Infants can be colonized by toxin producing strains of Clostridium difficile but rarely develop disease. Infants and children could play a source in the spread of C. difficile disease to adults.
Toxin-producing Clostridium difficile strains as long-term gut colonizers of healthy infants
Clostridium difficile is a colonizer of the human gut, and toxin-producing strains may cause diarrhea if infectious burden is heavy. Infants are more frequently colonized than adults, but rarely develop C. difficile disease. It is not known whether strains of C. difficile differ in capacity to colonize and persist in the human gut microbiota. Here, we strain-typed isolates of C. difficile colonizing 42 healthy infants followed from birth to ≥12 months of age, using PCR ribotyping of the 16S-23S rRNA intergenic spacer region. The isolates were also characterized regarding carriage of the toxin genes tcdA, tcdB and cdtA/B, and capacity to produce toxin B in vitro. Most strains (71%) were toxin-producers, and 51% belonged to the 001 or 014 ribotypes, that often cause disease in adults. These ribotypes were significantly more likely than other ones to persist for ≥6 months in the infant micobiota, and were isolated from 13/15 children carrying such long-term colonizing strains. Ribotype 001 strains were often acquired in the first week of life and attained higher population counts than other C. difficile ribotypes in newborn infants’ faeces. Several toxin-negative ribotypes were identified, two of which (GI and GIII) were long-term colonizers, each in one infant. Our results suggest that the toxin-producing C. difficile ribotypes 001 and 014 have special fitness in the infantile gut microbiota. Toxin-producing strains colonizing young children for long time periods may represent a reservoir for strains causing disease in adults.