Journal of Basic Microbiology 2011, 51, 1 – 8 1 © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.jbm-journal.com Research Paper Acanthamoeba polyphaga, a potential environmental vector for the transmission of food-borne and opportunistic pathogens Immacolata Anacarso, Simona de Niederhäusern, Patrizia Messi, Elisa Guerrieri, Ramona Iseppi, Carla Sabia and Moreno Bondi Department of Biomedical Sciences, University of Modena and Reggio Emilia, Modena, Italy The endosymbiotic relationship could represent for many bacteria an important condition favouring their spread in the environment and in foods. For this purpose we studied the behaviour of some food-borne and opportunistic pathogens (Listeria monocytogenes, Staphylococcus aureus, Enterococcus faecalis, Salmonella enterica serovar Enteritidis, Aeromonas hydrophila, Yersinia enterocolitica) when internalized in Acanthamoeba polyphaga. Our results confirm the capability of the bacteria tested to grow within amoebal hosts. We can observe two types of interactions of the bacteria internalized in A. polyphaga. The first type, showed by Y. enterocolitica and A. hydro- phila, was characterized by an early replication, probably followed by the killing and digestion of the bacteria. The second type, showed by E. faecalis and S. aureus was characterized by the persistence and grow inside the host without lysis. Lastly, when amoebae were co-cultured with L. monocytogenes and S. Enteritidis, an eclipse phase followed by an active intracellular growth was observed, suggesting a third type of predator-prey trend. The extracellular count in presence of A. polyphaga, as a result of an intracellular multiplication and subsequent release, was characterized by an increase of E. faecalis, S. aureus, L. monocytogenes and S. Enteritidis, and by a low or absent cell count for Y. enterocolitica and A. hydrophila. Our study suggests that the investigated food-borne and opportunistic pathogens are, in most cases, able to interact with A. polyphaga, to intracellularly replicate and, lastly, to be potentially spread in the environment, underlining the possible role of this protozoan in food contamination. Keywords: Acanthamoeba polyphaga / Co-culture / Food-borne pathogens / Environmental reservoir Received: March 01, 2011; accepted: July 15, 2011 DOI 10.1002/jobm.201100097 Introduction * The diffusion of bacterial pathogens and their trans- mission to humans are biological processes influenced by many factors, including the physiology of the mi- croorganism and the mechanisms used for surviving in an often extra-cellular hostile environment. The re- search interest is focused on the importance of micro- bial community in the persistence of pathogens in food, since within structures like biofilm or within protozoan Correspondence: Patrizia Messi, University of Modena and Reggio Emilia, Department of Biomedical Sciences, Via Campi 287, 41125 Modena, Italy E-mail: patrizia.messi@unimore.it Phone: +39-59-2055615 Fax: +39-59-2055483 hosts can take place a series of biological interactions which may have significant implications for human health. The role of free-living protozoa as predators of bacteria is widely acknowledged, and predation by pro- tozoa has a significant effect in controlling bacterial populations in terrestrial and aquatic environments [1]. Previous authors have highlighted the key role of the intracellular life in free-living amoebae (FLA), common worldwide members of the natural microflora of plants, isolated from soil, water, air, and food [2, 3]. FLA normally phagocytise entire bacterial cells as sources of nutrition and some of the internalized bacteria may avoid phagosomal lysis and persist intracellularly [4, 5]. The resistance to digestion is a further mechanism of bacterial pathogenicity and from an evolutionary point