A "last-resort" antibiotic used when all other drugs fail is losing its effectiveness against a common hospital superbug, scientists have warned. Researchers at the University of Oxford studied Pseudomonas, a bacterium that often causes lung infections in hospital patients.
They exposed more than 900 populations of the bug to colistin, an antibiotic typically reserved for treating multidrug-resistant infections, according to the university.
The study, published in Cell Reports, found that a gene called pmrB, which is associated with colistin resistance, mutates at an unusually high rate. According to the researchers, this allows the bacteria to develop resistance much faster than previously expected.
Professor Craig MacLean said the findings reveal how quickly bacteria can become resistant to a clinically vital antibiotic, helping explain why colistin sometimes fails to treat patients effectively.
"Our work has shown that a gene involved in resistance to a last-resort antibiotic mutates at an incredibly high rate, allowing bacteria to quickly evolve antibiotic resistance," Professor MacLean said.
"Our research suggests that, in this particular case, selective pressures linked to this gene's role in helping bacteria evade the immune system may have driven the evolution of this unusually high mutation rate, enabling bacteria to rapidly become resistant to antibiotics."
There was some encouraging news. The researchers found that the bacteria quickly lost their resistance when the antibiotic was no longer present. The finding could help doctors determine how and when colistin should be used in hospitals.
Antibiotic-resistant infections already cause more than one million deaths worldwide each year. With very few last-resort antibiotics remaining, experts say the development of new treatments is becoming increasingly urgent.
