Purpose: The objective of present study was to investigate the prevalence and genetic correlations of L. monocytogenes in cattle and pig farms in S. Korea.
Methods: Feces, soil, silage (cattle farm), and sludge (pig farm) samples (n=2,018) were collected from 25 cattle and pig farms, which were visited 2-3 times. L. monocytogenes were isolated by plating the samples on PALCAM agar, and presumptive colonies were identified by amplifying Listeria-specific genes (hly and prs) by PCR and by 16s rRNA analysis. All L. monocytogenes isolates were then serotyped by multiplex PCR and agglutination assay. Virulence genes (inlA, inlB, actA, plcB, and hlyA) were identified by PCR, and genetic correlations were also evaluated by pulsed-field gel electrophoresis (PFGE) patterns digested with AscI restriction enzymes.
Results: Of 2,018 farm samples, just three samples (0.15%) were L. monocytogenes positive and isolated from soil samples in same farm. Even though the samples were from same farm, serotypes of the isolates from farms were 3a (one isolate) and 4ab (two isolates), which are low pathogenic. In PFGE patterns of L. monocytogenes, genetic correlations between same isolates (4ab) 100%, but the genetic correlation between different serotypes was only 26.3%.
Significance: These results indicate that there is very low prevalence of L. monocytogenes in cattle and pig farms. Thus, the possibility of transmission of the pathogen from farm to people is very low.