Interactions of some common pathogenic bacteria with Acanthamoeba polyphaga

Protozoan grazing is a major trophic pathway whereby the biomass re-enters the food web. Nonetheless, not all bacteria are digested by protozoa and the number known to evade digestion, resulting in their environmental augmentation, is increasing. We investigated the interactions of Bacillus cereus, Enterococcus faecalis, Enteropathogenic Escherichia coli (EPEC), Listeria monocytogenes, Salmonella enterica serovar Typhimurium, and methicillin-sensitive Staphylococcus aureus (MSSA), with the amoeba, Acanthamoeba polyphaga. There was evidence of predation of all bacterial species except L. monocytogenes and S. aureus, where extracellular numbers were significantly higher when cultured with amoebae compared with growth in the absence of amoebae. Intracellular growth kinetic experiments and fluorescent confocal microscopy suggest that S. aureus survived and may even multiply within A. polyphaga, whereas there was no apparent intra-amoebal replication of L. monocytogenes and higher numbers were likely sustained on metabolic waste products released during coculture.