The source of a blood infection linked to the death of two babies may never be found, a health chief has admitted.

Dr Alan Mathers, chief of medicine, women's and children's services at NHS Greater Glasgow and Clyde (NHSGGC), said the infants had been amongst the "most vulnerable patients" in the country.

He said staff at the Princess Royal Maternity Hospital had been left "devastated" by the deaths, which were in part due to the Staphylococcus aureus blood stream infection.

Dr Mathers said: "The strain is one they have never seen before, it is possible the source will never be found."

He added: "Staff here perform miracles every day, this has left them devastated."

An incident management team (IMT) has been set up to investigate the blood stream infection found at the hospital's neonatal unit.

NHSGGC said in a statement that the two babies who died were "extremely poorly" due to their early births, with infection being "one of a number of contributing causes in both deaths".

A third baby is receiving treatment for the bacterium after the IMT was triggered on January 24.

Jason Leitch, clinical director of Healthcare Quality and Strategy, said: "This unit hasn't had an MRSA infection for 13 months.

"That's unbelievable if you think back ten years, five years even.

"But they've had three in this very short period of time so nobody is more concerned about that than the staff in that unit."

Meanwhile, First Minister Nicola Sturgeon expressed her "heartfelt and sincere condolences" to the parents.

During First Minister's Questions on Thursday, Sturgeon claimed that the local health board was "taking all necessary steps".

She said: "Staphylococcus aureus is, unfortunately, not an uncommon infection in people in hospital, including neonatal babies, and indeed that infection can be found in around one in four people.

"So, that makes it all the more important that hospitals have in place rigorous infection control procedures."

She added: "Our primary concern, and indeed that of the health board, is the safety and wellbeing of patients and their families at all time.

"The health board is taking all necessary steps to manage this incident and ensure patient safety."

Scottish Tories interim leader Jackson Carlaw MSP asked when ministers first became aware of the infection.

He said: "The investigation into this case was triggered last Thursday, January 24.

"Will the First Minister say when she and the Health Secretary were first made aware by the health board of these cases?"

Ms Sturgeon responded: "The Health Secretary became aware of these infections, I understand, on Monday of this week, and at that point asked for assurances."

She added that Jeane Freeman had been "in regular contact" with NHS Greater Glasgow and Clyde.

The babies' deaths come after two other deaths at Glasgow's Queen Elizabeth University Hospital, where a ten-year-old boy contracted the Cryptococcus infection.

Prosecutors are investigating the incident and also the death of a 73-year-old woman, which was initially said not to be related to the infection connected to pigeon droppings.

A staphylococcus infection or staph infection is an infection caused by members of the Staphylococcus genus of bacteria.

These bacteria commonly inhabit the skin and nose where they are innocuous, but may enter the body through cuts or abrasions which may be nearly invisible.

Once inside the body, the bacterium may spread to a number of body systems and organs, including the heart, where the toxins produced by the bacterium may cause cardiac arrest.

Once the bacterium has been identified as the cause of the illness, treatment is often in the form of antibiotics and, where possible, drainage of the infected area.

However, many strains of this bacterium have become resistant to the available regimens of antibiotics - for those suffering these kinds of infection, the body's own immune system is the only defence against the disease.

If that system is weakened or compromised, the disease may progress rapidly.