Abstract: A droplet digital polymerase chain reaction (ddPCR) method was developed for the rapid and quantitative detection of Escherichia coli O157:H7 in foods. A pair of primers and a probe were designed specific for the single copy gene of hlyA in E. coli O157:H7. The specificity, sensitivity and repeatability of this method were evaluated. At the same time, the plate counting method, real-time PCR and the ddPCR method were compared through the detection of artificially contaminated salmon samples using them. The results indicated that the ddPCR method had excellent specificity, sensitivity and repeatability in E. coli O157:H7 detection. The limit of detection (LOD) and limit of quantification (LOQ) for pure bacterial culture were 105 and 25 CFU/mL, respectively. The sensitivity of this developed method was 110 CFU/g in artificially contaminated salmon samples. At different levels of artificial contamination in salmon samples, there was no significant difference (P > 0.05) between the results of ddPCR and plate counting, which were more stable and accurate than the results of real-time PCR. Therefore, the established ddPCR method can detect E. coli O157:H7 in food samples more rapidly, accurately, sensitively and specifically.

Key words: Escherichia coli O157:H7; droplet digital polymerase chain reaction; real-time polymerase chain reaction; limit of quantification; limit of detection