Disease

'Last-Resort' Antibiotics Fail Against New Superbugs

Some bacteria have finally breached the last wall of humans' antibiotic stronghold, according to a new study from China. In the study, researchers found a gene in one strain of Escherichia coli (E. coli) that protects these bacteria against one of the antibiotics considered to be a last resort. Moreover, this gene is easily transferred among microbial species, raising the possibility of multiple epidemics that doctors would be unable to treat.

When bacteria become resistant to even the last-resort antibiotics and can share that resistance with other types of bacteria, that leaves the human population extremely vulnerable to a range of infections that would be unstoppable.

In the study, the researchers found the gene, called mcr-1, in samples of E. coli that were taken from pigs, pork products and infected people. The gene protects the bacteria against an antibiotic called colistin. Mcr-1 was most common in the samples taken from animals, suggesting that it originated in livestock, the researchers said. In China, colistin is widely administered to livestock.

Animals that are raised for people to eat are routinely given antibiotics to protect the livestock against infection, and to stimulate their growth. But the constant presence of antibiotics in the livestock diet helps drive the increasing numbers of antibiotic resistant bacteria today, researchers say.

Colistin isn't a recent addition to the drug arsenal. It was discovered in 1947, and was used widely through the 1960s, but the drug had toxic effects on the kidneys and nervous system. Doctors mostly abandoned colistin after newer and safer antibiotics came along.

But sitting on the shelf for decades is exactly what kept colistin viable in the battle against drug-resistant bacteria. Because microbes had little exposure to colistin, they did not have much opportunity to evolve protection against it. As the list of effective antibiotics has shrunk, colistin has remained one of the last reliable lines of defense against bacterial infection.

That is, until now. In the new study, the researchers found the gene for colistin resistance in bacterial structures called plasmids, which are small circles of DNA that are easily passed from one bacterium to another, and even between different bacterial species.

Researchers have long known that the use of antibiotics, in both agriculture and in medicine, has encouraged bacteria to do what they've excelled at for more than 3 billion years: evolve and survive.

The new drug-resistant bacteria have not been found outside of China, the investigators said. But the researchers warned there is a strong possibility this drug-resistance gene could spread.

Right now, preventing bacterial infections with measures such as vaccinations and good hand hygiene are more vital then ever. He noted that antibiotics are useful only against bacterial infections, and that taking antibiotics when they're not needed just gives bacteria another chance to beef up their drug-resistant defences.