Incidence and principal sources of Listeria spp. and Listeria monocytogenes contamination in processed meats and a meat processing plant

The occurrence and distribution of listeriae in a meat processing plant was studied to determine the major sources and recites of contamination. Listeria monocytogenes and other Listeria spp. were isolated from 51% and 49% of samples of frozen raw meat taken from several incoming lots. Turkey necks and breasts, pork trimmings and lard were the principal sources of initial contamination. As a consequence, listeriae colonized certain processing sites where raw materials were handled and hygienic conditions were not strict Mainly tumbled meats were contaminated heavily during fumbling as the need to operate tumblers continuously did nor enable their proper cleaning and disinfection on a daily basis. Also the use of mechanically deboned turkey-neck meat in cooked sausages raised contamination at a pre-cooking stage. Listeriae survived in tumbled meats cooked in boilers at core temperatures below 70 degrees C, and in country-style sausages heated to 65-68 degrees C, in contrast listeriae were killed in oven-cooked fumbled meats and emulsion-type sausages heated to 72-75 degrees C, and in fully ripened salamis. Heat survivors appeared to be the main cause of post-process contamination as spreading of listeriae in the cutting room was restricted to processing lines where precontaminated meat products were handled. The possible reasons leading to heat survival of listeriae and the measures taken to control the problem were discussed. (C) 1999 Academic Press.