Salmonella bacteria can escape antibiotics and immune-system attack by hiding inside a host's immune cells.

Roland Regoes and Wolf-Dietrich Hardt of the Swiss Federal Institute of Technology in Zurich and their colleagues infected mice with Salmonella enterica and then treated the animals with the antibiotic ciprofloxacin. The team found that, after most of the infection had cleared from organs, about 10% of the Salmonella bacteria inside lymph nodes that drain the intestines were still viable and growing. These bacteria re-established infection after antibiotic treatment.

In a separate study, Sophie Helaine, David Holden, and their colleagues at Imperial College London found that Salmonella cells can also persist inside macrophages that ingest them. Molecules that stimulate certain types of immune cells could, in combination with antibiotics, improve treatment.

PLoS Biol. 12, e1001793 (2014); Science 343, 204–208 (2014)