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Aims:  A rapid and sensitive method for Listeria monocytogenes direct detection from milk was developed. It is based on a magnetic capture hybridization procedure for selective DNA purification, followed by PCR identification. A comparison with two similar commercial systems from Dynal (Dynabeads) was carried out. Methods and Results:  The technique used previously developed nanoparticles modified with a 21‐mer oligonucleotide. This sequence, sharing homology with all the L. monocytogenes strains, was selected on hlyA gene and located outside the desired specific PCR site to avoid cross‐contaminations. Capture probe properties, in term of spacer length and purification, were determined to obtain the highest hybridization efficiency. Its specificity was tested in hybridization experiments with nontarget bacterial species. Any inhibitory effect of the nanoparticles on PCR was also examined. The amplification performed with the purified DNA could reliably identify a 10 CFU ml−1 contamination rate. Conclusions:  The optimized purification method showed a high specificity and sensitivity, with a detection level one log more sensitive than PCR carried out with nucleic acids obtained using commercial nanoparticles. Significance and Impact of the Study:  The method, avoiding pre‐enrichment, provides a rapid alternative to conventional microbiological detection methods. Furthermore, it is suitable for automation and can be proposed for the screening of a large number of samples.

Plasmids are the main vectors of resistance and virulence genes in Enterobacteriaceae and plasmid typing is essential for the analysis of evolution, epidemiology and spread of antibacterial resistance. The PCR-Based Replicon Typing (PBRT), developed by Carattoli et al. in 2005, was an efficient method for plasmid identification and typing in Enterobacteriaceae. The 2005 PBRT scheme detected 18 replicons in 8 PCR reactions. Recently, the identification of novel replicons and plasmid types requested an update of the PBRT scheme. A commercial PBRT-KIT was devised for the identification of 28 different replicons in 8 multiplex PCRs. Here we report sensitivity and specificity of the PBRT-KIT carried out in comparison with the 2005 PBRT. The analysis of plasmid content was performed on forty-two enterobacterial strains from different sources, containing different replicon content. The 2005 PBRT identified replicons in 76.2% of the strains. The PBRT-KIT detected replicons in 100% of the analyzed strains, demonstrating increasing sensitivity and specificity of the commercial test with respect to the former 2005 PBRT scheme.

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