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PubMed2003

Secretion of the toxin ExoU is a marker for highly virulent Pseudomonas aeruginosa isolates obtained from patients with hospital-acquired pneumonia.

Overall, hospital-acquired pneumonia (HAP) caused by Pseudomonas aeruginosa is associated with high attributable mortality. Although the intrinsic virulence of P. aeruginosa undoubtedly contributes to this phenomenon, it is unclear whether all strains share this property or whether only a subpopulation of strains are capable of causing such severe disease. In this study, the virulence of 35 P. aeruginosa isolates obtained from patients with HAP by use of a cytolytic cell-death assay, an apoptosis assay, and a mouse model of pneumonia. The virulence of individual isolates differed significantly from one to another in each of these assays. Increased virulence was associated with the secretion of ExoU, a toxin transported by the P. aeruginosa type III secretion system. Secretion of ExoS or ExoY, 2 other proteins transported by this system, was not consistently associated with increased virulence. Together, these findings suggest that secretion of ExoU is a marker for highly virulent strains of P. aeruginosa.

Animals↗
PubMed2001

Pathogenicity of Legionella pneumophila.

The bacterium Legionella pneumophila is the principal etiologic agent of Legionnaires' disease, a form of lobar pneumonia. Ubiquitous in aquatic environments, the gram-negative Legionella organism is a facultative, intracellular parasite of protozoa. The pathogenesis of legionellosis is largely due to the ability of L. pneumophila to invade and grow within alveolar macrophages, and it is widely believed that this ability results from a prior adaptation to intracellular niches in nature. Indeed, intracellular legionellae display a remarkable capacity to avoid endosomal and lysosomal bactericidal activities and to establish a unique replicative phagosome. In recent years, much progress has been made toward identifying the bacterial factors that promote intracellular infection and virulence. Surface structures that enhance infection include LPS, flagella, type IV pili, an outer membrane porin, and the Mip propyl-proline isomerase. Both type II and type IV protein secretion systems are critical for L. pneumophila pathogenesis. Whereas the type II (Lsp) system secretes a collection of degradative enzymes, the type IV (Dot/Icm) system likely exports effector proteins that are especially critical for trafficking of the Legionella phagosome. In addition to facilitating pilus formation and type II secretion, the inner membrane prepilin peptidase (PilD) of L. pneumophila appears to mediate a third, potentially novel pathway that is operative in the mammalian host. Periplasmic and cytosolic infectivity determinants include a catalase-peroxidase and the HtrA and Hsp60 stress-response proteins. The stationary phase response and the iron acquisition functions of L. pneumophila also play key roles in pathogenesis, as do a number of other loci, including the pts, mil and enh genes.

Animals↗
PubMed1999

Yersinia enterocolitica type III secretion-translocation system: channel formation by secreted Yops.

'Type III secretion' allows extracellular adherent bacteria to inject bacterial effector proteins into the cytosol of their animal or plant host cells. In the archetypal Yersinia system the secreted proteins are called Yops. Some of them are intracellular effectors, while YopB and YopD have been shown by genetic analyses to be dedicated to the translocation of these effectors. Here, the secretion of Yops by Y.enterocolitica was induced in the presence of liposomes, and some Yops, including YopB and YopD, were found to be inserted into liposomes. The proteoliposomes were fused to a planar lipid membrane to characterize the putative pore-forming properties of the lipid-bound Yops. Electrophysiological experiments revealed the presence of channels with a 105 pS conductance and no ionic selectivity. Channels with those properties were generated by mutants devoid of the effectors and by lcrG mutants, as well as by wild-type bacteria. In contrast, mutants devoid of YopB did not generate channels and mutants devoid of YopD led to current fluctuations that were different from those observed with wild-type bacteria. The observed channel could be responsible for the translocation of Yop effectors.

Amino Acid Sequence↗