Comparison of the efficacy of different techniques, culture media, and sources of blood in determining the hemolytic activity of Listeria spp.

Hemolytic activity is a fundamental criterion for the differentiation of Li steria species; therefore, a simple and inexpensive procedure to clearly di stinguish hemolytic strains from each other and from nonhemolytic strains w ould be of great aid. We compared the efficacy of several techniques, cultu re media, and types of blood in demonstrating the hemolysis of Listeria spp . The hemolytic activities of Listeria monocytogenes and Listeria seeligeri were more easily detected with a red blood cell top-layer (RBCTL) techniqu e and with a microplate technique than when the strains were streaked on bl ood agar (BA). Listeria ivanovii produced a marked hemolysis regardless of the technique employed. In general, the hemolytic activity of these three s pecies was stronger on media containing brain heart infusion (BHI) agar and (or) potassium tellurite (PT). However, Listeria innocua produced question able hemolytic reactions when nonselective culture media with BHI and PT we re utilized, limiting the advantages gained by employing the two compounds. The RBCTL and the BA techniques disclosed greater hemolytic activity for L . monocytogenes, L. seeligeri, and L. ivanovii with sheep and guinea pig bl ood than with horse and human blood. When the microplate technique was used , all four kinds of blood were equally effective.