Shigella is a species of gut bacteria that causes diarrhoea in humans. It’s estimated that around the world the disease infects 80– 165 million, and kills 600,000 people every year. However, in the antibiotic era options to treat it are becoming scarcer, as the germ starts to develop resistance to treatment including ampicillin and tetracyclines. In the most severe cases, when all other drugs aren’t fighting the disease, doctors administer colistin – the last resort antibiotic. This week research published in Applied and Environmental Microbiology, a journal of the American Society for Microbiology, has reported that the bacteria have evolved to carry mcr-1 – the drug-resistant gene that protects the pathogen from colistin. The researchers screened 2,000 Shigella samples, from patients, the environment, and animal faeces, and found that one sample was positive and carried the gene as a transferable plasmid. The findings are alarming because plasmids are mobile bits of genetic information that can be easily passed from one bacterium to another, even crossing species, and carrying the trait to the new host. The team have reported, “Isolation of plasmid-mediated colistin resistance in S. flexneri from animal feces on a farm suggests that it is circulating via the fecal-oral route at least amongst animals on that farm, and possibly further afield via the food distribution network,” Once again bacteria have proven their ability to evolve and stay one step ahead of our defences.
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