EntE, EntS and TolC synergistically contributed to the pathogenesis of APEC strain E058.

Extraintestinal pathogenic Escherichia coli (ExPEC) shows an enhanced ability to cause infection outside the intestinal tract. Avian pathogenic E. coli (APEC), one type of ExPEC, causes avian colibacillosis, a disease of significant economic importance to poultry producers worldwide that is characterized by systemic infection. Some ExPEC strains as well as other pathogenic enterobacteria produce enterobactin, a catecholate siderophore used to sequester iron during infection. Here, we showed that disruption of enterobactin efflux via outer membrane protein TolC significantly decreased the pathogenicity of APEC strain E058. Furthermore, colonization and persistence assays performed using a chicken infection model showed that the ΔtolC mutant was obviously attenuated (p˂0.001). In contrast, disruption of enterobactin synthesis gene entE and/or the inner membrane transporter gene entS had little effect on pathogenicity. Analysis of growth kinetics revealed a significant reduction in the growth of triple mutant strain E058ΔentEΔentSΔtolC in iron-deficient medium compared with the wild-type strain (p˂0.001), while no growth impairment was noted for the E058ΔtolC mutant in either Luria-Bertani broth or iron-deficient medium. The E058ΔentEΔentSΔtolC mutant also showed significantly decreased virulence compared with single mutant strain E058ΔtolC. Low-copy complementation of strains E058ΔtolC and E058ΔentEΔentSΔtolC with plasmid-borne tolC restored virulence to wild-type levels in the chicken infection model. Macrophage infection assays showed that ingestion of E058ΔtolC by macrophage cell line HD11 cells was reduced compared with ingestion of the E058ΔentEΔentSΔtolC mutant. However, no significant differences were observed between the mutants and the wild-type in a chicken serum resistance assay. Together, these results suggest that EntE, EntS and TolC synergistically contributed to the pathogenesis of APEC strain E058 in an iron-deficient environment.

Lon Protease Is Involved in RhpRS-Mediated Regulation of Type III Secretion in Pseudomonas syringae.

Pseudomonas syringae depends on the type III secretion system (T3SS) to directly translocate effectors into host cells. Previously, we reported a nonpathogenic rhpS mutant, suggesting that the two-component transduction system rhpRS is an important regulator of T3SS in P. syringae. rhpRS regulates itself and a variety of downstream genes under an inverted repeat element promoter in a phosphorylation-dependent manner. Here, we identify lon as a suppressor of the rhpS mutant through transposon screening. A lon/rhpS double mutant restored the phenotypes of the rhpS mutant. The expression level of lon was higher in rhpS and other T3SS-deficient mutants than the wild-type strain, suggesting a negative feedback mechanism between lon and T3SS genes. lon was also induced by a novel T3SS inhibitor, acetate, which substantially compromises the activation of T3SS genes in minimal medium and bacterial growth in host plants.

Comparative efficacy of experimental inactivated and live-attenuated chimeric porcine circovirus (PCV) 1-2b vaccines derived from PCV1 and PCV2b isolates originated in China.

BACKGROUND: Porcine circovirus type-2b (PCV2b) is recognized as the etiological agent of the various clinical manifestations of porcine circovirus-associated disease (PCVAD). Previous studies have demonstrated effectiveness of chimeric PCV1-2 vaccines against PCV2b challenge. In this study, the efficacy of inactivated and live-attenuated (2 × 10(3.5) or 2 × 10(4.0) 50% tissue culture infective dose [TCID50] dose) chimeric PCV1-2b vaccines was compared side-by-side in conventional pigs. METHODS: Twenty-seven non-PCV2 viremic pigs without PCV2-specific antibody were randomly divided into six groups, including four vaccinated and challenged groups, a nonvaccinated challenged group, and a mock group. All pigs except those in the mock group were challenged at 28 days post vaccination (DPV) using PCV2b. RESULTS: Both inactivated and live-attenuated chimeric PCV1-2b vaccines induced a robust antibody responses, and significantly decreased microscopic lesion and lower viral loads in serum or superficial inguinal lymph nodes (SILN) compared with that in the nonvaccinated challenged group. PCV2 antibody titers decreased after 7 days post challenge (DPC) in pigs administered the inactivated PCV1-2b vaccine and they were lower than those in pigs inoculated with live-attenuated PCV1-2b on the day of necropsy. Moreover, no viremia was present in pigs inoculated with live-attenuated PCV1-2b vaccine at 21 DPC regardless of the dose difference. CONCLUSIONS: The results demonstrated that both inactivated and live-attenuated chimeric PCV1-2b vaccines were effective to induce protective immunity against PCV2b infection.

The transfer-messenger RNA-small protein B system plays a role in avian pathogenic Escherichia coli pathogenicity.

Extraintestinal pathogenic Escherichia coli (ExPEC) is capable of colonizing outside of the intestinal tract and evolving into a systemic infection. Avian pathogenic E. coli (APEC) is a member of the ExPEC group and causes avian colibacillosis. Transfer-mRNA-small protein B (tmRNA-SmpB)-mediated trans-translation is a bacterial translational control system that directs the modification and degradation of proteins, the biosynthesis of which has stalled or has been interrupted, facilitating the rescue of ribosomes stalled at the 3' ends of defective mRNAs that lack a stop codon. We found that disruption of one, or both, of the smpB or ssrA genes significantly decreased the virulence of the APEC strain E058, as assessed by chicken infection assays. Furthermore, the mutants were obviously attenuated in colonization and persistence assays. The results of quantitative real-time reverse transcription-PCR analysis indicated that the transcription levels of the transcriptional regulation gene rfaH and the virulence genes kpsM, chuA, and iss were significantly decreased compared to those of the wild-type strain. Macrophage infection assays showed that the mutant strains reduced the replication and/or survival ability in the macrophage HD11 cell line compared to that of the parent strain, E058. However, no significant differences were observed in ingestion by macrophages and in chicken serum resistance between the mutant and the wild-type strains. These data indicate that the tmRNA-SmpB system is important in the pathogenesis of APEC O2 strain E058.