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The P fimbrial gene clusters encoding the serologically different F71, F72, F9, and Fll fimbriae were compared functionally. The results show that these gene clusters are closely related.

Transformation of uropathogenic Escherichia coli strains with plasmid DNA was in general unsuccessful or very inefficient. Transformation was much more efficient when galE mutants of such strains, in which the lipopolysaccharide chains appeared shorter, were used as recipients.In studies on structures and functions involved in the virulence of pathogenic Escherichia coli strains, molecular cloning and in vitro DNA manipulations of relevant genomic regions are successful approaches (1,4,7,13,14,17). In such studies, transfer of cloned or manipulated genes to the pathogenic E. coli strains might be an essential step. Transformation is an obvious technique to accomplish this. For E. coli K-12, several transformation techniques, based on a Ca21 plus heat shock treatment of cells, have been reported (2,5,9,12).These techniques have been used to transform a number of uropathogenic E. coli strains belonging to various serological classes with the vector plasmids pBR322 and pA-CYC184. The procedure of Dagert and Ehrlich (5) reproducibly gave the best results. This technique was used in further experiments. The results of the transformation of a number of uropathogenic strains with pBR322 DNA are shown in Table 1. Strains AD110, AD119, and Z094 gave very low numbers of transformants. The low efficiency obtained with these strains is representative for most uropathogenic and wild-type E. coli strains isolated from sewage that we tested (a total of 15 were tested). Strain AD403 was rather exceptional since it appeared to be readily transformable. Similar results were obtained when plasmid pACYC184 was used (data not shown). The low efficiency that we observed in plasmid transformation with most of our wild-type E. coli strains could be the result of low DNA uptake, of DNA restriction, of incompatibility between the plasmid and resident plasmids, or of a combination of any of these factors. Incompatibility is unlikely to be the main cause for the low efficiency, since we obtained comparably low yields with pBR322 and with pACYC184, plasmids that belong to different incompatibility groups. The low transformability is more likely caused by inefficient DNA uptake and by restriction.In E. coli transformation, DNA uptake appears to occur when the physical state of the membrane lipids changes from the solid to the liquid phase during the heat shock applied in the transformation protocols (16). Probably it is a prerequisite that the transforming DNA is in intimate contact with the recipient cell envelope during this short period, as discussed recently (6). The long lipopolysaccharide (LPS) chains present on the surface of most wild-type E. coli strains might prevent this contact. It has indeed been reported (3) that rough variants of smooth Salmonella typhimurium organisms, especially galE mutants, showed increased transfectability compared with their smooth parental strains.We therefore decide to isolate galE mutants of the three uropathogenic strains (Table 1) that showed low transforma-* Corresponding author. 760 bility. The E. ...

E. coli K12 transformants, selected as leu+ or pyrA+ transformants, were analysed for inheritance of some closely linked unselected markers. Based on the observation that the number of recombinants which require, besides an integration event, one or more crossing-over events was negligible, a simple mapping function was deduced. The function L= e-kd, which directly relates observed linkage of an unselected marker and the relative distance of that unselected marker to the selected marker, gave a consistent interpretation of the experimental results.