Repression of motility and flagellin production at 37 degrees C is stronger in Listeria monocytogenes than in the nonpathogenic species Listeria innocua.

Listeria monocytogenes and Listeria innocua differ markedly in virulence but are indistinguishable by classical taxonomic criteria. Both species are actively motile and produce abundant flagellin at 22 degrees C. We have found, however, noticeable differences between L. monocytogenes and L. innocua in motility and flagellin production at 37 degrees C. At this temperature, L. monocytogenes strains were virtually nonmotile and produced little or no detectable flagellin, whereas strains of L. innocua were frequently motile and produced substantial amounts of flagellin. This flagellin was recognized by a Listeria genus-specific monoclonal antibody that also recognized flagellin produced at 22 degrees C. These results suggest differential regulation of flagellin production between L. monocytogenes and L. innocua at 37 degrees C.