. coli isolates, they found mcr-1 in 13. They then analyzed a selection of the remaining samples and identified mcr-2; returning to the 92 samples that did not have mcr-1, they found that 12 of them carried mcr-2.

Like mcr-1, mcr-2 has been found on a plasmid, a piece of DNA that can move easily between different bacteria -- though mcr-2 might even disseminate more quickly than mcr-1. This plasmid mobility makes it easier for bacteria to acquire resistance to multiple drugs. So far, the isolates with mcr-1 haven't carried resistance to all other antibiotic classes. But the ease with which mcr-1 can transfer makes it increasingly likely that we'll see it acquired by bacteria that are already resistant to the first- and second-line antibiotics.

As is often the case, the best explanation of these developments in antimicrobial resistance comes from Maryn McKenna at Germination. She also tacks on this alarming news:

And in a development that medicine has been braced for, Italian researchers say today that they have found yet another variant of the superbug gene, mcr-1.2, in a child hospitalized with leukemia in Florence. That variant, like mcr-1 and the newly named mcr-2, creates resistance to the very last-resort antibiotic colistin.

But what especially rang their alarm bells is that they found the gene in a strain of bacteria, Klebsiella pneumoniae, that was already resistant to the almost-last-resort antibiotic class, carbapenems, and to several other classes as well. Those bacteria are known by the acronym KPC, and since the early 2000s, they have spread through hospitals around the world. So the Italian discovery signals two things that medicine has feared: that MCR has landed in bacteria that are already good at spreading through healthcare, and that it has begun the process of stacking up in bacteria, alongside other resistance DNA, on the way to creating what could be a truly untreatable bug.

Better surveillance is important to continue to learn more about how widespread the problem is. To slow the emergence and spread of antibiotic resistance, though, the most important thing to do is to halt the routine use of antibiotics in livestock production.

lborkowski Mon, 08/01/2016 - 03:48

MCR-1 and a Post-Antibiotic Future

milhayser — Tue, 14 Jun 2016 14:34:11 +0000

MCR-1 and a Post-Antibiotic Future

The first observation of a bacterial gene called MCR-1 in the United States has scientists worried, if not surprised. The gene provides resistance to colistin, an antibiotic with nasty side effects used to combat multidrug-resistant bacteria. On Aetiology, Tara C. Smith writes "colistin has seen a new life in the last decade or so as a last line of defense against some of these almost-untreatable infections." But now, bacteria wielding MCR-1 threaten to leave humans defenseless. On The Pump Handle, Liz Borkowski explains "MCR-1 is of particular concern because it’s carried on a plasmid, a small piece of DNA that can easily transfer from one strain of bacteria to another." This raises the specter of future pathogens resistant to all known antibiotics. As Smith writes, "I’m not an advocate of panic myself, but I do think this is yet another concern and another hit on our antibiotic arsenal."

milhayser Tue, 06/14/2016 - 10:34

US researchers find bacteria resistant to last-resort drug

lborkowski — Wed, 01 Jun 2016 13:04:30 +0000

US researchers find bacteria resistant to last-resort drug

Back in November, researchers from China reported finding a gene that confers resistance to the last-resort antibiotic colistin in several E. coli isolates, and warned that pan-drug resistant Enterobacteriaceae -- a family of bacteria that includes common foodborne illness culprits E. coli and Salmonella -- "is inevitable and will ultimately become global." As researchers in other countries began examining stored isolates for the gene, MCR-1, they found it. STAT's Helen Branswell reports it "has been found in many European countries, parts of Asia, North Africa, South America, and North America, including Canada."

Last week, researchers from the Walter Reed Army Institute of Research reported in Antimicrobial Agents and Chemotherapy that they've found MCR-1 in the U.S. Specifically, they identified it in E. coli cultured from the urine of a 49-year-old Pennsylvania woman with symptoms of a urinary tract infection. Patrick McGann and his co-authors note, "the patient reported no travel history within the prior 5 months." And they found the gene within three weeks of launching systematic efforts to look for it. Maryn McKenna reports at Germination:

The Pennsylvania woman’s diagnosis occurred thanks to a system set up within the DOD after MCR was discovered. Since last fall, any E. coli that was already resistant to a family of drugs known as ESBLs (extended-spectrum beta-lactams), as hers was, has been sent up the chain to Walter Reed, to be scrutinized for colistin resistance. That kind of systematic checking for antibiotic resistance, known as active surveillance, is rare in the United States. Most civilian surveillance systems are patchy; they focus only on foodborne illnesses, or rely on physicians or labs to report diagnoses, or draw from a few state health departments with already well-funded labs.

In addition to this discovery by the Department of Defense, an HHS.gov blog post reports, "A USDA and HHS search for colistin-resistant bacteria in food animals, retail meats and people also has found colistin-resistant E. coli in a single sample from a pig intestine." Over the past year, these three agencies have been involved in surveillance and research activities as part of President Obama's National Action Plan for Combating Antibiotic-Resistant Bacteria.

MCR-1 is of particular concern because it's carried on a plasmid, a small piece of DNA that can easily transfer from one strain of bacteria to another. While the bacteria from the Pennsylvania woman was susceptible to some antibiotics, the fear is that a separate multi-drug resistant bacteria -- like "nightmare bacteria" carbapenem-resistant Enterobacteriaceae (CRE) -- could acquire MCR-1. In other words, we could soon be facing bacteria that are resistant to all antibiotics currently available. In such a "post-antibiotics future," medical procedures that are now routine, like dialysis or hip replacements, could carry the risk of untreatable infections.

The fact that US agencies discovered MCR-1 in a human patient and animal sample is a sign of success for their new surveillance efforts. CDC and USDA are investigating possible sources of these infections and working to identify any other cases. Worldwide, surveillance efforts have succeded in identifying MCR-1 in samples from a variety of sources in several diffeent countries. Where we're lagging, though, is in adressing the root of the problem: inappropriate use of antibiotics. Lance Price of the Antibiotic Resistance Action Center (ARAC) at the George Washington University Milken Institute School of Public Health (where I also work) had this statement:

Much like in the U.S., Chinese livestock producers are overusing antibiotics to prevent diseases and make animals grow faster. Colistin is widely used in Chinese livestock and this use likely led to the evolution of mcr-1. This promiscuous gene can be transferred from bacterium to bacterium, increasing the likelihood that it will find its way to CRE. History shows that mobile resistance genes can spread quickly around the world, silently riding in people, animals, and food. We’re watching this scenario play out in real time.

Scientists rang the alarm bells about mcr-1 back in November, but the attention didn’t last much longer than an average news cycle. Now we find that this gene has made its way into pigs and people in the U.S. If our leaders were waiting to act until they could see the cliff’s edge—I hope this opens their eyes to the abyss that lies before us. It’s time to act. We need a global agreement to end the abuse of all medically important antibiotics in livestock production in the U.S. and around the world.

I wish I could express some optimism about the likelihood of US leaders responding to this threat with the force and urgency it deserves. But if our current Congress can't even approve sufficient funds for Zika virus response, when the virus is already circulating in Puerto Rico, I fear they won't consider the MCR-1 discovery to be the wake-up call it ought to be.

lborkowski Wed, 06/01/2016 - 09:04