Bacterial secreted proteins are required for the internalization of Campylobacter jejuni into cultured mammalian cells

Presented here is the first evidence that Campylobacter jejuni secrete prot eins upon co-cultivation with host cells and in INT 407 cell-conditioned me dium. A C. jejuni gene designated ciaB for Campylobacter Invasion antigen B was identified, using a differential screening technique, which is require d for this secretion process and the efficient entry of this bacterium into a host cell. The C. jejuni ciaB gene encodes a protein of 610 amino acids with a calculated molecular mass of 73 154 Da. The deduced amino acid seque nce of the CiaB protein shares similarity with type III secreted proteins a ssociated with the invasion of host cells from other more extensively chara cterized bacterial pathogens. In vitro binding and internalization assays r evealed that the binding of C. jejuni ciaB null mutants was indistinguishab le from that of the parental isolate, whereas a significant reduction was n oted in internalization. Confocal microscopic examination of C. jejuni-infe cted cells revealed that CiaB was translocated into the cytoplasm of the ho st cells. Culturing C. jejuni with INT 407 cells or in INT 407-conditioned medium resulted in the secretion of at least eight proteins, ranging in siz e from 12.8 to 108 kDa, into the culture medium. C. jejuni ciaB null mutant s were deficient in the secretion of all eight proteins, indicating that Ci aB is required for the secretion process. The identification of the C. jeju ni ciaB gene represents a significant advance in understanding the molecula r mechanism of C, jejuni internalization and the pathogenesis of C. jejuni- mediated enteritis.