Novel mechanism for the CAMP reaction between Listeria monocytogenes and Corynebacterium equi

The synergistic hemolytic reaction between Listeria monocytogenes, Staphylococcus aureus and Corynebacterium equi on blood agar plates was explored using a modified test-tube assay. A synergistic lysis of sheep red blood cells was observed with L. monocytogenes and either S. aureus or C. equi, using crude extracts. Synergism was also found with L. monocytogenes and purified cholesterol oxidase from Pseudomonas fluorescens and Brevibacterium brevi. Crude extracts of S. aureus sensitized sheep red blood cells to subsequent lysis with either L. monocytogenes or C. equi. The interaction between L. monocytogenes and C. equi apparently did not involve a pre-sensitization step; simultaneous exposure of sheep red blood cells to the two extracts was required. A number of strains of L. monocytogenes gave positive synergistic reactions with cholesterol oxidase, suggesting that this reaction may be more useful than the CAMP test with C. equi for identifying L. monocytogenes. These results suggest that a novel synergistic reaction may be taking place, possibly involving the listeriolysin O, or one or both of the phospholipases from L. monocytogenes.