[Hemolysins of Listeria monocytogenes demonstrable by activation with 2-mercaptoethanol]

Jones and Seeliger with the endorsement of the International Committee on Systematic Bacteriology, Subcommittee on the Taxonomy of Listeria, are considering to replace L. monocytogenes ATCC 15313 as prototype strain of species because of the lack of hemolytic activity in conventional agar blood media. We demonstrate in this work that ATCC 15313 strain is able to induce hemolysis in conventional media under microaerophilic conditions and also has a definite hemolytic activity when supernatants of a 24 hs growth in brain heart infusion plus 0.5% dextrose were activated with 2-mercaptoethanol (Table 3). Thirteen strains previously identified as L. monocytogenes were studied. Nine of them are compatible with the identification of L. monocytogenes, all show hemolytic activity under microaerophilic conditions, ATCC 15313 does nos show hemolysis on surface test but induces hemolysis, as other nine strains do, when activated by 2-mercaptoethanol. It is interesting to reinforce the need to perform all the different test to analyze hemolytic activity as a basis for presumptive L. monocytogenes identification. The absence of demonstrable hemolysis using all proposed test is an important factor to be taken into account for Listeria identification.