Different activated methyl cycle pathways affect the pathogenicity of avian pathogenic Escherichia coli.

The activated methyl cycle (AMC) regulates the cellular levels of S-adenosyl-l-homocysteine (SAH) in bacteria, which plays a crucial role in bacterial pathogenicity. There are two AMC pathways in bacteria: one is a two-step reaction pathway (named the LuxS/Pfs pathway) in which LuxS and Pfs catalyze the conversion of SAH to l-homocysteine and autoinducer-2 (AI-2), and the other is a one-step reaction (named the SahH pathway) mediated by S-adenosyl-l-homocysteine hydrolase (SahH), which completes this cycle without producing AI-2. In this study, we evaluated the effects of different AMC pathways on the pathogenicity of avian pathogenic Escherichia coli (APEC). The plasmid pSTV-sahH (containing the sahH gene of Pseudomonas aeruginosa) was transformed into the wild-type APEC strain DE17 (containing the LuxS/Pfs pathway) and the pfs mutant strain DE17Δpfs, which lacks the LuxS/Pfs pathway, to create the strains SahH-DE17Δpfs (containing the SahH pathway) and SahH-DE17 (containing the LuxS/Pfs and SahH pathways). The results showed that the different AMC pathways had different effects on the growth rate, AI-2 activity, and motility in APEC. Furthermore, we showed that the 50% lethal doses of the DE17Δpfs and SahH-DE17Δpfs strains were reduced by 650-fold and 52-fold, respectively, in ducklings, compared with that of the DE17 strain. The DE17Δpfs strain exhibited significantly reduced adherence and invasion (p<0.01). In addition, the DE17Δpfs and SahH-DE17Δpfs strains also showed reduced survival in vivo, as evidenced by significant (p<0.01) reductions in their bacterial loads in infected liver, spleen, kidney, and blood. This study suggests that different AMC pathways affect the pathogenesis of APEC.

Xu D ，Zuo J ，Chen Z ，Lv X ，Hu J ，Wu X ，Qi K ，Mi R ，Huang Y ，Miao J ，Jiang W ，Wang S ，Wang C ，Han X ... -  《-》

The luxS gene functions in the pathogenesis of avian pathogenic Escherichia coli.

Avian pathogenic Escherichia coli (APEC) causes avian colibacillosis, the most significant infectious bacterial disease of poultry worldwide. LuxS, the product of the luxS gene, mediates the quorum sensing (QS) mechanism. This involves the production of autoinducer-2 (AI-2), which regulates important physiological traits and a variety of adaptive processes in different bacteria. In this study, a luxS gene deleted APEC mutant strain, ΔDE17, was constructed using strain DE17. Analysis of bioluminescence indicated that deletion of the luxS gene abolished the production of the QS signal AI-2 in the bacteria. Further studies showed that deletion of the luxS gene in DE17 reduced the bacterial virulence by 31.5-fold in ducklings, based on the measurement of the 50% lethal dose. The mutant strain reduced significantly the abilities of adherence and invasion, by 50.0% and 40.7% respectively, compared with the wild strain DE17. The mutant strain also showed reduced survival in vivo: the bacterial loads of the mutant strain in infected liver, spleen and blood were 46.4-fold, 5.2-fold, and 3.7-fold reduced, respectively, compared with the wild-type strain DE17. Real-time polymerase chain reaction (PCR) demonstrated further that the mRNA levels of the virulence-related genes iucD, fyuA, vat, ompA, iss, fimC and tsh were significantly decreased in the mutant strain ΔDE17, when compared with DE17 (p < 0.05). In addition, the deletion of the luxS gene reduced the motility of the bacterium. This study suggests that the luxS gene functions in the pathogenesis of diseases caused by avian pathogenic E. coli.

Han X ，Bai H ，Liu L ，Dong H ，Liu R ，Song J ，Ding C ，Qi K ，Liu H ，Yu S ... -  《-》

Deletion of luxS further attenuates the virulence of the avian pathogenic Escherichia coli aroA mutant.

