Use of multiple primers in RAPD analysis of clonal organisms provides limited improvement in discrimination

Randomly amplified polymorphic DNA (RAPD) analysis using two or more primer s has been reported to provide additional discriminatory ability over one p rimer used individually. This may be of particular application in epidemiol ogical typing of clonal organisms, such as Shiga toxin-producing E. coli O1 57, where strain differentiation can be difficult. Using four arbitrary pri mers individually, and in all possible permutations, E. coli O157 isolates and other arbitrarily chosen E. coli strains were typed using RAPD analysis . For most nonclonal strains, the use of two two primers resulted in increa sed differentiation between isolates; however more than two primers did not increase further the discriminatory capacity. E. coli O157 isolates that p roduced virtually identical profiles using one primer did not show increase d differentiation when using two or more primers, demonstrating that in som e cases, where strains of an organism are highly related there is limited a dvantage to using more than one primer in RAPD analysis.