N/A

The type strain of Listeria monocytogenes differs from wild-type L. monocytogenes strains in more characteristics than just the previously reported deficiency in hemolytic activity and virulence in the murine infection model. The type strain from the American Type Culture Collection (strain ATCC 15313) produces lecithinase, is hemolytic on rabbit (but not sheep) blood agar, lacks motility, and shows limited cytopathogenic effects on Caco-2 monolayers, whereas the type strain from the Special Listeria Culture Collection (strain SLCC 53) is unable to produce lecithinase, is nonhemolytic on rabbit or sheep blood agar, is motile, and shows no cytopathogenic effects on Caco-2 monolayers.

The discrepancies between the current description of the CAMP test between Listeria monocytogenes and Rhodococcus equi in the latest edition of Bergey's Manual of Determinative Bacteriology (L. monocytogenes is described as CAMP test negative with R. equi) and routine findings (positive reactions are usually described in many laboratories) make it advisable to review the current interpretation of the CAMP test to avoid confusion among people working in microbiological laboratories. Overall, 98.4% of the L. monocytogenes strains examined in this study, regardless of their source or the intensity of their hemolytic activity, displayed a synergic hemolytic reaction (CAMP phenomenon) with R. equi, indicating that L. monocytogenes can generally be considered CAMP positive with R. equi. We propose that L. monocytogenes, together with Listeria ivanovii, should be considered CAMP test positive with R. equi (circular or racket and semicircular or shovel shapes, respectively).