A particularly dangerous type of CRE bacteria is on the rise in the U.S. (Courtesy of CDC) 
 
 This post has been updated. 
 
 A particularly dangerous superbug, dubbed the "phantom menace" by scientists, is on the rise in the United States, according to a report Thursday by the Centers for Disease Control and Prevention. 
 
 This superbug's strains belong to the family of bacteria known as CRE, which are difficult to treat because they are often resistant to most antibiotics. They are often deadly, too, in some instances killing up to 50 percent of patients who become infected, according to the CDC. Health officials have called CRE among the country's most urgent public health threats. 
 
 The target of Thursday's report is relatively new. Unlike more common types of CRE, it carries a plasmid, or mobile piece of DNA, with an enzyme that breaks down antibiotics. And what makes these bacteria even more dangerous is their ability to transfer that plasmid--and that antibiotic resistance--to normal bacteria that are present in our bodies. 
 
 [Amid superbug worries, these states have the highest antibiotic prescribing rates] 
 
 This type of CRE has had a lower profile because it's actually less antibiotic-resistant than other more common types of CRE. As a result, it hasn't been a frequent focus of testing and has largely escaped detection by health officials, prompting some researchers to dub it "the phantom menace." 
 
 "This is a tricky drug-resistant bacteria, and it isn't easily found," CDC Director Thomas Frieden said in an interview. "What we're seeing is an assault by the microbes on the last bastion of antibiotics." 
 
 Bacteria develop antibiotic resistance in two ways. 
 
 Many can evolve their own genome in ways that deactivate antibiotics, although that ability can't be shared with pathogens outside their own family. 
 
 Yet other bacteria rely on a shortcut: They get infected with a plasmid carrying the resistance gene. That makes them more dangerous because plasmids can make copies of themselves and transfer within a family of bugs and as well as jump to other families of bacteria, which can then "catch" the resistance directly without having to develop it through evolution. 
 
 In a related alarming development, Danish researchers announced Thursday that a dangerous new superbug gene discovered in China two weeks ago had been found in bacteria infecting one person in Denmark. The gene makes the bacteria resistant to colistin, the antibiotic of last resort. And similar to the 'phantom menace' type of CRE, the gene is contained in a plasmid. 
 
 Experts warned that the latest development was frightening. "History shows that these mobile resistance genes can spread around the world quickly, silently riding in people, animals and food," said Lance Price, director of the Antibiotic Resistance Action Center at George Washington University's Milken Institute of Public Health, in a statement. 
 
 He said the news that the superbug gene first found in China has now turned up in Denmark "suggests that this scenario is playing out in real time," he said. 
 
 [A superbug emerges in China] 
 
 CDC received reports counting at least 43 patients in 19 states with this type of CRE superbug between June 2010 and August 2015. All cases were confirmed by CDC. Although the numbers are relatively small, Frieden said they are "just the tip of the iceberg." There was one patient with this type of superbug in 2010 and 11 patients each year in 2013, 2014 and 2015. 
 
 Most U.S. clinical laboratories that test for CRE organisms wouldn't identify this particular type of bacteria because it's not part of standard testing. CDC changed its definition of the organism in January to help increase detection. 
 
 CRE stands for carbapenem-resistant Enterobacteriaceae. 
 
 Read more: 
 
 CDC says ‘nightmare bacteria’ a growing threat 
 
 Extra funding sought to fight antibiotic resistant bacteria 
 
 One day, doctors might prescribe viruses instead of antibiotics 
 
 White House opens antibiotic summit 
 
 Chipotle CEO pledges to make restaurants ‘safest place to eat.’ Here’s his plan. ||||| The Post's Lena Sun visited Walter Reed Army Institute of Research in Silver Spring, Md., where scientists there identified a strain of bacteria resistant to the last-resort antibiotic, colistin. The bacteria was found in a Pennsylvania woman. Microbiologist Patrick McGann explains how his team identified the gene that gives the bacteria this resistance (Monica Akhtar,Lena Sun/The Washington Post) 
 
 For the first time, researchers have found a person in the United States carrying bacteria resistant to antibiotics of last resort, an alarming development that the top U.S. public health official says could mean “the end of the road” for antibiotics. 
 
