There was grim news over the last two weeks for anyone who values antibiotics as effective treatments for human infections. First came the results of a study from China, announcing the discovery of a gene (mcr-1) rendering E. coli resistant to the antibiotic colistin. The gene was identified and characterised in bacteria isolated from pigs after a sharp rise in colistin resistance was recorded. This is important for two reasons. Firstly, colistin is one of a group of antibiotics called polymyxins that are often used as a treatment of last resort for human infections resistant to most other antimicrobial drugs. Secondly, the mcr-1 gene was located on a plasmid – a piece of DNA not attached to the main bacterial genome – which means that it can easily be transferred horizontally to other bacterial cells, even those of another species. According to the Chinese research team, that suggests that colistin resistance is likely to spread rapidly through bacterial populations and become established worldwide, at least in part through the movement of animals and meat products along global food supply chains.
The second piece of bad news concerned studies by Danish scientists, who were investigating whether the mcr-1 gene could be detected in sequenced genomes of bacteria isolated in Denmark. They found it in five isolates from imported food samples and one from the blood of an infected hospital patient – evidence that the predicted spread of colistin resistance around the world is already under way. Hot on the heels of this news came the publication of a paper from an independent Review on Antimicrobial Resistance commissioned by the UK Prime Minister, which draws clear links between the overuse of antibiotics in food production and the development of resistant bacteria and recommends the introduction of global targets to severely limit that use.
Much of the media coverage of these events inevitably focused on the possibility that antibiotics will eventually become redundant as clinical drugs in humans as resistance to them increases. Indeed the UK independent Review estimates that around 10 million people each year could die from drug-resistant infections globally by 2050. But the World Health Organisation and other public health bodies point to the fact that people are already dying from untreatable infections, sometimes contracted from contaminated food. As I have pointed out many times, the problem of antibiotic resistance developing as a consequence of giving clinically important drugs to animals was first flagged up as long ago as the late 1960s. Yet we are still using vast quantities of antimicrobials as growth promoters in food animals. The Chinese researchers suggest that the addition of polymyxins to animal feed is a reason for the development of the mcr-1 gene they discovered. To its credit, the oft-maligned EU banned the use of all antibiotics as growth promoters in 2006. Surely the rest of the world must follow suit as soon as possible. No one wants to go back to the days when minor bacterial infections could often prove fatal, but some experts think it is already to late to avoid such an eventuality. A global ban on antibiotic growth promoters may not save the day, but at least it would be a positive step.