Encouraging a mother to spit on her baby may not sound like good science, but it is the basis of a world-first study in New Zealand.

The University of Otago study aims to determine if newborns can receive, and establish, good bacteria that have been introduced to their mother's mouths.

Pregnant women will suck a probiotic lozenge each day of the last month of their pregnancy to colonise their mouths with the bacteria associated with preventing sore throats and ear infections.

"There has been no study like this before," Professor John Tagg said.

Women would be checked to see if they naturally carried streptococcus salivarius K12, which occurs naturally in 5 per cent of the population.

Why some people had K12 was a mystery; it was random, but there were indications it ran in families.

"What we want is to take the randomness out of it," he said.

If his theory is right, his method will establish the good bacteria, potentially with life-long benefits.

"When she kisses baby, it should give the kiss of protection to her baby."

The study is based on the same principle as Blis K12 Throat Guard, which Professor Tagg developed.

Only two participants were signed up for the trial, but Professor Tagg hoped about 50 women would take part over the next year.

Sterile when they were born, babies inherited bacteria from their main carer, usually their mother.

The person who got the most "spits in" passed on their bacteria to the baby. Babies would be checked for K12 at one week, and then at six weeks, to see if the bacteria remained.

The babies would not be tracked as they grew up, but that could be the basis of future research, Professor Tagg said.

Dunedin mother-of-three Anna Wescombe, who is six-and-a-half months pregnant, was pleased to be taking part in the study.

Hopefully her baby would benefit from the "good bacteria", Mrs Wescombe said.