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The occurrence of L. monocytogenes was investigated in a factory for slaughtering, carving and meat processing - based on the humanpathogene significance of these bacteria and because Listeriosis were noticed more often within the last years. Ways of transmission and most important possibilities of contamination in the meat factory were to be described at the same time. The most important esults are summarized in the following: 1. L. monocytogenes was isolated by 237 of 1197 samples (19,8 per cent). Two strains of different serovars were found in each of two samples, so 239 L. monocytogenes strains (20,0 per cent) were proved. These results confirm the suitability of acriflavin-nalidixic-acid-agar as solid media of selection in connection with potassiumrhodanidbouillon as media of enrichment for the isolation of L. monocytogenes out of material with a high level of bacterial contamination. 2. The isolation rates of L. monocytogenes in the three parts of the factory were different. L. monocytogenes was most often proved in the part of carving with 67,1 per cent positive samples. The fewest isolation rate with 14,6 per cent positive samples was established in the part of slaughtering. There were 26,3 per cent positive samples in the part of meat processing and 23,4 per cent in the cold storage depot. . L. monocytogenes was isolated in 18,9 per cent of the investigated final products. Frosted minced meat was that final product with the highest isolation rate 80,0 per cent L. monocytogenes positive samples. 4. The distribution of serovars of 239 isolated L. monocytogenes strains shows the following: 135 strains were identified as serovar 4b (56,5 per cent) and 98 as serovar l/2a (41,0 per cent). The serovars of 6 strains (2,5 per cent) could not have been determined because of spontaneous agglutination and are classified as R-forms. So the serovar 4b was more often proved than the serovar l/2a. 5. The serotyping of the isolated L. monocytogenes strains showed that the strains of bovine (organs, meat of muscles, final products, swab of environmental area) had more often been assigned to the serovar 4b (75,9 per cent), he strains of swine (organs, meat of muscles, final products, swab of environmental area) to the serovar l/2a (60,2 per cent). 6. Nearly all isolated strains of L. monocytogenes were classified as pathogenic . Strains of the serovar 4b are considered to be virulent in particular, because approximately 75 per cent of all human Listeriosis was caused by this serovar. Hemolysin is passed as the most important factor of virulency. A hemolysis (with different intensity) was proved at all strains when examining L. monocytogenes isolates on nutrient medium of blood. An alpha hemolysis was noticed in 54,1 per cent of the serovar 4b and a beta hemolysis in 45,9 per cent. Nearly all strains of the serovar l/2a (95,9 per cent) showed an obvious beta hemolysis and sa these are also classified as potentially virulent. The serovars 1/2a and 4b could be considered as "local germs" because solely these serovars were proved in this factorv 8. L. monocytogenes is brought into the factory mainly by the slaughter cattle. L. monocytogenes get into the slaughterhouse within organs with direct contact with the outer world and contaminate the meat and production area. The germs can so be transmitted to all other parts of the factory by the L. monocytogenes contaminated meat. Under favourable circumstances L. monocytogenes can fix itself and multiply in ecological recesses. These germs contaminate meat products, sausages and similar products. 9. As long as slaughter cattle contains L. monocytogenes a meat factory is impossible to be free from Listeria, but the "fixed" L. monocytogenes germs can be eliminated. Products with very few listeriae must be aimed.