The gastrointestinal microbiota of preterm infants in neonatal intensive care units (NICU) differs from that of term infants, which may be attributable to the use of parenteral nutrition and antibiotic therapy for extended periods. In addition, colonization by bifidobacteria as occurring in normal term infants can be delayed in this population. The NICU environment predisposes these infants to nosocomial infections, and probiotics may help to reduce the infection by decreasing the overgrowth of pathogenic bacteria. A double-blind, placebo controlled randomized clinical study was performed on 69 preterm infants (Probiotic and Placebo groups; 37 and 32 infants, respectively) to investigate the role of Bifidobacterium lactis Bb12 in modifying the gut microbiota and in providing an improved health status.
Various methods were used to monitor the influence of probiotic supplementation. Both culture dependent (culturing of the faecal sample on selective and non-selective media) and culture independent approaches (flourescene in situ hybridization and denaturing gradient gel electrophoresis) were used to study the establishment and modification of the gut microbiota. Calprotection levels were monitored as an indicator of inflammation and disease. In addition, faecal short chain fatty acids and lactate were measured as biochemical markers to get an insight into the bacterial fermentation in the colon. Total faecal IgA was also measured for some infants as its levels have been shown to be higher after Bb12 supplementation. For ethical reasons, all parameters chosen for the study were non-invasive.
B. lactis Bb12 was well tolerated by all infants in the probiotic group. One of the most important outcomes of the study was the improved weight gain in the infants who received the probiotic preparation (1924 g ± S.D. 331) as compared to the ones in the placebo group (1811 g ± 326). Mean log10 values of bifidobacterial numbers per gram wet weight faeces estimated with fluorescence in situ hybridization were significantly higher in the probiotic group (Probiotic = 8.18 + S.E.M.0.54; Placebo = 4.82 + 0.51; p < 0.001). Mean log10 values of colony forming units per gram wet weight faeces were significantly reduced by B. lactis Bb12 supplementation in the case of Enterobacteriaceae (Probiotic = 7.80 + 0.34; Placebo = 9.03 + 0.35; p = 0.015) and Clostridium spp. (Probiotic = 4.89 + 0.30; Placebo = 5.99 + 0.32; p = 0.014). The faecal pH in the probiotic group (5.68 + 0.009) was significantly lower as compared to the placebo group (6.38 + 0.010; p < 0.001) which was probably due to 42% higher faecal acetate and 38% higher faecal lactate in the probiotic group. Low pH facilitates the proliferation of lactic acid bacteria and bifidobacteria and inhibits the growth of pathogenic microorganisms. Faecal calprotectin, a non-invasive marker for inflammation, was significantly lower (p = 0.041) in the probiotic group (269.77 mg/kg + 26.71) than in the placebo group (350 mg/kg + 31.19). Faecal IgA, which plays a central role in local immunity and has a significant function in creating a barrier against infections by pathogenic bacteria or viruses, was significantly higher in the probiotic group as compared to the placebo group (Probiotic = 4.40 mg/kg + 0.49; Placebo = 2.47 mg/kg + 0.59; p = 0.021).
The present study indicates that the supplementation of preterm infants with B. lactis Bb12 supports a better weight gain and improves a number of health parameters.
It was not possible to draw any conclusion for the effect of B. lactis Bb12 supplementation in the prevention of necrotizing enterocolitis and bacterial sepsis due to the small number of NEC and sepsis cases in the study population although the present study does show the beneficial effects of B. lactis Bb12 supplementation in improving the general condition of preterm infants.