New method for the isolation of Listeria monocytogenes from contaminated samples.

A new method for the isolation of Listeria monocytogenes from samples contaminated with other bacteria is described. The method requires 10 to 11 days and is based on the motility of listeriae in semisolid selective medium. The new method was compared with isolation techniques described by Füzi and Pilis and by Ralovich et al. All 30 faecal samples containing 100 listeriae per g of faeces were shown positive by the new method. Using the method of Ralovich et al. the same positivity ratio could be obtained only with samples containing 1000 listeriae per g of faeces. At a contamination rate of 10000 listeriae per g of faeces 28 out of 30 faecal samples were positive by the method of Füzi and Pilis. The new method gave 10 to 86% positivity when 775 faecal samples from 10 animal species were tested.