Salt aggregation test for measuring cell surface hydrophobicity of urinary Escherichia coli

The recently developed salt aggregation test for measuring relative surface hydrophobicity of bacteria was used to study Escherichia coli strains isolated from urinary tract infections. Of the 232 strains tested 166 (71.5%) aggregated in salt solutions of varying molarity (0.1-1.6 M final concentration). Mannose-resistant haemagglutination of various erythrocyte species and/or mannose-sensitive haemagglutination of guinea-pig erythrocytes was seen in 144 of the 166 salt aggregating strains. Two salt aggregation-negative (hydrophilic) strains exhibited mannose-sensitive haemagglutination. Fimbriae of varying morphology were seen in salt aggregating strains. Strains with type 1 fimbriae only generally showed lower surface hydrophobicity than strains exhibiting mannose-resistant haemagglutination. Growing strains at 18 degrees C suppressed fimbriation with a concomitant decrease in surface hydrophobicity and haemagglutination. The salt aggregation test proved to be a rapid and reproducible screening test for detecting bacteria with high surface hydrophobicity due to surface protein of fimbrial (haemagglutinating or non-haemagglunating) and non-fimbrial nature.