Hindawi Publishing Corporation Journal of Biomedicine and Biotechnology Volume 2012, Article ID 954375, 9 pages doi:10.1155/2012/954375 Research Article Cytotoxicity of Bacterial Metabolic Products, including Listeriolysin O, on Leukocyte Targets R. Stachowiak, 1 M. Lyzniak, 2 B. K. Budziszewska, 3 K. Roeske, 1 J. Bielecki, 1 G. Hoser, 2 and J. Kawiak 2 1 Department of Applied Microbiology, University of Warsaw, 02-096 Warsaw, Poland 2 Department of Clinical Cytology, Medical Centre of Postgraduate Education, 01-813 Warsaw, Poland 3 Department of Haematology, Institute of Haematology and Transfusion Medicine, 02-776 Warsaw, Poland Correspondence should be addressed to J. Kawiak, jkawiak@cmkp.edu.pl Received 22 May 2012; Accepted 24 July 2012 Academic Editor: Frederick D. Quinn Copyright © 2012 R. Stachowiak et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Bacterial toxins can exhibit anticancer activities. Here we investigated the anticancer effects of the listeriolysin O toxin produced by Listeria monocytogenes. We found that supernatants of Listeria monocytogenes strains (wild type, 1189, and 1190) were cytotoxic to the Jurkat cell line and human peripheral blood mononuclear cells (PBMC) in a concentration-dependent manner. The supernatant of strain 1044, not producing listeriolysin O, was inactive. The supernatants of Listeria strains were also cytotoxic toward B cells of chronic leukemia patients, with no significant differences in activities between strains. We also tested supernatants of Bacillus subtilis strains BR1-90, BR1-S, and BR1-89 producing listeriolysin O. BR1-S and BR1-89 were cytotoxic to PBMC and to Jurkat cells, the latter being more sensitive to the supernatants. BR1-90 was not hemolytic or cytotoxic to PBMC, but was cytotoxic to Jurkat cells in the concentration range of 10–30%, suggesting that listeriolysin O is selectively effective against T cells. Overall, the response of human peripheral blood mononuclear and human leukemia cell lines to bacteria supernatants containing listeriolysin O depended on the bacteria strain, target cell type, and supernatant concentration. 1. Introduction The anticancer role of bacteria was recognized over a hun- dred years ago, when the American physician William Coley began the first well-documented use of bacteria and their toxins to treat end-stage cancers. He developed a safe vaccine composed of killed bacteria species [1], which was used to successfully treat sarcomas, carcinomas, lymphomas, and melanomas [2]. Most pathogenic bacteria produce toxins; these impor- tant pathogenic factors are generally proteins with enzymatic activity that can be classified into several groups. The first class includes hydrolytic enzymes, such as phospholipases, proteases, metalloproteases, glycosidases, deaminases, and deoxyribonucleases, which disrupt target molecules. Another class interferes with host metabolism modifies metabolic components; this group includes transferases, such as glu- cosyl transferases and ADP-ribosylating toxins, or lyases like adenylate cyclase [3]. A third group of toxins, the cytolysins, acts on the cytoplasmic membranes, without enzymatic activity or intracellular penetration; this group includes receptor-targeted toxins and membrane-damaging toxins, which are produced by numerous Gram-positive and Gram-negative bacteria. Cytolysins may combine cytolytic abilities with enzymatic activity, and some phospholipases can hydrolyze lipids in the cell membrane together with membrane-lysing activity. Pore-forming cytolysins are membrane-damaging toxins without enzymatic activity. These highly specialized proteins damage target cells by inserting hydrophobic regions into the cellular membrane phospholipid bilayer [3]. The largest and most homogenous group of pore-forming cytolysins are the cholesterol-dependent cytolysins (CDCs). The CDCs are exclusively produced by Gram-positive pathogens, and share similar amino acid sequences and biochemical properties [4]. Like other toxins, CDCs are usually secreted by a bacterial cell such that their activity can be directly exerted on eukaryotic cells. Efficient secretion machinery is typical for