The purpose of this study is:

• to study the intestinal microflora of colicky infants before and after L. reuteri or placebo administration, evaluating the effect of Lactobacillus reuteri on the growth of the main intestinal microbiota (coliforms, Clostridium butyricum, Lactobacilli, Bifidobacteria) with fluorescent in situ hybridization (FISH) technique or with Real-Time PCR Taqman; Further, the global intestinal microflora composition, using large-scale DNA sequencing of 16S rRNA genes ( 454-pyrosequencing technique.
• to evaluate the improvement of colicky symptoms by the oral administration of Lactobacillus reuteri (primary outcome: reduction of the daily average crying time from baseline to the end of the treatment period, to less than 3 hours a day, the cut-off proposed by Wessel; secondary outcome: number of responders versus non-responders in each group at the end of the treatment).
• to evaluate fecal calprotectin values at the beginning and at the end of the study. BÜHLMANN Quantum Blue® Calprotectin High Range (Schönenbuch, Switzerland). A quantitative immunoassay.
• to evaluate Th17/Treg balance at time 0 and t 30 ( days) investigating mRNA FOXP3 and RORγ in peripheral blood using RT-PCR Real Time Taqman.
• the measurement of the expression level of CC-chemokine receptor 7 messenger RNA using the real-time TaqMan reverse transcription polymerase chain reaction method.
• the measurement of expression of interleukin 10 (IL-10) messenger RNA using the real-time TaqMan reverse transcription polymerase chain reaction method.
• Parental satisfaction at the end of the study period ( 30 day ) with a numerc scale from 1 to 10.

Infantile colic is one of the most common problems within the first three months of life. It consists of a behavioural syndrome characterised by paroxysmal, excessive and inconsolable crying without identifiable cause. Although infantile colic is commonly reported and causes appreciable distress for both parents and paediatricians, despite forty years of research, its aetiology still remains unclear. Recently the role of intestinal microflora has growing importance, and a lower count of intestinal lactobacilli has been observed in colicky infants compared to healthy ones. In a recent study we have observed that Lactobacillus reuteri improved colicky symptoms in breast-fed infants within one week of treatment compared to Simethicone, suggesting that probiotics may play a role in infantile colic (Savino F, Pelle E, Palumeri E, Oggero R, Miniero R.Lactobacillus reuteri (American Type Culture Collection Strain 55730) versus simethicone in the treatment of infantile colic: a prospective randomized study. Pediatrics 2007; 119:e124-30). The mechanism involved in such finding is only partially understood and, for this reason, we have planned this new study to evaluate not only the clinical improvement but also the microbiological data.

Inclusion Criteria:

• clinical diagnosis of infantile colic according to Wessel's criteria
• gestational age between 37 and 42 weeks
• age between 4 and 16 weeks
• birth weight between 2500 and 4000 g
• exclusively breastfed

Exclusion Criteria:

• clinical evidence of chronic illness or gastrointestinal disorders
• administration of probiotics and antibiotics

to partecipe to an individual partecipant data meta- analysis.