Surface characteristics of Escherichia coli strains in relation to development of bacteraemia

Three groups of E. coli bacteria isolated from blood, urine and faeces were analysed with respect to physicochemical surface properties in aqueous polymer two-phase systems. Eighty-eight per cent of the bacteria isolated from blood cultures showed affinity for the dextran-rich bottom phase, whereas 60% and 30% of the bacteria isolated from urine and faeces, respectively, collected to the same phase. Further two-phase analysis indicated that the bacteraemia strains exposed more negative surface than the other groups of bacteria, and that this charge was reduced after heat treatment (70 degrees C, 40 min). These results thus indicate that the strains causing bacteraemia possess similar surface properties, and may have been selected from the more heterogeneous group of bacteria found in urine and faeces. It is further conceivable to propose that bacteria found in the blood expose more heatsensitive, negatively-charged K antigen than the other groups of bacteria.