An aliquot of 100 μl of each of the 10 fold dilutions was spread plated on Oxoid chromogenic Listeria agar (OCLA) (Oxoid, CM1084B Basingstoke, UK) supplemented with OCLA selective supplement (SR0226E) and Brilliance Listeria differential supplement (SR0228E) and left for incubation at 37 °C for 48 h