Combined PCR and slot blot assay for detection of Salmonella and Listeria monocytogenes

Detection of Salmonella typhimurium and Listeria monocytogenes by the polymerase chain reaction (PCR) assay coupled with slot blot detection was investigated in this study. After being extracted from diluted bacterial culture with the extraction buffer, bacterial DNA was subjected to PCR. The slot blot assay was optimized and used to detect PCR products. The lowest detection level of this method was 103 cfu/ml in the original culture media for both pathogens, or 5 bacterial cells in the PCR reaction. Combined with immunomagnetic separation (IMS) to separate and concentrate bacteria from samples, the detection limit could be 40 cfu/ml of bacteria from milk samples. The whole detection procedure was completed within 7 h. After multiplex PCR (amplification of DNA from two different bacteria in the same PCR tube) and slot blot, a detection level of 103 cfu/ml was achieved in the simultaneous detection for both pathogens, which was similar to that of individual detection for each pathogen. The combination of PCR and slot-blot seems to be highly sensitive and time-efficient, and is therefore promising for routine use in the detection of Salmonella and L. monocytogenes in food samples such as milk.