Vibrio parahaemolyticus effector proteins suppress inflammasome activation by interfering with host autophagy signaling.

Bacterial pathogens utilize pore-forming toxins or sophisticated secretion systems to establish infection in hosts. Recognition of these toxins or secretion system by nucleotide-binding oligomerization domain leucine-rich repeat proteins (NLRs) triggers the assembly of inflammasomes, the multiprotein complexes necessary for caspase-1 activation and the maturation of inflammatory cytokines such as IL-1ß or IL-18. Here we demonstrate that both the NLRP3 and NLRC4 inflammasomes are activated by thermostable direct hemolysins (TDHs) and type III secretion system 1 (T3SS1) in response to V. parahaemolyticus infection. Furthermore, we identify T3SS1 secreted effector proteins, VopQ and VopS, which induce autophagy and the inactivation of Cdc42, respectively, to prevent mainly NLRC4 inflammasome activation. VopQ and VopS interfere with the assembly of specks in infected macrophages. These data suggest that bacterial effectors interfere with inflammasome activation and contribute to bacterial evasion from the host inflammatory responses.

Leptospiral outer membrane protein LMB216 is involved in enhancement of phagocytic uptake by macrophages.

Leptospira interrogans is responsible for the zoonotic disease leptospirosis. The pathogenic mechanisms of this spirochaete remain poorly understood; however, virulence has been correlated with increased phagocytic uptake and survival within macrophages. Leptospiral outer membrane proteins are thought to be responsible for persistence in vivo via interaction with specific host components. In this study, we analysed the transcriptional profile of a virulent strain and its culture-attenuated derivative strain to identify bacterial factors that may be involved in pathogenesis. Two outer membrane proteins, LMB216 and LigB (leptospiral immunoglobulin-like protein B) were downregulated more than 10-fold in the culture-attenuated strain. We show that both proteins play a role in leptospiral uptake by macrophages and that LMB216, as well as LigB, enhances the binding of leptospires to fibronectin. Taken together, our results indicate that LMB216 plays a role in pathogen interaction with host molecule/s, which may contribute to pathogenesis of leptospirosis.

Inflammasome activation via intracellular NLRs triggered by bacterial infection.

Members of the nucleotide-binding, oligomerization domain (NOD)-like receptor (NLR) proteins assemble into a multiprotein platform, known as the inflammasome, to induce caspase-1 activation followed by the subsequent secretion of IL-1ß and IL-18. In this review, we focus on the role of NLRs in inflammasome activation as part of the host defence against bacterial pathogens. One of activators of the NLRC4 inflammasome is bacterial flagellin secreted through type III or IV secretion systems, which are important for the pathogenicity of many Gram-negative bacteria. The NLRP3 inflammasome is mainly activated by a large number of bacterial pore-forming toxins. Despite our knowledge of inflammasome activation upon bacterial infection, the function of antibacterial defence under in vivo conditions remains to be elucidated. Further understanding of NLR function should provide new insights into the mechanisms of host pro-inflammatory responses and the pathogenesis of bacterial infections.

Complete Genome Sequences of Low-Passage Virulent and High-Passage Avirulent Variants of Pathogenic Leptospira interrogans Serovar Manilae Strain UP-MMC-NIID, Originally Isolated from a Patient with Severe Leptospirosis, Determined Using PacBio Single-Molecule Real-Time Technology.

Here, we report the complete genome sequences of low-passage virulent and high-passage avirulent variants of pathogenic Leptospira interrogans serovar Manilae strain UP-MMC-NIID, a major causative agent of leptospirosis. While there were no major differences between the genome sequences, the levels of base modifications were higher in the avirulent variant.

Lose the battle to win the war: bacterial strategies for evading host inflammasome activation.

The inflammasome is composed of nucleotide-binding, oligomerization domain (NOD)-like receptor (NLR) proteins, and leads to caspase-1 activation and subsequent secretion of the proinflammatory cytokines interleukin 1ß (IL-1ß) and interleukin-18 (IL-18). After certain pathogenic bacteria infect host cells, such as macrophages, NLR-mediated inflammasome activation is triggered to form part of the host defenses against the invading pathogens. However, recent evidence has shown that bacteria have strategies for evading inflammasome activation in host cells. In this review, we focus on NLR-mediated inflammasome activation and bacterial evasion of the inflammasome as part of the battle between the host defenses and pathogens.