The aetiology of colic, a functional gastrointestinal disorder in infants, is not yet resolved. Different mechanisms have been suggested involving the gut microbiota and intermediate metabolites such as lactate. Lactate can be metabolized by lactate-utilizing bacteria (LUB) to form different end-products. Using a functional approach, we hypothesized that H2 production and accumulation by LUB is associated with the development of colic. The LUB communities in the feces of forty infants, including eight colicky infants, were characterized using a combination of culture- and molecular-based methods, and metabolite concentrations were measured by HPLC. Interactions among LUB strains isolated from feces were investigated with pure and mixed cultures using anaerobic techniques. We emphasized high prevalence of crying, flatulence, colic and positive correlations thereof in the first 3 months of life. Crying infants showed significantly higher ratio of LUB non-sulfate-reducing bacteria (LUB non-SRB) (H2-producer), to LUB SRB (H2-utilizer) at 3 months. Colicky infants had significantly higher number of H2-producing Eubacterium hallii at 2 weeks compared to non-colicky infants. We revealed the function of Desulfovibrio piger and Eubacterium limosum to reduce H2 accumulation in co-cultures with H2-producing Veillonella ratti. Our data suggest that the balance between H2-producing and H2-utilizing LUB might contribute to colic symptoms.