TYPE-III SECRETION GENES IDENTIFY A PUTATIVE VIRULENCE LOCUS OF CHLAMYDIA

Four genes of Chlamydia psittaci strain guinea pig inclusion conjuncti vitis (GPIC), whose predicted products are highly homologous to struct ural and regulatory components of a contact-dependent or type III secr etion apparatus, were isolated. Related to genes present in several an imal and plant bacterial pathogens, these genes may represent a sectio n of a previously undetected chromosomal virulence locus analogous to several recently described virulence-associated type III secretion loc i. The existence of contact-dependent secretion in Chlamydia strongly suggests that these bacteria use pathogenic mechanisms that are simila r to those of other intracellular bacterial pathogens. Unlike other in tracellular bacteria, however, chlamydiae are metabolically inactive e xtracellularly and only become capable of global protein synthesis sev eral hours after infection. This implies that chlamydial contact-depen dent secretion is only active from within, uniquely after the bacteria have been internalized by eukaryotic cells. The possible role(s) of t his pathway in chlamydial pathogenesis are discussed.