Molecular typing by pulsed-field gel electrophoresis of Spanish animal andhuman Listeria monocytogenes isolates

A total of 153 strains of Listeria monocytogenes isolated from different so urces (72 from sheep, 12 from cattle, 18 from feedstuffs, and 51 from human s) in Spain from 1989 to 2000 were characterized by pulsed-field gel electr ophoresis. The strains of L. monocytogenes displayed 55 pulsotypes. The 84 animal, 51 human, and 18 feedstuff strains displayed 31, 29, and 7 differen t pulsotypes, respectively, indicating a great genetic diversity among the Spanish L. monocytogenes isolates studied. L. monocytogenes isolates from c linical samples and feedstuffs consumed by the diseased animals were analyz ed in 21 flocks. In most cases, clinical strains from different animals of the same flock had identical pulsotypes, confirming the existence of a list eriosis outbreak. L. monocytogenes strains with pulsotypes identical to tho se of clinical strains were isolated from silage, potatoes, and maize stalk s. This is the first study wherein potatoes and maize stalks are epidemiolo gically linked with clinical listeriosis.