Giardia Antagonizes Beneficial Functions of Indigenous and Therapeutic Intestinal Bacteria during Malnutrition

Abstract

ABSTRACTUndernutrition in children commonly disrupts the structure and function of the small intestinal microbial community, leading to enteropathies, compromised metabolic health, and impaired growth and development. The mechanisms by which diet and microbes mediate the balance between commensal and pathogenic intestinal flora remain elusive. In a murine model of undernutrition, we investigated the direct interactionsGiardia lamblia,a prevalent small intestinal pathogen, on indigenous microbiota and specifically on Lactobacillus strains known for their mucosal and growth homeostatic properties. Our research reveals thatGiardiacolonization shifts the balance of lactic acid bacteria, causing a relative decrease inLactobacillus spp. and an increase inBifidobacterium spp. This alteration corresponds with a decrease in multiple indicators of mucosal and nutritional homeostasis. Additionally, protein-deficient conditions coupled withGiardiainfection exacerbate the rise of primary bile acids and susceptibility to bile acid-induced intestinal barrier damage. In epithelial cell monolayers,Lactobacillus spp. mitigated bile acid-induced permeability, showing strain-dependent protective effects.In vivo, L. plantarum,either alone or within aLactobacillusspp consortium, facilitated growth in protein-deficient mice, an effect attenuated byGiardia, despite not inhibiting Lactobacillus colonization. These results highlight Giardia’s potential role as a disruptor of probiotic functional activity, underscoring the imperative for further research into the complex interactions between parasites and bacteria under conditions of nutritional deficiency.