Partition of Escherichia coli in an aqueous polymer two-phase system

Abstract The partition of various strains of Escherichia coli in a two-phase system containing 5 per cent (w/w) dextran and 4 per cent (w/w) polyethylene glycol has been studied. Strains grown in a broth medium or on the surface of agar had a reproducible partition behaviour which was more or less strongly influenced by the presence of NaCl in the phase system. Repeated washings of the cells, heating to a lethal temperature or treatment with detergents or formaldehyde did not change their phase affinity. The source of carbon for growth had a marked effect on the phase affinity of some strains. Cells grown in broth or a defined medium with glucose normally partitioned into the bottom phase in the presence of NaCl whereas succinate grown cells partitioned into the top phase under similar conditions. Some strains of defined serotype could be distinguished on the basis of their partition behaviour. Loss of flagellar antigens had little effect on the phase affinity whereas changes in capsular antigens usually resulted in marked changes in partition behaviour. The phase affinity of one strain was influenced by reaction between the cells and a type specific antiserum whereas other strains were less sensitive to a similar treatment.