Celiac disease (CD) is an immune-mediated enteropathy involving genetic and environmental factors whose interaction might influence disease risk. The aim of this study was to determine the effects of milk-feeding practices and the HLA-DQ genotype on intestinal colonization of
Bacteroidesspecies in infants at risk of CD development. This study included 75 full-term newborns with at least one first-degree relative suffering from CD. Infants were classified according to milk-feeding practice (breast-feeding or formula feeding) and HLA-DQ genotype (high or low genetic risk). Stools were analyzed at 7 days, 1 month, and 4 months by PCR and denaturing gradient gel electrophoresis (DGGE). The Bacteroidesspecies diversity index was higher in formula-fed infants than in breast-fed infants. Breast-fed infants showed a higher prevalence of Bacteroides uniformisat 1 and 4 months of age, while formula-fed infants had a higher prevalence of B. intestinalisat all sampling times, of B. caccaeat 7 days and 4 months, and of B. plebeiusat 4 months. Infants with high genetic risk showed a higher prevalence of B. vulgatus, while those with low genetic risk showed a higher prevalence of B. ovatus, B. plebeius, and B. uniformis. Among breast-fed infants, the prevalence of B. uniformiswas higher in those with low genetic risk than in those with high genetic risk. Among formula-fed infants, the prevalence of B. ovatusand B. plebeiuswas increased in those with low genetic risk, while the prevalence of B. vulgatuswas higher in those with high genetic risk. The results indicate that both the type of milk feeding and the HLA-DQ genotype influence the colonization process of Bacteroidesspecies, and possibly the disease risk.