 The antibiotic-resistant strain was found last month in the urine of a 49-year-old Pennsylvania woman. Defense Department researchers determined that she carried a strain of E. coli resistant to the antibiotic colistin, according to a study published Thursday in Antimicrobial Agents and Chemotherapy, a publication of the American Society for Microbiology. The authors wrote that the discovery “heralds the emergence of a truly pan-drug resistant bacteria.” 
 
 [How these biomedical detectives identified the dreaded new superbug in U.S.] 
 
 Colistin is the antibiotic of last resort for particularly dangerous types of superbugs, including a family of bacteria known as CRE, which health officials have dubbed “nightmare bacteria.” In some instances, these superbugs kill up to 50 percent of patients who become infected. The Centers for Disease Control and Prevention has called CRE among the country’s most urgent public health threats. 
 
 Health officials said the case in Pennsylvania, by itself, is not cause for panic. The strain found in the woman is still treatable with other antibiotics. But researchers worry that its colistin-resistance gene, known as mcr-1, could spread to other bacteria that can already evade other antibiotics. 
 
 [Superbug known as ‘phantom menace’ on the rise in U.S.] 
 
 It’s the first time this colistin-resistant strain has been found in a person in the United States. In November, public health officials worldwide reacted with alarm when Chinese and British researchers reported finding the colistin-resistant strain in pigs and raw pork and in a small number of people in China. The deadly strain was later discovered in Europe and elsewhere. 
 
 In this Nov. 2015 video, Centers for Disease Control and Prevention director Dr. Thomas Frieden said that the CDC is committed to fighting antibiotic resistance. (YouTube/CDC) 
 
 “It basically shows us that the end of the road isn’t very far away for antibiotics — that we may be in a situation where we have patients in our intensive care units, or patients getting urinary-tract infections for which we do not have antibiotics,” CDC Director Tom Frieden said in an interview Thursday. 
 
 [1 in 3 antibiotics prescribed in U.S. are unnecessary] 
 
 “I’ve been there for TB patients. I’ve cared for patients for whom there are no drugs left. It is a feeling of such horror and helplessness,” Frieden added. “This is not where we need to be.” 
 
 Separately, researchers at the Agriculture Department and the Department of Health and Human Services reported that testing of hundreds of livestock and retail meats turned up the same colistin-resistant bacteria in a sample from a pig intestine in the United States. USDA said it is working to identify the farm the pig came from. 
 
 CDC officials are working with Pennsylvania health authorities to interview the patient and family to identify how she may have contracted the bacteria, including reviewing recent hospitalizations and other health-care exposures. The CDC hopes to screen the patient and her contacts to see if others might be carrying the organism. Local and state health departments also will be collecting cultures as part of the investigation. 
 
 ['A nightmare superbug': What is it? And what are the risks?] 
 
 The woman was treated in an outpatient military facility in Pennsylvania, according to a Defense Department blog post about the findings. Samples were sent to the Walter Reed National Military Medical Center for initial testing. Additional testing was done by a special Defense Department system that tracks multi-drug-resistant organisms. 
 
 Thursday’s study did not disclose further details about the Pennsylvania woman or the outcome of her case. The authors could not be reached for comment. A spokesman at the Pennsylvania Department of Health was not immediately available to comment on the case. 
 
 Pennsylvania Gov. Tom Wolfe (D) issued a statement saying his administration immediately began working with the CDC and the Defense Department to coordinate "an appropriate and collaborative" response. 
 
 [Feds ramp up efforts to deal with antibiotic resistance] 
 
 "We are taking the emergence of this resistance gene very seriously," he said, adding that authorities will take all necessary actions to prevent it from becoming a widespread problem with "potentially serious consequences." 
 
 Sen. Robert P. Casey Jr. (D-Pa.) said he is concerned about the reports. In a statement, Casey said he supported legislation for and participated in hearings about antibiotic-resistant bacteria, which he said “present an urgent public health problem that we must focus on intensively.” He said he planned to get a full briefing on the case in the coming days. 
 
 Colistin is widely used in Chinese livestock, and this probably led bacteria to evolve and gain a resistance to the drug. The gene probably leaped from livestock to human microbes through food, said Yohei Doi, an infectious-disease doctor at the University of Pittsburgh who has studied the problem. 
 
