Intestinal microbiota changes due to Giardia intestinalis infections in a longitudinal Ecuadorian birth cohort and impact on cobalamin biosynthesis.

BackgroundGiardia intestinalis is a protozoal parasite infecting the gastrointestinal tract worldwide. Chronic infections/reinfections are common, with adverse nutritional consequences for critical growth during the first five years of life. Vitamin B12 (cobalamin) is absorbed primarily in the ileum of the small intestine, where Giardia trophozoites attach and replicate. Bacteria activate bioavailable vitamin B12, which is essential for human DNA synthesis and development. A disturbance in cobalamin biosynthesis caused by giardiasis may contribute to impairment of childhood development and growth. Methodology/Principal FindingsWe performed a longitudinal analysis on 61 Ecuadorian children using multi-parallel real-time quantitative PCR and whole genome sequencing. Children had increased Giardia DNA burden from ages 3 to 5 (p = 0.0012) and 7.58 times more frequent Giardia infections (1.31 to 34.33, P = 0.0176). There was an increased alpha diversity/ Giardia fg/{micro}l in three-year-olds compared to age-matched non-infected (30.20 vs 4.37, p = 0.050), but decreased alpha diversity/ Giardia fg/{micro}l in five-year-olds compared to age-matched non-infected children (0.21 vs 4.31, p = 0.021). Alpha diversity/ Giardia fg/{micro}l was also decreased in samples collected longitudinally from the same children at five compared to 3 years (p = 0.031). Cobalt transport protein (CbiN) (FDR < 0.003) and IPR011822 (Cobalamin-dependent methionine synthase) sequences were decreased in infected children (p < 0.002) and among those with greatest Giardia burdens (p < 0.001). Conclusion/SignificanceGiardia intestinalis infection may affect bacterial diversity in the ileum where vitamin B12 is activated, as suggested by a reduced proportion of Cobalt transport protein component (CbiN) gene sequences in the gut microbiome of infected children. These findings are potentially important to our understanding of how Giardia infections may affect childhood growth.