RAPD analysis, serotyping, and esterase typing indicate that the population of Listeria monocytogenes strains recovered from cheese and from patients with listeriosis in Belgium are different.

Populations of Listeria monocytogenes strains isolated in Belgium from cheese and from patients with listeriosis were characterised by randomly amplified polymorphic DNA (RAPD) analysis using two 10-mers primers (OPA-04 and OPA-13). High discrimination levels were obtained with each of these primers alone (discrimination indices (DI) of 0.899 and 0.935 for OPA13 and OPA04, respectively) or in combination (DI of 0.960). The clustering of strains obtained by RAPD was compared with a clustering previously made using serotyping and esterase typing. RAPD allowed the subdivision of each serovar cluster and of most of the clusters determined by the polymorphism of the bacterial esterases. Our analysis indicates that the population of strains of L. monocytogenes found in cheese differs from the one isolated from patients with listeriosis during the same period.