Persistent gut barrier damage and commensal bacterial influx following eradication of Giardia infection in mice

Abstract

BackgroundRecent studies of Giardia lamblia outbreaks have indicated that 40–80% of infected patients experience long-lasting functional gastrointestinal disorders after parasitic clearance. Our aim was to assess changes in the intestinal barrier and spatial distribution of commensal bacteria in the post-clearance phase of Giardia infection.MethodsMice were orogastrically inoculated with G. lamblia trophozoites (strain GS/M) or pair-fed with saline and were sacrificed on post-infective (PI) days 7 (colonization phase) and 35 (post-clearance phase). Gut epithelial barrier function was assessed by Western blotting for occludin cleavage and luminal-to-serosal macromolecular permeability. Gut-associated, superficial adherent, and mucosal endocytosed bacteria were measured by agar culturing and were examined by fluorescence in situ hybridization. Intracellular bacteria cultured from isolated mucosal cells were characterized by 16S rDNA sequencing. Neutrophil-specific esterase staining, a myeloperoxidase activity assay, and enzyme-linked immunosorbent assays for cytokine concentrations were used to verify intestinal tissue inflammation.ResultsTight junctional damage was detected in the intestinal mucosa of Giardia-infected mice on PI days 7 and 35. Although intestinal bacterial overgrowth was evident only during parasite colonization (PI day 7), enhanced mucosal adherence and endocytosis of bacteria were observed on PI days 7 and 35. Multiple bacterial strains, including Bacillus, Lactobacillus, Staphylococcus, and Phenylobacterium, penetrated the gut mucosa in the post-infective phase. The mucosal influx of bacteria coincided with increases in neutrophil infiltration and myeloperoxidase activity on PI days 7 and 35. Elevated intestinal IFNγ, TNFα, and IL-1β levels also were detected on PI day 35.ConclusionsGiardia-infected mice showed persistent tight junctional damage and bacterial penetration, accompanied by mucosal inflammation, after parasite clearance. These novel findings suggest that the host’s unresolved immune reactions toward its own microbiota, due to an impaired epithelial barrier, may partly contribute to the development of post-infective gut disorders.

The Intersection of Immune Responses, Microbiota, and Pathogenesis in Giardiasis

“…Additionally, Giardia exposure may lead to increased prevalence of perceived food intolerance in humans [10], although the cause for this reaction was not identified. The concept of food antigen translocation is supported by various reports of increased intestinal epithelial barrier permeability during infection [5, 11–14]. The Global Enteric Multicenter Study (GEMS) reported that Giardia infections appear to reduce the incidence of severe diarrheal disease in children in the developing world [15].…”

“…In contrast, a cathepsin B-like cysteine protease secreted by Giardia can modulate immune responses by degrading CXCL8, a neutrophil attractant [48]. In addition to reducing NO production, consumption of arginine by Giardia was shown to reduce IEC proliferation [44], and infection reduced intestinal epithelial barrier function [11, 12, 14, 49]. It is reasonable to assume that this disruption is partly mediated by Giardia proteins and enzymes through excretory/secretory pathways [50].…”

Gut microbiota related to Giardia duodenalis, Entamoeba spp. and Blastocystis hominis infections in humans from Côte d’Ivoire

“…It is now well known that these protozoa are constantly interacting with the intestinal microbiota, but their possible relation to imbalances in microbiota composition, termed dysbiosis, is still unclear. Giardia infection may trigger long-lasting changes in the spatial distribution of commensal microorganisms, enhancing bacterial invasiveness and inflammatory responses in the gut mucosa during the post-clearance phase [9]. Regarding E. histolytica, significant alterations of predominant gut bacteria and a depletion of some predominant genera (e.g., Bacteroides, Eubacterium, Lactobacillus) in the gut of infected patients has been described [10].…”

Giardia Alters Commensal Microbial Diversity throughout the Murine Gut

“…Cultures of jejunal juice from patients with active giardiasis revealed increased total bacterial load, increased abundance of Enterobacteriacae, and perturbed bile acid homeostasis (27,28). Giardia infection also causes increased bacterial loads midinfection and increased bacterial invasiveness postclearance as a sequela to intestinal barrier disruption (29).…”