Influence of bacteria from the duodenal microbiota of patients with symptomatic giardiasis on the pathogenicity of Giardia duodenalis in gnotoxenic mice

Recent studies have shown that the intestinal microbiota is essential for t he pathogenicity but not for the multiplication of Giavdia duodenalis in th e intestinal lumen. The microbial components responsible for this phenomeno n are not known. Twenty-eight facultative and three strictly anaerobic micr o-organisms were isolated from the dominant duodenal microbiota of five pat ients with symptomatic giardiasis, The bacterial combinations from each pat ient were associated with groups (GN) of germ-free mice. Five days after th e association, when their faecal populations ranged from 10(7) to 10(9) cfu /g, all groups were inoculated intragastrically with 10(5) viable trophozoi tes of G, duodenalis strain BT6, Two groups of germ-free (GF) and conventio nal (CV1) mice were also infected. Gnotobiotic animals were killed 10 days after infection and GF and CV1 animals were killed 10, 20 and 30 days after infection, More marked pathological alterations were detected in CV1 mice when compared with GF animals. Gnotobiotic animals showed intermediate path ological alterations between CV1 and GF mice. The CV1 and GF groups became infected by day 3 and faecal cyst levels were similar in both groups throug hout the experiment. Total and G, duodenalis-specific IgA levels in the int estinal fluid and G, duodenalis-specific IgM and IgG levels in the serum in creased during the infection and were higher in CV1 animals at all times te sted when compared with GF mice. The present results confirm the stimulator y activity of the intestinal microbiota on the pathogenicity of G, duodenal is, and some combinations of microbial components of the dominant duodenal ecosystem from patients with symptomatic giardiasis can partially develop t his function, However, none of these combinations was able to stimulate the protozoan pathogenicity in the same manner as the entire intestinal microb iota.