A leading hospital has said it had stepped up cleaning and taken other measures after four premature babies were found to be infected with a superbug resistant to common antibiotics.
The babies at the neonatal unit of University College Hospital, London, were infected with so-called "gram-negative" bacteria known to be resistant to some antibiotics, a spokeswoman said.
One of the infants died with the infection, two died of other causes and a fourth has recovered, she said.
The babies were among 15 at the unit over six weeks found to be carrying several types of bacteria, of whom 13 had bacteria resistant to treatment with gentamicin, an antibiotic used to treat premature babies.
Of those, nine were carrying the bacteria on their skin and four were found to have it in their blood streams.
Minutes of a meeting at the hospital on August 10 seen by the Daily Telegraph said the number of cases of gram-negative bacteria found on the neonatal unit had prompted a "heightened level of concern".
A deep clean of the unit was completed and the primary antibiotic used to combat infections was changed.
A statement from University College London Hospitals (UCLH) NHS Foundation Trust said: "Development of antibiotic resistance is unfortunately a common occurrence for all neonatal units, even more so in units such as ours which care for the most premature babies.
"During July we became concerned because we found particular bacteria on routine surveillance (gentamicin resistant gram negative organisms). We responded accordingly, including increased cleaning and changing our routine antibiotics to those which we knew would kill these organisms."
The Health Protection Agency (HPA) said it had provided advice to UCLH in handling the recent cases of infection on the neonatal ward.