Drug-resistant strains of Pseudomonas aeruginosa are more deadly than we realised (Image: JUERGEN BERGER/SCIENCE PHOTO LIBRARY)

Becoming resistant to drugs gives bacteria superpowers, making them stronger and potentially more deadly.

Until recently, the opposite had been assumed to be true. The observation that resistant bacteria grow slower than usual had led to the belief that acquiring resistance genes interfered with other essential processes. In other words, drug resistance came at a cost to the bacterium.

But it is becoming increasingly clear that things are not that simple. “How could we explain the worldwide success of these antibiotic-resistant strains if antibiotic resistance is supposed to have a fitness cost?” says David Skurnik from Harvard Medical School in Boston, Massachusetts.


Together with his colleagues, Skurnik exposed mice to various strains of Pseudomonas aeruginosa, a bacterium that causes a range of infections, particularly in people with compromised immune systems. Some of the strains contained mutated genes that made them resistant to certain antibiotics. These strains were better than the non-resistant strains at colonising and surviving in the lungs of infected mice.

Similarly, resistant strains of the bacterium that causes cholera and Acinetobacter baumannii, a key perpetrator of hospital-acquired infections, were more successful at causing infection in mice and rabbits than their non-resistant counterparts.

No price to pay

The work adds to a growing body of evidence challenging the commonly held idea that acquiring resistance comes at a cost, says José Luis Martínez of the Spanish National Biotechnology Centre in Madrid.

Most efforts to tackle antibiotic resistance so far have focused on preventing the over-use of antibiotics. Part of the reason is that, theoretically, if we can minimise the use of these drugs, it should give non-resistant bacteria the chance to outcompete the supposedly weaker drug-resistant strains.

But Skurnik cautions that this is unlikely to be true in all cases: “Once they acquire antibiotic resistance, some bacteria will be more fit,” he says. “In a lot of cases, stopping over-prescription will not be the easy way out.”

In addition, we should concentrate on developing new approaches to tackling resistance, rather than drugs that simply kill the bacteria, he says. Examples are therapies that harness the power of the immune system to combat infection, such as antibodies and vaccines.

Journal reference: Science Translational Medicine, DOI: 10.1126/scitranslmed.aab1621