Abstract
It is possible to differentiate isolates of Escherichia coli using a number of techniques including the determination of the serotype, biotype and phage type and the profiles for resistance to antibacterial agents and toxic chemicals, intracellular enzymes, outer membrane proteins and plasmids and the production of enterotoxin and colicines. These methods have been used principally for the study of pathogenic E. coli and plasmid-mediated drug resistance. However they can also be used successfully for ecological purposes and the application of several of these techniques for the study of the ecology of E. coli in healthy young animals including man is described.