The group, led by Professor Jose Vazquez-Boland, has shown that one particular antibiotic ? fosfomycin ?can treat Listeria in the body, despite it being ineffective in laboratory conditions.
Because it was not effective in the laboratory, this drug has never been considered for the treatment of listeriosis, in spite of it reaching the infection sites more effectively than other antibiotics.
Professor Vazquez-Boland said: "Our results illustrate that antibiotic resistance in the laboratory does not always mean that the drug will not work in the infected patient. This work brings some optimism to the highly worrying problem of the increasing resistance to antibiotics."
The Listeria bacteria causes the food-borne disease, listeriosis. It often triggers a brain infection and kills up to 30% of those affected.
To test whether antibiotics are effective, bacteria are taken from patients and tested in the laboratory. These tests measure whether antibiotics can halt the growth of Listeria in laboratory conditions. Such tests are usually a measure of how effective the drug will be in the body.
When tested this way, Listeria had been shown to be resistant to the antibiotic, fosfomycin. As a consequence, this drug has never been considered for the treatment of listeriosis.
Dr Mariela Scortti, lead author on the paper, added: "Our findings warn about the need to revise laboratory methods currently in use to determine the susceptibility or resistance of bacteria to such drugs, so that the tests reflect better what actually happens in the body."