One of the most common infections may become deadly in a post-antibiotic world. Almost half of all women will acquire a urinary tract infection (UTI) at least once in their lifetime. Normally, antibiotics are highly effective in treating UTIs. But without antibiotics, the infection can spread into the kidneys or the bloodstream, causing severe illness. Now, a new list released by the World Health Organization indicates that E. coli , a leading cause of UTIs, is becoming resistant to some antibiotics. Here’s Debora MacKenzie, reporting for New Scientist:

The WHO’s list is aimed at a G20 meeting in Berlin, Germany, at which the world’s twenty richest countries will discuss how to pay pharmaceutical companies to develop new antibiotics, which are otherwise too unprofitable to invest in . Priorities need to be spelled out, says Nicola Magrini of the WHO, partly because what work is being done on new antibiotics is largely aimed at the bacteria for which it is easiest to find and test new drugs, not those doing the most damage.

Researchers at the WHO and at the University of Tübingen, Germany, pinpointed the most damaging families of drug-resistant bacteria based on criteria such as how often bacteria resist antibiotics, how many they resist, how often they kill, and the numbers of people affected.

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As more drugs become powerless in the face of bacteria like E. coli, we may experience an unprecedented wave of epidemics. “In many ways, a hospital acquired infection has become more serious than an uncontrolled bleed,” Jenny Morber reported for NOVA Next last May. For UTIs in particular, intravenous injection of the antibiotic colistin is a last-ditch option—but resistance to colistin is emerging in India and China. Scientists believe that colistin resistance might have developed because farmers are using the drug as a growth promoter in livestock, as we noted earlier this month:

Flies at poultry farms in China were loaded with bacteria containing genes for antibiotic resistance, the team discovered. The same team also found E. coli containing mcr-1 , a gene that imparts resistance to colistin, an antibiotic of last resort, in 1% of hospital patients in two of China’s large cities, neither of which have a history of using colistin to treat humans. They also discovered in the hospitals genes that offer resistance to carbapenems, another class of last-resort antibiotics.

Researchers think the flies carried the bacteria from farms to cities, where they transmitted the bacteria to humans. Carriers like these flies could be more commonplace, suggesting the need for experts to keep a watchful eye on superbugs’ paths.

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