Rapid change of fecal microbiome and disappearance of Clostridium difficile in a colonized infant after transition from breast milk to cow milk.

BACKGROUND: Clostridium difficile is the most common known cause of antibiotic-associated diarrhea. Upon the disturbance of gut microbiota by antibiotics, C. difficile establishes growth and releases toxins A and B, which cause tissue damage in the host. The symptoms of C. difficile infection disease range from mild diarrhea to pseudomembranous colitis and toxic megacolon. Interestingly, 10-50 % of infants are asymptomatic carriers of C. difficile. This longitudinal study of the C. difficile colonization in an infant revealed the dynamics of C. difficile presence in gut microbiota. METHODS: Fifty fecal samples, collected weekly between 5.5 and 17 months of age from a female infant who was an asymptomatic carrier of C. difficile, were analyzed by 16S rRNA gene sequencing. RESULTS: Colonization switching between toxigenic and non-toxigenic C. difficile strains as well as more than 100,000-fold fluctuations of C. difficile counts were observed. C. difficile toxins were detected during the testing period in some infant stool samples, but the infant never had diarrhea. Although fecal microbiota was stable during breast feeding, a dramatic and permanent change of microbiota composition was observed within 5 days of the transition from human milk to cow milk. A rapid decline and eventual disappearance of C. difficile coincided with weaning at 12.5 months. An increase in the relative abundance of Bacteroides spp., Blautia spp., Parabacteroides spp., Coprococcus spp., Ruminococcus spp., and Oscillospira spp. and a decrease of Bifidobacterium spp., Lactobacillus spp., Escherichia spp., and Clostridium spp. were observed during weaning. The change in microbiome composition was accompanied by a gradual increase of fecal pH from 5.5 to 7. CONCLUSIONS: The bacterial groups that are less abundant in early infancy, and that increase in relative abundance after weaning, likely are responsible for the expulsion of C. difficile.

The orphan response regulator EpsW is a substrate of the DifE kinase and it regulates exopolysaccharide in Myxococcus xanthus.

Here we attempted to identify the downstream target of the DifE histidine kinase in the regulation of exopolysaccharide (EPS) production in the Gram-negative bacterium Myxococcus xanthus. This bacterium is an important model system for the studies of Type IV pilus (T4P) because it is motile by social (S) motility which is powered by T4P retraction. EPS is critical for S motility because it is the preferred anchor for T4P retraction in this bacterium. Previous studies identified the Dif chemosensory pathway as crucial for the regulation of EPS production. However, the downstream target of the DifE kinase in this pathway was unknown. In this study, EpsW, an orphan and single-domain response regulator (RR), was identified as a potential DifE target first by bioinformatics. Subsequent experiments demonstrated that epsW is essential for EPS biosynthesis in vivo and that EpsW is directly phosphorylated by DifE in vitro. Targted mutagenesis of epsW suggests that EpsW is unlikely the terminal RR of the Dif pathway. We propose instead that EpsW is an intermediary in a multistep phosphorelay that regulates EPS in M. xanthus.