A concise biotyping system for differentiating strains of Escherichia coli

A six test biotyping system comprising fermentation of dulcitol, sorbose, raffinose, and 5 ketogluconate, motility and production of beta-haemolysis was used to obtain biotype profiles for 514 strains of Escherichia coli isolated from the urinary tract. This profile was suffixed to the API-20E code, recorded when the strains were originally identified. An expanded and reliable biotyping system was thus created giving a greater number of possible biotypes than with either system alone. The sensitivity in terms of distinguishing the organisms studied was therefore greatly increased. The use of O-serotyping in combination with biotyping is discussed. Biotyping can also be usefully supplemented by the determination of the eight commonest E coli O-serotypes. This is of value in many clinical situations where differentiation of organisms is vital to the proper analysis of results.