Use of PFGE to characterize clonal relationships among Belgian clinical isolates of Listeria monocytogenes.

The Belgian Listeria Reference Centre receives between 30 and 50 human clinical strains of Listeria monocytogenes per year. In general, epidemiological data are absent or incomplete, preventing recognition of episodes of listeriosis. However, data on a clonal relationship between strains can indirectly give an idea of the occurrence of episodes. Human isolates of L. monocytogenes from 2001 were serotyped, their arsenic-cadmium resistance profiles were determined, and they were pulsotyped with the application of pulsed-field gel electrophoresis using AscI and ApaI restriction endonucleases. On five occasions, two or more strains presented the same serovar, metal-resistance profile and pulsovar, suggesting a clonal relationship. This is the first report to identify accurately potential listeriosis episodes occurring in Belgium.