A boy caught a strain of MRSA in hospital and died a month after suffering a head injury when he jumped off steps at school, a court has heard.
Kian Williams, aged three, had been at school for two terms
A pathologist told Mold Crown Court the head injury of Kian Williams, three, at a private nursery school in Bangor was not severe enough to crack his skull.
Michael Ashworth said the pneumonia was an MRSA type resistant to antibiotics.
Hillgrove School head teacher James Porter denies breaking safety laws. The case continues.
The jury has heard Kian, from Bethesda, was pretending to be Batman and was unsupervised in the playground when he was hurt jumping from the brick steps in July 2004.
The court was told Kian had landed face forwards, causing head injuries which led to a coma, then he developed pneumonia while in intensive care.
Dr Ashworth, who carried out the post mortem examination on Kian, confirmed to the court that Kian had died the following month from staphylococcal pneumonia, a form of MRSA.
Under cross-examination, Dr Ashworth said "there can be no doubt" the MRSA infection had caused the death.
The Health and Safety Executive is prosecuting the school's headmaster James Porter, 65, for an alleged safety breach.
The prosecution claims that Kian should not have been allowed unsupervised access to the steps.
On Monday, prosecuting counsel Nicholas Jones said there had been no physical barrier to the steps and only one teacher watching 59 pupils in both upper and lower playgrounds and she was unable to monitor the steps from she was.
Mr Porter, who also owns the school, denies that as an employer he failed to ensure as far as was reasonably practicable that pre-school age children were not exposed to the risk to their health by falling on a flight of steps.
Judge John Rogers QC has told the jury they would be visiting the school on Wednesday.