Researchers Discover Colistin-Heteroresistant Germs In the US (arstechnica.com)

An anonymous reader quotes a report from Ars Technica: For the first time, researchers have discovered strains of a deadly, multidrug-resistant bacterium that uses a cryptic method to also evade colistin, an antibiotic used as a last-resort treatment. That's according to a study of U.S. patients published this week by Emory University researchers in the open-access microbiology journal mBio. The wily and dangerous bacteria involved are carbapenem-resistant Klebsiella pneumoniae or CRKP, which are already known to resist almost all antibiotics available, including other last-line antibiotics called carbapenems. The germs tend to lurk in clinical settings and can invade the urinary tract, bloodstream, and soft tissues. They're members of a notorious family of multidrug-resistant pathogens, called carbapenem-resistant Enterobacteriaceae (CRE), which collectively have mortality rates as high as 50 percent and have spread rapidly around the globe in recent years. A 2013 report by the Centers for Disease Control and Prevention estimated that there were more than 9,300 CRE infections in the U.S. each year, leading to 600 deaths. Both the CDC and the World Health Organization have listed CRE as one of the critical drug-resistant threats to public health, in need of "urgent and aggressive action."

In the new study, the Emory researchers discovered two strains of CRKP -- isolated from the urine of patients in Atlanta, Georgia -- that can also resist colistin. But they do so in a poorly understood, surreptitious way. At first, they appear vulnerable to the potent antibiotic in standard clinical tests, but with more advanced testing and exposure to the drug, they reveal that they can indeed survive it. In mice, the strains caused infections that couldn't be cured by colistin and the mice died of the infections. Mice infected with typical CRKP were all saved with colistin. So far, there's no evidence of CRKP infections surprisingly turning up resistant to colistin during treatment in patients. But the authors, led by microbiologist David Weiss, say that may be because the evidence is difficult to gather, and the data so far is cause for concern. The researchers concluded that the findings "serve to sound the alarm about a worrisome and under-appreciated phenomenon in CRKP infections and highlight the need for more sensitive and accurate diagnostics."