Three newborn babies died, and 12 others were infected, following an outbreak of a superbug in the intensive care unit at University College Hospital, London last month.
Records from an emergency meeting show that one premature baby died from a bacterial infection that doctors were unable to fight with antibiotics.
Two other babies also tested positive for antibiotic-resistant bugs after dying from complications relating to their premature birth.
And a fourth baby was found to have been infected with a bug resistant to gentamycin, which is the antibiotic used to treat premature babies. This baby is believed to have recovered, with a further nine babies found to be carrying gentamycin-resistant bugs.
Following the emergency meeting to discuss the outbreak on August 10, the unit, which treats some of the country's most vulnerable babies, has undergone an intensive clean, and no further cases have been reported.
Microbiologist Professor Hugh Pennington told the Daily Mail that antibiotic-resistant bugs were often the 'final straw' for very sick babies being kept alive by intravenous lines, ventilators and other equipment.
A a hospital spokesman 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 a particular bacteria on routine surveillance. We responded accordingly, including increased cleaning and changing our routine antibiotics to those which we knew would kill these organisms.'