Rapid genotyping ofEscherichia coli O157 isolates by random amplification of polymorphic DNA

Although several typing methods have been described for Shiga-like toxin-producingEscherichia coli O157, the methods are somewhat cumbersome. Using 22 isolates ofEscherichia coli O157 and five otherEscherichia coli isolates, two primers (M13 core sequence and 970-11) were found to give excellent differentiation between isolates using random amplified polymorphic DNA (RAPD). Using only the presence or absence of variable bands, a matrix of 20 variable characters was identified. From these characters, similarity coefficients were calculated and a phenogram constructed. All of theEscherichia coli O157 isolates were easily distinguished from the non-O157Escherichia coli isolates. Using a 95% similarity cutoff, we found 13 RAPD types among the 22Escherichia coli O157 isolates. Isolates thought to be identical by toxin and phage typing as well as by epidemiological association were distinguished, and others thought to be distinct by lack of epidemiological association were identical. RAPD using M13 and 970-11 primers is a potentially useful typing tool forEscherichia coli isolates of serotype O157 and possibly otherEscherichia coli isolates.