Expression of surface hydrophobicity encoded by R-plasmids in Escherichia coli laboratory strains.

The inclusion of drug-resistance plasmids (R-plasmids) in Escherichia coli strains has been shown to determine the formation of specific surface structures which could modify bacterial surface characteristics relevant for pathogenic processes. Thirtyone R-plasmids (from different incompatibility groups) have been transferred to three E. coli laboratory strains, and surface hydrophobicity modifications have been measured by three methods: "salting-out", adsorption to hexadecane and adsorption to xylene. The results obtained show that the presence of R-plasmids produced variations which are dependent on the receptor strains and measuring method employed. Also, it has been found that the plasmids behave differently depending on the strain in which they are included. The results obtained by the "salting-out" method are not correlative with those obtained by adsorption to hydrocarbons, probably due to the implication of different hydrophobic molecules in the interaction with salt or hydrocarbons. Concluding, the choice of receptor strain and measuring method are of great importance for the investigation of surface hydrophobicity (and probably other characteristics) encoded by R-plasmids.