Theoretical fragment length (bp) Actual fragment length (bp) of O157:H7 Actual fragment length (bp) of K-12 Restriction enzyme Hha I Hae III Hha I Hae III Hha I Hae III E.coli with 41 F – Eco R primer set 359 204 372 216 361 198 112 167 118 169 118 167   75   85   89   25   nd*   nd *because they were smaller than the lower limit of detection

Table 4: Theoretical and actual fragment length of PCR products amplified with the 41F-Eco-R primer set and digested with HhaI and HaeIII in E. coli.