Early trafficking events of Mycobacterium ulcerans within Naucoris cimicoides

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Abstract
The severe skin-destructive disease caused by Mycobacterium ulcerans, named Buruli ulcer, is the third most important mycobacterial disease in humans after tuberculosis and leprosy. Recently we demonstrated that M. ulcerans could colonize the salivary glands of the water bug, Naucoris cimicoides. In this study, we report that M. ulcerans may be delivered from the digested prey aspirate to the coelomic cavity via a unique headspace, the head capsule (HC). During the infected meal, we observed that M. ulcerans clusters adhered to the stylets that were retracted in the HC at the end of the meal. M. ulcerans was able to translocate from the HC to the coelomic cavity where it is phagocytosed by the plasmatocytes. These cells are subverted as shuttle cells and deliver M. ulcerans to the salivary glands. At this early stage of its parasitic life style, two other important features of M. ulcerans can be documented: first, mycolactone is not required for translocation of M. ulcerans into the HC, in contrast to the next step, colonization of the salivary glands; second, M. ulcerans clusters bind a member of the serpin protein family present in the salivary gland homogenate.