 This animated video from 2013 from the Centers for Disease Control and Prevention highlights the key points and graphics of the "Antibiotic Threats in the United States" report. (YouTube/CDC) 
 
 "Food handlers may be at higher risk," he said. In places like China, where live animal markets are often in close proximity to food stalls, it may be more likely for the bacteria to spread from animals to humans. 
 
 He and other experts in infectious diseases called for speedier action to curb the overuse of antibiotics in livestock worldwide. 
 
 "It's hard to imagine worse for public health in the United States," Lance Price, director of the Antibiotic Resistance Action Center and a George Washington University professor, said Thursday in a statement about the case. "We may soon be facing a world where CRE infections are untreatable." 
 
 Scientists rang the alarm bells about the gene in November, but not enough attention was paid. "Now we find that this gene has made its way into pigs and people, and people in the U.S.," Price said. "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." 
 
 Scientists and public health officials have long warned that if the resistant bacteria continue to spread, treatment options could be seriously limited. Routine operations could become deadly. Minor infections could become life-threatening crises. Pneumonia could be more and more difficult to treat. 
 
 Already, doctors had been forced to rely on colistin as a last-line defense against antibiotic-resistant bacteria. The drug is hardly ideal. It is more than half a century old and can seriously damage a patient’s kidneys. And yet, because doctors have run out of weapons to fight a growing number of infections that evade more-modern antibiotics, it has become a critical tool in fighting off some of the most tenacious infections. 
 
 Bacteria develop antibiotic resistance in two ways. Many acquire mutations in their own genomes that allow them to withstand antibiotics, although that ability can’t be shared with pathogens outside their own family. 
 
 [Scientists discover why pancreatic cancer resists chemotherapy drug] 
 
 Other bacteria rely on a shortcut: They get infected with something called a plasmid, a small piece of DNA, carrying a gene for antibiotic resistance. That makes resistance genes more dangerous because plasmids can make copies of themselves and transfer the genes they carry to other bugs within the same family as well as jump to other families of bacteria, which can then “catch” the resistance directly without having to develop it through evolution. 
 
 The colistin-resistant E. coli found in the Pennsylvania woman has this type of resistance gene. 
 
 Public health officials say they have been expecting this resistance gene to turn up in the United States. 
 
 “This is definitely alarming,” said David Hyun, a senior officer leading an antibiotic-resistance project at the Pew Charitable Trust. “The fact that we found it in the United States confirms our suspicions and adds urgency to actions we need to work on antibiotic stewardship and surveillance for this type of resistance.” 
 
 Late last year, as part of a broader budget deal, Congress agreed to give hundreds of millions of dollars to the federal agencies engaged in the battle against antibiotic-resistant bacteria. 
 
 The largest chunk of that money, more than $150 million, was slated to go to the CDC as part of an effort to build and strengthen capacity at state and local health departments to prevent and monitor superbug outbreaks. 
 
 Other funding went to the National Institutes of Health for research on combating antimicrobial resistance, as well as to an agency known as BARDA, which works on national preparedness for chemical and biological threats, including developing new therapies. 
 
 Read more: 
 
 Superbug investigation: 'It’s likely we will find more of these,' CDC says 
 
 What we know so far about the superbug in the Pennsylvania case 
 
 Fight against superbugs gets dramatic funding boost under congressional budget plan 
 
 Why the United States is so vulnerable to the alarming spread of Zika virus 
 
 7 things about vaccines and autism that the movie ‘Vaxxed’ won’t tell you 
 
 Is 10,000-steps goal more myth than science? Study seeks fitness truths through our phones and more 
 
 With Memorial Day and summer travel coming up, it’s time to get serious about Zika 
 
 Like our Health & Wellness page on Facebook for more science news about the ins and outs of the human body and mind, essays and advice. You can sign up here for our newsletter. ||||| This image shows two rod-shaped bacteria called Klebsiella pneumoniae that are resistant to treatment with the antibiotic drug called carbapenem. In this image, the mustard-colored bacteria are interacting with the green-colored human white blood cell. 
 
 Health experts are keeping a close eye on a type of antibiotic-resistant bacteria called CRE that, while still rare, has the potential to become more widespread in the United States. This type of bug includes some strains of Escherichia coli and other bacteria. 
 
