In a statement, Aptamil - a Danone Nutricia business - said a batch of 67,000 units that included the product in question was "tested for bacteria before leaving our factory."
Laura Stevens from Swindon, Wiltshire, contacted Aptamil after her son, Ronan, spent a week in hospital with diarrhoea and a temperature caused by Campylobacter bacteria, the Bath Chronicle reported.
She insists that all Ronan was fed in the run up to his illness was Aptamil.
The Bath Chronicle added that Ronan's mother has since switched to SMA, infant formula manufactured by Nestlé.
“We are aware of this complaint and were concerned to hear that baby Ronan had been unwell," said Aptamil in a statement. "We are pleased that he is better now.”
"Extremely high standards"
None of the infant formula in question was left by the time Ronan's mother contacted Aptamil, it was reported.
Instead, she sent the Aptamil what was left of the packaging.
Unable to test the Aptamil fed to baby Ronan, the company looked back on its manufacturing records.
"We have already checked our records which show this batch had the all clear when it left our factory and there have been no other similar complaints," said Aptamil.
"We have controls and tests in place to ensure that our milks are made to extremely high standards."
"Our milks are pasteurised and heat treated to very high temperatures and laboratory tested for bacteria before leaving our factory," it said.
To date, Aptamil has not been approached by any British public health bodies, but says it "would be happy to help in any official investigation."
Food poisoning
Campylobacter is the most common cause of food poisoning in the UK, according to the Food Standards Agency (FSA).
Around four in five cases of Campylobacter poisoning in the UK can be traced back to contaminated poultry, it says.
Making this link, Aptamil said: "We do not have any poultry or meat ingredients in this product or at our factory."