A new capacitance medium for presumptive detection of Listeria spp. from cheese samples

The paper presents a new medium and a method for the rapid presumptive detection of Listeria spp. in cheese samples by electrical capacitance changes. The Bactometer based capacitance broth (LED medium) required a 30% change in signal within 30 h to identify presumptive positive results. Of 32 cheese samples tested, 10 were found to contain Listeria spp. using a Fraser broth screening method and 12 using the LED medium and method. The LED method also gave 16 fewer (total = 1) false presumptive positive results. Results show the LED method to be superior to Fraser broth in regard to both the number of false presumptive positive and confirmed false negative results detected. The method appears to be suitable as a reliable rapid screen for the presence of Listeria spp. in cheese.