Bacteria that live in the nose and throat could be key to warding off childhood infections, say researchers.
Scientists have found that babies prone to colds and chest infections have variations in the bacteria that live in their respiratory tracts compared with healthy children.
The study, by researchers at the University of Edinburgh in collaboration with institutes in The Netherlands, could help determine how doctors boost protective bacteria to prevent infections in infants.
Acute respiratory infections account for 15% of all childhood deaths in under-fives worldwide, with one fifth of children developing a severe or recurrent infection.
The study focused on bacteria that are fundamental to maintaining health with many types colonising areas such as the upper respiratory tract, including the nose and throat.
Professor Debby Bogaert, of the University of Edinburgh's medical research council centre for inflammation research, said: "Our study paints the clearest picture yet of the make-up of infants' respiratory bacteria in their first year.
"Our findings suggest that there could be protective bacteria missing in some babies, affected by factors such as mode of delivery and infant feeding."
Researchers monitored the health of 112 babies throughout their first year, recorded all respiratory infections and characterised the babies' bacterial colonies.
Infants who contracted more infections had a different bacterial profile including variations in numbers and types compared to those who were more resistant.
Differences were apparent from as early as two weeks after birth, before the first infections occurred.
Environmental factors, such as breastfeeding, baby delivery method, having siblings and attending day care, were also found to affect the bacteria present.
Scientists say pinpointing the bacteria that are responsible for protection against infection holds the key to efforts to prevent infection in the future.
Prof Bogaert added: "The study really opens opportunities to explore how we could enhance these specific bacteria to help vulnerable babies ward off infection."
The findings are published in the American Journal of Respiratory and Critical Care Medicine and the study was supported by Dutch funding bodies.