Role of acanthamoeba spp. in the environmental survival of listeria monocytogenes

Listeria monocytogenes causes a potentially deadly disease of man and is a major source of contamination in food industry. The mechanism of survival and persistence of L. monocytogenes in the environment is not fully known. The present study investigates the possible role of Acanthamoebae in the survival and persistence of L. monocytogenes in the environment. This was achieved through experiments that brings together the two organisms in a co-culture and then examined ability of bacteria to survive in the presence of amoeba, inside amoeba trophozoites and in their cysts. The effects of intracellular survival on L. monocytogenes’ morphology, ability to form biofilms and respond to biocides inside and outside the cysts were also examined. In summary, L. monocytogenes Scott A was found to survive and grow in Acanthamoeba over 72 h. In addition, exposure of bacteria to manganese enhanced intracellular growth and survival of L. monocytogenes within Acanthamoeba. While L. monocytogenes Scott A survived and replicated in A. castellanii, it barely survived in A. polyphaga and never survived in A. culbertsoni. None of the other strains of L. monocytogenes tested were able to survive in Acanthamoeba. Autophagy, which was previously shown to aid survival of L. monocytogenes in macrophages, was also found contribute to survival within Acanthamoeba. In addition to surviving within A. castellanii trophozoites, L. monocytogenes Scott A also survived encystment of the host amoeba. L. monocytogenes sequestered in cysts were protected from high level of chlorine that is lethal to free bacteria. In addition, L. monocytogenes recovered from cysts were predominantly filamentous and demonstrated enhanced ability to form biofilm and also exhibited increased resistance to a disinfectant and some antibiotics that are normally used in treatment of listerial infections. The observations suggest that A.castellanii could potentially contribute to the survival, dissemination, and persistence of bacteria in the environment.