Escherichia coli H10407 demonstrated low '25I-human lactoferrin (IlLf) binding (7%) and was insusceptible to group A (A, El, E2, E3, E6, and K) and group B (B, D, Ta, Ib, and V) colicins. Conversely, a spontaneous HLf high-binding (44%) variant, H10407(Lf), demonstrated an increased susceptibility to both colicin groups.Colicin-insusceptible E. coli wild-type strains 75ColT, 84ColT, and 98lColT showed a low degree of HLf binding, i.e., 4, 8, and 10%, respectively. The HLf binding capacity was high in the corresponding colicin-susceptible mutants 75ColS (43%), 84ColS (32%), and 981ColS (43%). Furthermore, HLf low-(<5%) and high-(>35%) binding E. coli clinical isolates (10 in each category) were tested for susceptibility against 11 colicins. Colicin V susceptibility did not correlate with HLf binding in either categories. However, with the remaining colicins, three distinct HLf-binding, colicin susceptibility patterns were observed; (i) 10 of 10 HLf low-binding strains were colicin insusceptible, (ii) 6 of 10 HLf high-binding strains were also colicin insusceptible, and (iii) the remaining HLf high binders were highly colicin susceptible. Certain proteins in the cell envelope and outer membrane of wild-type H10407 (HLf low binder, colicin insusceptible) showed a lower mobility in sodium dodecyl sulfate-polyacrylamide gel electrophoresis compared to the corresponding proteins of mutant H10407(Lf) (HLf high binder, colicin susceptible). These mobility differences were also associated with HLf-binding proteins in Western blot (ligand blot) analysis. The wild type showed a smooth form of lipopolysaccharide (LPS) with a distinct ladder of 0-chains, compared to the rough LPS of the mutant.Exogenous smooth LPS from wild-type H10407 inhibited 125T-HLf binding to mutant H10407(Lf) in a dose-dependent manner, while rough LPS was ineffective. These data establish a correlation between HLf binding and colicin susceptibility in E. coli. The LPS seems to be associated with the HLf binding components and the colicin receptors in a similar manner and interferes with the interaction of these eucaryotic and procaryotic antimicrobial agents with E. coli.

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The effect of 20 colicins and cloacin was studied after various precultivations. Nutrient agar supplemented with subinhibitory concentration of EDTA used for precultivation or elevating the growth-temperature of the inoculum from 37 degrees C to 42 degrees C increased the susceptibility of wild-type (smooth) Escherichia coli strains to the inhibitory action of some colicins. There were great differences among the colicins in respect to these effects. In case of rough mutants, their sensitivities did not change or eventually decrease after EDTA or heat pretreatment. The LPS pattern in SDS-PAGE of smooth cells grown in EDTA-containing nutrient medium changed in some degree towards the rough character. In case of precultivation at 42 degrees C this change was less considerable. It is supposed that both factors applied during precultivation have influence on colicin sensitivity by means of the change of receptor activity caused by LPS modification.

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