Isolation and characterization of Listeria monocytogenes from the environment of three ewes' milk processing factories in Slovakia

The aim of the study was to investigate the occurence and diversity of Listeria monocytogenes in three ewes' milk processing factories in Slovakia, and to reveal its sources. A total of 639 samples from the cheese production chain were collected during the years 2011-2014, out of which 20 (3.1%) were found to be positive for L. monocytogenes. L. ivanovii. was detected in two samples and other Listeria species in 309 (48.4%) samples. Sporadic L. monocytogenes contamination was observed in all three factories with 10% positive samples being the products, while 90% of positive samples were associated with the production environment. By molecular serotyping using multiplex polymerase chain reaction, the L. monocytogenes isolates were classified in three serogroups - 80% in serogroup Ha, 10% in serogroup IIc and 10% in serogroup IVb. Testing for markers specific for three epidemic clones (ECI-ECIII) produced negative results. Molecular diversity evaluation of isolated strains by AscI-restriction and pulsed-field gel electrophoresis (PFGE) resulted in strain discrimination into 14 clusters at 100% similarity. The observed occasional incidence of L. monocytogenes and high strain diversity indicated the origin of contamination from external sources.