Colonization and distribution of segmented filamentous bacteria (SFB) in chicken gastrointestinal tract and their relationship with host immunity.

Uncultivable segmented filamentous bacteria (SFB) reside in the gastrointestinal (GI) tract of mammals and can boost the host immunity. Immunoglobulin A (IgA) from mother's milk has been previously shown to be a key factor in regulating SFB colonization. Because neonatal chicken cannot acquire IgA from maternal milk, they are a good model to examine the role of IgA in SFB colonization. Here, we used the fluorescent in situ hybridization (FISH) and quantitative PCR (qPCR) to monitor the colonization and distribution of SFB in chickens aged from 2-day-old to 6-week-old. Early SFB colonization, which primarily occurred in the ileal mucosa (< 13 days old), was IgA independent. From the age of 17-42 days, there was an increase in IgA in the gut mucosa, which was correlated with a decrease in SFB. To examine the effect of probiotics and immunosuppression on SFB colonization, we treated the chickens by feeding them Lactobacillus delbrueckii or giving them a subcutaneous injection of cyclophosphamide (CTX). Feeding lactobacilli at birth rendered SFB colonization occurring 4 days earlier, while CTX treatment increases the SFB colonization through reducing the other non-SFB bacteria. Altogether, our data suggest that early colonization of SFB in chicken occurs independently of IgA and the population of SFB in the GI tract of chicken may be manipulated from birth via probiotic or CTX treatment.