She had rushed him to the hospital on September 2 after he collapsed at their home but doctors struggled to diagnose what was wrong with him.
Throughout his stay the boy, who battled with severe asthma, became extremely unwell and experienced fever, delirium and rigors – or shaking.
The Crown case hinged on the discovery of the bacteria in one blood culture sample in late September 2014, and evidence from concerned nurses who heard the distressed child ask his mother "why are you poisoning me?" during an emergency response.
The court heard the woman, a mother of four, has always vehemently denied the allegations, labelling them "disgusting", while those close to her told investigators she was a "good mother".
Throughout the hearing the emotional woman has sat at the back of the court alongside family members, stroking a stuffed toy wombat.
In her closing address, David said those who knew her client were "of the view that she didn't do it and was not capable" of deliberately infecting her son.
The woman's ex-husband said as much during his police interview on October 3, 2014, David said, telling officers she loved their son and would never hurt him.
David said the woman, now 39, had no idea what she was being accused of when first interviewed by Family and Community Services(FACS) and presented as someone who was "honest" and "open".
When police searched the woman's bags they found no syringes, nor samples of faeces, and she had no opportunity or reason to have discarded any evidence beforehand, the court heard.
She even raised the positive E coli test with child protection officers because she was concerned about her son's treatment, David said.
In one of three interviews with investigators, she claimed her child was being taken away "because of a friggin' doctor who's saying stuff that's not true".
"I think someone's stuffed up and it's poor old mum who gets the blame," she said.
David said the woman presented as a "person who one could believe, a person who was trying to do her best the whole way through and there would be no reason why you would not accept her denials".
"There's no reason to reject them. There's no other evidence," she said.
In the boy's interview, he asked for his mother several times and told officers "she wouldn't inject anything into me", the court heard.
"No, no one put anything in my cannula. Not the nurses, not my mum," he told police.
The boy said his brain had gone "all funny" when he accused his mother of poisoning him, with the court previously hearing he had been high on morphine at the time.
David said Isaacs pressed his theory of deliberate infection despite several alternatives, and FACS and police went along with it.
Other explanations included the blood sample being inadvertently contaminated when it was taken, lab contamination and also faecal matter being accidentally passed on by a visiting young relative.
"It is unjustified that this case could get to the position where we are in right now," David said.
"My submission is they got it wrong. There is no evidence to justify or support that the accused has committed this crime."
At the end of the hearing Judge Justin Smith reserved his judgment and will hand down a verdict on Tuesday next week.
- NCA NewsWire
