The biotyping of Escherichia coli isolated from healthy farm animals.

A total of 2973 Escherichia coli, isolated from six different groups of animals, were examined for their ability to ferment adonitol, dulcitol, raffinose, rhamnose and sorbose in solid media. Twenty-nine fermentation patterns were recorded although 2443 (82%) of the E. coli belonged to seven of the 32 possible biotypes. Ninety-six O-serotypes were identified within the 2973 E. coli. The number of O-serotypes represented in the 15 most common biotypes ranged from three to 15. Serotypes O8 and O9 were found most commonly in the different groups of animals and several biotypes amongst these two O-serotypes were identified in two or more groups of the animals. The ability of the E. coli to metabolize aesculin, ornithine, salicin and sucrose was also assessed. These test proved less reproducible and were not included in the primary biotyping scheme although their use allowed the enumeration of additional biotypes. The application of biotyping to the study of the ecology of drug-resistant strains of E. coli in five situations is briefly presented.