In this study, an aroA-deletion avian pathogenic Escherichia coli (APEC) mutant (strain DE17ΔaroA) and aroA and luxS double deletion APEC mutant (strain DE17ΔluxSΔaroA) were constructed from the APEC DE17 strain. The results showed that as compared to DE17ΔaroA, the virulence of DE17ΔluxSΔaroA was further attenuated by 200- and 31.7-fold, respectively, in ducklings based on the 50% lethal dose. The adherence and invasion abilities of DE17ΔluxSΔaroA and DE17ΔaroA were reduced by 36.5%/42.5% and 25.8%/29.3%, respectively, as compared to the wild-type strain DE17 (p < 0.05 and 0.01, respectively). Furthermore, in vivo studies showed that the bacterial loads of DE17ΔluxSΔaroA were reduced by 8400- and 11,333-fold in the spleen and blood of infected birds, respectively, while those of DE17ΔaroA were reduced by 743- and 1000-fold, respectively, as compared to the wild-type strain DE17. Histopathological analysis showed both that the mutants were associated with reduced pathological changes in the liver, spleen, and kidney of ducklings, and changes in DE17ΔluxSΔaroA-infected ducklings were reduced to a greater degree than those infected with DE17ΔaroA. Real-time polymerase chain reaction analysis further demonstrated that the mRNA levels of virulence-related genes (i.e., tsh, ompA, vat, iucD, pfs, fyuA, and fimC) were significantly decreased in DE17ΔaroA, especially in DE17ΔluxSΔaroA, as compared to DE17 (p < 0.05). In addition, the deletion of aroA or the double deletion of aroA and luxS reduced bacterial motility. To evaluate the potential use of DE17ΔluxSΔaroA as a vaccine candidate, 50 7-day-old ducklings were divided randomly into five groups of ten each for the experiment. The results showed that the ducklings immunized with inactivated DE17, DE17ΔluxS, DE17ΔaroA, and DE17ΔluxSΔaroA were 70.0%, 70.0%, 70.0, and 80.0% protected, respectively, after challenge with strain APEC DE17. The results of this study suggest that the double deletion of luxS and aroA attenuated APEC pathogenicity and DE17ΔluxSΔaroA was more appropriate for development of a future vaccine against avian colibacillosis than DE17ΔaroA.

Han X ，Bai H ，Tu J ，Yang L ，Xu D ，Wang S ，Qi K ，Fan G ，Zhang Y ，Zuo J ，Tian M ，Ding C ，Yu S ... -  《-》

LuxS contributes to virulence in avian pathogenic Escherichia coli O78:K80:H9.

Avian pathogenic Escherichia coli (APEC) cause avian colibacillosis, a poultry disease characterized by multiple organ infections resulting in significant economic loss in the poultry industry. Several virulence factors are important for disease manifestation in APEC of which, role of quorum sensing has not been investigated. Quorum sensing is a population dependent cell-cell signaling system which modulates numerous physiological processes such as biofilm formation and virulence in multiple species. LuxS, a well-known controller in the QS, plays a role in regulating virulence in various bacterial species. Here we investigated the role of LuxS in regulating virulence in APEC O78:K80:H9. Mutation of luxS resulted in a significant reduction of virulence in APEC O78:K80:H9, evidenced by both in vivo and in vitro assays such as decreased invasion of internal organs in chicken embryo, reduced lethality in chicken embryo lethality assay, and altered lipopolysaccharide (LPS) profile. In addition, the abilities of the knockout strain to survive in chicken macrophage cell lines and to invade in chicken embryo fibroblast cells were significantly diminished. Further, structure and expression level of the LPS profile was significantly altered in the knockout strain, which may be one of the contributing factors for the persistence and virulence of APEC. Complementation of luxS gene in trans restored the virulence of the knockout strain to the level of wild-type bacteria. Taken together, these results show that LuxS contributes to the virulence in APEC O78:K80:H9 strain and partly explain the role played by LuxS in the pathogenesis of APEC strains.

Palaniyandi S ，Mitra A ，Herren CD ，Zhu X ，Mukhopadhyay S ... -  《-》

The role of the ptsI gene on AI-2 internalization and pathogenesis of avian pathogenic Escherichia coli.

The LuxS/AI-2 quorum sensing mechanism can regulate the physiological functions of avian pathogenic Escherichia coli (APEC) through internalization of the small molecule autoinducer-2 (AI-2). The ptsI gene encodes enzyme I, which participates in the phosphotransferase system (PTS) that regulates the virulence and AI-2 internalization of bacteria. The aim of the present study was to determine the effect of ptsI on AI-2 internalization and other pathogenesis process in APEC using a ptsI mutant of the APEC strain DE17 (serotype O2), namely DE17ΔptsI. The results showed that deletion of the ptsI gene changed the rdar (red dry and rough) morphotype and decreased motility and biofilm formation in APEC (p < 0.05). Furthermore, scanning electron microscopy showed that the biofilm structure of DE17ΔptsI became sparse and more extracellular, as compared with the wild-type strain DE17. Moreover, AI-2 assay showed that AI-2 was internalized by DE17ΔptsI, while the recombinant PtsI protein had no AI-2 binding activity. Furthermore, deletion of the ptsI gene in APEC significantly increased adherence to DF-1 cells (p < 0.05). The 50% lethal dose of DE17ΔptsI was decreased by 17.8-fold and the bacterial loads of DE17ΔptsI were decreased by 13600-, 68.5-, 131-, and 3600-fold in the blood, liver, spleen, and kidney, respectively, as compared to the DE17. Moreover, histopathological analysis showed that the mutant DE17ΔptsI was associated with reduced pathological changes in the heart, liver, spleen, and kidney of ducklings, respectively, as compared to the wild-type strain DE17. The results of this study will benefit further studies on the functions of the ptsI in APEC.

Wu X ，Lv X ，Lu J ，Yu S ，Jin Y ，Hu J ，Zuo J ，Mi R ，Huang Y ，Qi K ，Chen Z ，Han X ... -  《-》