Evaluation of the Magnetic Immuno PCR Assay for Rapid Detection of Salmonella

A new technique, the Magnetic Immuno PCR Assay (MIPA), has been developed for the detection of Salmonella. The assay utilizes magnetic particles coated with monoclonal antibodies against Salmonella to extract these bacteria from the sample. Trapped bacteria are lysed, and the supernatant, which contains bacterial DNA, is then subjected to the polymerase chain reaction (PCR) using primers from the Salmonella typhimurium origin of DNA replication to amplify a 163 bp region. The specificity of the primer set was tested in the PCR; amplification occurred with all 25 Salmonella strains tested but not with 19 other species of Enterobacteriaceae tested. A sensitivity of 100 cfu Salmonella typhimurium was achieved for the MIPA by visualization of the amplified products by ethidiumbromide stained agarose gel electrophoresis. A ten-fold higher sensitivity was obtained by Southern blotting of the amplified products. The presence of 10(7) cfu Escherichia coli did not interfere with these detection levels. The MIPA thus specifically detected 100 cfu of Salmonella within 5 h and may be potentially useful for rapid detection of Salmonella in clinical specimens and food.