Quantitative Detection of Escherichia coli O157:H7 in ground beef by the polymerase chain reaction

A method for quantitative detection of Escherichia coli O157:H7 based on the polymerase chain reaction (PCR) was developed. The method used the NIH Image 1·61 software program to quantitatively analyse the intensity of the fluorescent image of the amplified PCR product. Based on the PCR with SLT1 and SLT2 primers used separately, a log-linear relationship between the numbers of cfu of E. coli O157:H7 inoculated into ground beef and the intensity of the PCR products was achieved with and without enrichment. Without enrichment, 150 cfu of E. coli O157:H7 per gram of ground beef were detected. In contrast, the detection limit decreased to 1·2 cfu g−1 of ground beef using SLT1 and SLT2 primers after 4·5 h of enrichment using modified EC broth with 20 μg ml−1 of novobiocin