Molecular Typing of Listeria monocytogenes Isolated from Different Sources by Pulsed-Field Gel Electrophoresis

A total of 30L monocytogenes strains from different sources including 13 strains isolated from the foreign imported meat were genotyped in order to establish their genetic relatedness and to compare them with the foreign isolates. PFGE analysis of genomic DNA showed the $11\~16$ fragments ranging in size from 38 to 504 kb. Eleven different PFGE types $(1\~11)$ were identified in the dendrogram at $75\%$ similarity, and the two major PFGE types, type 1 and 2, contained $94\%$ of domestic isolates (16/17). All isolates from domestic beef and pork carcass were grouped in each different type, however, isolates from chicken were clustered together with those from pork and beef. We also found all foreign strains were unrelated with each other, regardless of geographic criteria and that they could be differentiated from those from the domestic isolates by PFGE pattern. The PFGE pattern of one isolate from chicken wing, which the chicken meat was found to be imported from foreign country, was closely related to that of isolate from the Thailand.