INTRODUCTION Escherichia coli is a well known Gram negative bacterium which principle habitats in the colon. Most strains of E. coli are harmless saprophytes and nonpathogenic. Other strains which cause diseases such as enteric infections, septicemia, urinary infection and mastitis, are identified their pathogenicities by several systems such as serotyping, biotyping, phage-typing, electrophoretic-typing, colicin-typing and testing for virulence factors (Gyles, 1993). The differentiation of pathogenic strains from non-pathogenic strains, which are normal gut flora, can be demonstrated to identify their virulence factors.