A "vigorous" baby girl born prematurely died the next day from E coli, an inquest has heard.
Karly Farrell was born at 31 weeks and was not strong enough to fight the infection.
Swab tests revealed E coli present four days before birth but this was not made known to ward staff until she was born.
The inquest heard the Rotunda Hospital had implemented changes to the treatment of swab test results following her death.
However, Master of the Rotunda Professor Fergal Malone said the baby's treatment would not have changed, despite the delay.
Prof Malone said E coli in the vagina during pregnancy was common and not treated to avoid fostering an infection that became resistant to antibiotics.
The baby's mother, Louise McGuirk, from Swords, Co Dublin, had a swab test at the Rotunda on July 23. She was discharged and returned on July 26. Karly was born by caesarean at 8.37am on July 27.
The infant was described by the midwife as "vigorous" at birth. However her condition deteriorated and a diagnosis of septic shock was made.
Karly was treated with penicillin and gentamicin, both broad-spectrum antibiotics.
"E coli septicaemia is a terrifying entity with a 10 to 30pc mortality rate," said Dr Michael Boyle, a consultant in the neonatal unit. "She was the sickest baby we'd looked after for some time."
Karly developed multi-organ failure and died at 11am on July 28, the cause of death being E coli septicaemia.
"A premature infant who has E coli would find it very difficult to fight that infection," pathologist Dr Emma Doyle told Dublin Coroner's Court.
Prof Malone said prenatal swabs showing E coli were common, adding: "If found, it is not treated as you cannot eradicate it. The downside of treating it is you foster resistance."
New electronic systems at the hospital now return laboratory results directly to doctors.
"We are confident that error of not following up on a result will not happen again," he said.
Coroner Dr Myra Cullinane endorsed the changes and returned a narrative verdict.
"It is so sad. Really there's nothing can be said to parents who have lost a baby in this way," she said.