Intestinal bacterial colonisation in pre-term infants is delayed compared with 
full-term infants, leading to an increased risk of gastrointestinal disease. 
Modulation of colonisation through dietary supplementation with probiotics or 
prebiotics could decrease such a risk. The present study evaluated clinical 
tolerance, the effects on gut microbiota, and inflammatory and immunological 
mucosal responses to an infant formula adapted for pre-term infants that 
included in its manufacturing process a fermentation step with two probiotic 
strains, Bifidobacterium breve C50 and Streptococcus thermophilus 065, 
inactivated by heat at the end of the process. A total of fifty-eight infants 
(gestational age: 30-35 weeks), fed either the fermented pre-term formula or a 
standard pre-term formula, were followed up during their hospital stay. Clinical 
tolerance, faecal microbiota using a culture and a culture-independent method 
(temporal temperature gel electrophoresis), faecal calprotectin and secretory 
IgA were analysed weekly. No difference was observed regarding anthropometric 
data and digestive tolerance, except for abdominal distension, the incidence of 
which was lower in infants fed the fermented formula for 2 weeks. Bacterial 
colonisation was not modified by the type of feeding, particularly for 
bifidobacteria. Faecal calprotectin was significantly lower in infants fed the 
fermented formula for 2 weeks, and secretory IgA increased with both mother's 
milk and the fermented formula. The fermented formula was well tolerated and did 
not significantly modulate the bacterial colonisation but had benefits on 
inflammatory and immune markers, which might be related to some features of 
gastrointestinal tolerance.