Survival of Campylobacter jejuni in Acanthamoebae castellanii provides mechanistic insight into host pathogen interactions.

Campylobacter jejuni is the leading cause of bacterial foodborne gastroenteritis world-wide but is rarely transferred between human hosts. Although a recognized microaerophile, C. jejuni is incapable of growing in an aerobic environment. The persistence and transmission of this pathogen outside its warm-blooded avian and mammalian hosts is poorly understood. Acanthamoebae species, are predatory protists and form an important ecological niche with several bacterial species. Here, we investigate the interaction of C. jejuni and Acanthamoebae castellanii at the single-cell level. We observe that a subpopulation of C. jejuni cells can resist killing by A. castellanii and non-digested bacteria are released into the environment where they can persist. In addition, we observe that A. castellanii can harbor C. jejuni even upon encystment. Transcriptome analyses of C. jejuni interactions revealed similar survival mechanisms when infecting both A. castellanii and warm-blooded hosts. In particular, nitrosative stress defense mechanisms and flagellum function are important as confirmed by mutational analyses. This study describes a new host-pathogen interaction for C. jejuni and confirms that amoebae are transient hosts for the persistence, adaptability and potential transmission of C. jejuni.