The importance of P and type 1 fimbriae for the persistence of Escherichia coli in the human gut.

The faecal Escherichia coli flora was studied in 89 infants. Each infant was followed with a mean of 12 faecal samples (range 5-21) between 0 and 18 months of age. All isolates were assayed for P fimbriae and biochemically phenotyped and the persistence of each strain (phenotype) in the infant's gut was determined. In a subset of strains the occurrence of type 1 fimbriae and adherence to HeLa cells was studied. Thirty-one per cent of isolates belonging to strains colonizing for longer than 6 months expressed P fimbriae compared to 19% of the isolates from strains colonizing 1-6 months or transient strains colonizing less than 1 month. Type 1 fimbriae and adherence to HeLa cells occurred similarly often in all groups of strains. We conclude that P fimbriae, but not type 1 fimbriae or HeLa cell adherence seemed to contribute to the ability of the E. coli strain to colonize the human intestine.