Evaluation of numerical analysis of SDS-PAGE of protein patterns for typing Enterobacter cloacae

Twenty cultures comprising 13 clinical isolates of Enterobacter cloacae from two hospitals, the type and another reference stain of E. cloacae and the type strains of four other Enterobacter sp. and of Escherichia coli, were characterized by one-dimensional sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) of whole-cell proteins. The protein patterns were highly reproducible and were used as the basis of a numerical analysis which divided the clinical isolates into nine clearly defined protein types. Comparison with established typing methods indicated that the discrimination of SDS-PAGE was similar to that achieved with conventional typing methods and all strain groups recognized by combined sero/phage typing were also found by SDS-PAGE. In addition, protein typing sub-divided a group of four serotype O3 isolates that were difficult to distinguish by phage typing. We conclude that high-resolution SDS-PAGE of proteins provides an effective method of typing isolates of E. cloacae.