Listeria ivanovii is a species of bacteria in the genus Listeria. The listeria are rod-shaped bacteria and become positively stained when subjected to Gram staining. Of the six bacteria species within the genus, L. ivanovii is one of the two pathogenic species (the other being L. monocytogenes). It behaves like Listeria monocytogenes, but is found almost exclusively in ruminants (mainly sheep). The species is named in honor of Bulgarian microbiologist Ivan Ivanov.