EVALUATION OF AN ENZYMATIC METHOD FOR FAST IDENTIFICATION OF LISTERIA-SPP IN CHEESE AND MEAT-PRODUCTS

Listeria-Tek ELISA was compared with conventional cultural procedure of FIL/IDF (Federation International de Laiterie/International Dairy Federation) modified by us. The ELISA assay is able to detect Listeria innocua, Listeria monocytogenes, Listeria murrayi and Listeria welshimeri, after 48 h in artificially contaminated cheeses. No specific reactions, no false positive or negative were detected and the assay has a high correlation with the conventional method used in this research. We also analyzed meat products and cheeses and identified Listeria spp. and Listeria monocytogenes serotypes. In 313 food samples examined there were only 3 false positives. With ELISA Kit we obtained 0.9% more than with the cultural method and the percentage of false positives is 1.6%. So in commercial products the total absence of false negatives demonstrates the great sensitivity of the method in respect to investigated microorganisms. As determined by cultures 218 samples contained 47 Listeriae monocytogenes, 67 Listeriae innocua, 21 Listeriae welshimeri, 7 Listeriae ivanovii, 3 Listeriae murrayi and 3 Listeriae denitrificans. Listeria monocytogenes includes serotypes 1 (13) and serotypes 4 (14). 20 Listeriae monocytogenes were serotyped by polyantisera Difco (Detroit, Michigan).