The detection of viable vegetative cells of Bacillus sporothermodurans using propidium monoazide with semi-nested PCR

Bacillus sporothermodurans produces highly heat-resistant spores that can survive ultra-high temperature (UHT) treatment in milk. Therefore, we developed a rapid, specific and sensitive semi-nested touchdown PCR assay combined with propidium monoazide (PMA) treatment for the detection of viable B. sporothermodurans vegetative cells. The semi-nested touchdown PCR alone proved to be specific for B. sporothermodurans, and the achieved detection limit was 4 CFU/mL from bacterial culture and artificially contaminated UHT milk. This method combined with PMA treatment was shown to amplify DNA specifically from viable cells and presented a detection limit of 10(2) CFU/mL in UHT milk. The developed PMA-PCR assay shows applicability for the specific detection of viable cells of B. sporothermodurans from UHT milk. This method is of special significance for applications in the food industry by reducing the time required for the analysis of milk and dairy products for the presence of this microorganism.