Genetic Factors of Campylobacter jejuni Required for Its Interactions with Free-Living Amoeba

<i>Acanthamoeba</i>, a free-living amoeba ubiquitous in environmental water, has been considered as the environmental reservoir of certain bacterial pathogens, including <i>Campylobacter jejuni</i>, an intracellular human pathogen causing self-limiting gastroenteritis. <i>Acanthamoeba</i>-<i>C. jejuni</i> interaction mechanisms may help clarify how the otherwise fastidious bacterium <i>C. jejuni</i> survives in environmental waters. In this study, we constructed single deletion mutants of <i>C. jejuni</i> strain 81-176 for the 10 selected genes (<i>motAB</i>, <i>ciaB</i>, <i>kpsE</i>, <i>virB11</i>, <i>cheY</i>, <i>flaAB</i>, <i>cstII</i>, <i>docB</i>, <i>sodB</i>, and <i>cadF</i>) previously shown to be important for the interaction (invasion and intracellular survival) of <i>C. jejuni</i> with mammalian hosts. We used a modified gentamicin protection assay to quantify the internalization and intracellular survival of these mutants and the wild type with the two species of <i>Acanthamoeba</i> (<i>A. castellanii</i> and <i>A. polyphaga</i>). Both internalization and intracellular survival were significantly lower for all mutants compared to the wild type with both amoeba strains, except for <i>ΔcstII</i> in the internalization assay with <i>A. castellanii</i> (<i>p</i> < 0.05). The results of this study highlight that the mechanisms used by <i>C. jejuni</i> to interact with mammalian hosts are conserved in its interactions with amoeba hosts. This understanding may be useful in developing effective strategies to reduce the transmission of <i>C. jejuni</i> to chickens through drinking water.