Occurrence of Listeria monocytogenes in a meat-processing plant

The aim of the study was to evaluate the occurrence of Listeria monocytogenes in a selected meat-processing plant during processing. A total amount of 393 swab samples Were collected, including 240 from pork and beef carcass halves/quarters, 36 from meat pieces, 4 from pork tongues, 9 from saline and 104 from the environment and equipment of two production areas. The samples were swabbed and processed according to the PN EN ISO 11290-1 standard and this method enabled 207 strains of L. monocytogenes to be isolated. The environment and equipment of both beef and pork processing areas were shown to be contaminated to similar degrees (about 26%) and this contamination was higher than was observed in carcass halves and meat (about 15%). L. monocytogenes were detected on the surface of 75% of beef carcass quarters-almost three times more often than in the beef processing area (26%) and the haunch parts indicted the highest contamination (50%). Pork carcass halves were half as contaminated as beef carcass quarters and ham and neck parts showed the highest degree of contamination (22.1% and 16.2%, respectively). L. monocytogenes were isolated most frequently from the floors of both processing areas (62.5%) and cold room door handles and were noted twice as often in the beef-processing (57.1%) as in the pork processing area (25%). One positive sample was reported in the case of a table and a knife (pork area) and a saw and a hook (beef area). Hooks and a skinning machine in the pork area were contaminated more often (25% and 38%, respectively). The highest level of contamination was observed in saline and pork tongues and affected 100% of samples. The method of sample collection from the surfaces which was applied in the study turned out to be a very promising tool for gathering data on L. monocytogenes contamination, and one which could be used while introducing HACCP systems and designing 'in-plant' schemes for cleaning and disinfecting processing environments.