 A new report released on Thursday said that in the past five years, researchers have identified 43 patients in the United States who became sick with infections from one type of CRE. (The name is an abbreviation for "carbapenem-resistant Enterobacteriaceae," meaning the bacteria are part of a group called Enterobacteriaceae and are resistant to treatment with antibiotics called carbapenems.) 
 
 These cases all involved CRE that share a particular method of defeating the antibiotics: they have enzymes called OXA-48-like carbapenemases that break down the drugs, said the report from the Centers for Disease Control and Prevention. Other types of CRE have different methods of resisting the antibiotic. [6 Superbugs to Watch Out For] 
 
 This particular type of CRE that is the focus of the new report is "noteworthy" because the enzyme that thwarts the antibiotic is encoded on a piece of genetic material called a plasmid, "which can actually move from one bacteria to another," said Dr. William Schaffner, an infectious disease specialist and professor of preventive medicine at Vanderbilt University Medical Center in Nashville, Tennessee, who was not involved with the CDC report. 
 
 At the moment, this whole group of CRE bacteria is of great interest to researchers, Schaffner told Live Science. 
 
 Recently, for example, researchers discovered bacteria in China whose plasmids give them resistance to an antibiotic called colistin, he said. Some doctors consider colistin one of the last lines of defense against certain "superbugs." 
 
 The bacteria found in China and the ones in the new report — which both have key resistance genes contained on plasmids — "are of greatest public health concern because of their potential for rapid global dissemination," the researchers wrote in the new report. 
 
 Still, Schaffner stressed that, at the moment, these infections are not something the general public needs to worry about. But microbiologists, public health officials and infectious disease specialists are paying attention, he said. 
 
 Researchers have seen a few small clusters of cases around the country, which indicate that the infection likely spread in a hospital, Schaffner said. 
 
 In the new report, the CDC researchers noted that many of the patients with this particular type of infection had recently traveled out of the country, with India being the most frequent travel destination. In addition, among the patients who reported traveling abroad, 16 had been hospitalized outside of the United States, the report said, suggesting that foreign hospitals are a potential source of some infections. 
 
 The CDC is also tracking infections that come from other types of CRE. For example, there have been 118 cases in the United States of infections involving a certain enzyme, different from the one found in the bacteria that are the focus of Thursday's report, the CDC said. 
 
 Carbapenems are not considered the last line of defense against Enterobacteriaceae infections, meaning that if these drugs don't work, there are still other antibiotics available. However, the emerging resistance is still concerning to experts. This resistance reduces the number of antibiotics that doctors can use to treat these infections, Schaffner said. Doctors need multiple antibiotics available, and the more options there are, the better, he said. 
 
 To reduce the problems associated with antibiotic resistance, doctors and patients need to join together to be more prudent about using antibiotics, Schaffner said. 
 
 Follow Sara G. Miller on Twitter @SaraGMiller. Follow Live Science @livescience, Facebook & Google+. Originally published on Live Science.
– The latest strains of antibiotic-resistant bacteria to give researchers sleepless nights aren't the most common—or even the most antibiotic-resistant—but they have an ability that could make them a serious danger to public health. They contain enzymes known as "OXA-48-like carbapenemases" that can break down antibiotics and transfer that ability to normal bacteria in the body through mobile pieces of DNA, reports the Washington Post. and Live Science. The enzymes have been nicknamed the "phantom menace" by researchers because they can be tough to detect. In a report issued this week, the CDC says it identified 43 cases in the US involving the superbug between June 2010 and August of this year, mainly involving people who had traveled overseas, though some cases are thought to have been transmitted in the US. "This is a tricky drug-resistant bacteria, and it isn't easily found," CDC Director Thomas Frieden tells the Post. "What we're seeing is an assault by the microbes on the last bastion of antibiotics." The number of cases is small but rising, Frieden says, warning that what has been detected so far could just be the "tip of the iceberg." An infectious disease specialist tells Live Science that while the bacteria shouldn't be a major worry for the general public right now, doctors and patients should be aware that the best way to combat antibiotic resistance is to try to be more sparing in the use of antibiotics. (A mutation spreading in China has prompted warnings of an "antibiotic apocalypse.")