Genetic analysis of 987P adhesion and fimbriation of Escherichia coli: the fas genes link both phenotypes.

The 987P fimbrial gene cluster has recently been shown to contain eight genes (fasA to fasH) clustered on large plasmids of enterotoxigenic Escherichia coli and adjacent to a Tn1681-like transposon encoding the heat-stable enterotoxin STIa. Different genetic approaches were used to study the relationship between 987P fimbriation and adhesion. TnphoA mutagenesis, complementation assays, and T7 RNA polymerase-promoted gene expression indicated that all of the fas genes were involved in fimbrial expression and adhesion. In contrast to other fimbrial systems, the lack of expression of any single fas gene never resulted in the dissociation of fimbriation and adhesion, indicating that the adhesin is required for fimbrial expression and suggesting that FasA, the fimbrial structural subunit itself, is the adhesin. In addition, fimbrial length was shown to be modulated by the levels of expression of different fas genes.