Staphylococcus aureus small colony variants impair host immunity by activating host cell glycolysis and inducing necroptosis

Staphylococcus aureus small colony variants (SCVs) are frequently associated with chronic infection, yet they lack expression of many virulence determinants associated with the pathogenicity of wild-type strains. We found that both wild-type S. aureus and a ΔhemB SCV prototype potently activate glycolysis in host cells. Glycolysis and the generation of mitochondrial reactive oxygen species were sufficient to induce necroptosis, a caspase-independent mechanism of host cell death that failed to eradicate S. aureus and instead promoted ΔhemB SCV pathogenicity. To support ongoing glycolytic activity, the ΔhemB SCV induced over a 100-fold increase in the expression of fumC, which encodes an enzyme that catalyses the degradatin of fumarate, an inhibitor of glycolysis. Consistent with fumC-dependent depletion of local fumarate, the ΔhemB SCV failed to elicit trained immunity and protection from a secondary infectious challenge in the skin. The reliance of the S. aureus SCV population on glycolysis accounts for much of its role in the pathogenesis of S. aureus skin infection

Engineering the Controlled Assembly of Filamentous Injectisomes in E. coli K-12 for Protein Translocation into Mammalian Cells.

Bacterial pathogens containing type III protein secretion systems (T3SS) assemble large needle-like protein complexes in the bacterial envelope, called injectisomes, for translocation of protein effectors into host cells. The application of these molecular syringes for the injection of proteins into mammalian cells is hindered by their structural and genomic complexity, requiring multiple polypeptides encoded along with effectors in various transcriptional units (TUs) with intricate regulation. In this work, we have rationally designed the controlled expression of the filamentous injectisomes found in enteropathogenic Escherichia coli (EPEC) in the nonpathogenic strain E. coli K-12. All structural components of EPEC injectisomes, encoded in a genomic island called the locus of enterocyte effacement (LEE), were engineered in five TUs (eLEEs) excluding effectors, promoters and transcriptional regulators. These eLEEs were placed under the control of the IPTG-inducible promoter Ptac and integrated into specific chromosomal sites of E. coli K-12 using a marker-less strategy. The resulting strain, named synthetic injector E. coli (SIEC), assembles filamentous injectisomes similar to those in EPEC. SIEC injectisomes form pores in the host plasma membrane and are able to translocate T3-substrate proteins (e.g., translocated intimin receptor, Tir) into the cytoplasm of HeLa cells reproducing the phenotypes of intimate attachment and polymerization of actin-pedestals elicited by EPEC bacteria. Hence, SIEC strain allows the controlled expression of functional filamentous injectisomes for efficient translocation of proteins with T3S-signals into mammalian cells

The association of RANTES polymorphism with severe acute respiratory syndrome in Hong Kong and Beijing Chinese

<p>Abstract</p> <p>Background</p> <p>Chemokines play important roles in inflammation and antiviral action. We examined whether polymorphisms of <it>RANTES, IP-10 </it>and <it>Mig </it>affect the susceptibility to and outcome of severe acute respiratory syndrome (SARS).</p> <p>Methods</p> <p>We tested the polymorphisms of <it>RANTES, IP-10 </it>and <it>Mig </it>for their associations with SARS in 495 Hong Kong Chinese SARS patients and 578 controls. Then we tried to confirm the results in 356 Beijing Chinese SARS patients and 367 controls.</p> <p>Results</p> <p><it>RANTES </it>-28 G allele was associated with SARS susceptibility in Hong Kong Chinese (<it>P </it>< 0.0001, OR = 2.80, 95%CI:2.11–3.71). Individuals with <it>RANTES </it>-28 CG and GG genotypes had a 3.28-fold (95%CI:2.32–4.64) and 3.06-fold (95%CI:1.47–6.39) increased risk of developing SARS respectively (<it>P </it>< 0.0001). This -28 G allele conferred risk of death in a gene-dosage dependent manner (<it>P </it>= 0.014) with CG and GG individuals having a 2.12-fold (95% CI: 1.11–4.06) and 4.01-fold (95% CI: 1.30–12.4) increased risk. For the replication of <it>RANTES </it>data in Beijing Chinese, the -28 G allele was not associated with susceptibility to SARS. However, -28 CG (OR = 4.27, 95%CI:1.64–11.1) and GG (OR = 3.34, 95%CI:0.37–30.7) were associated with admission to intensive care units or death due to SARS (<it>P </it>= 0.011).</p> <p>Conclusion</p> <p><it>RANTES </it>-28 G allele plays a role in the pathogenesis of SARS.</p

Attaching and effacing (A/E) lesion formation by enteropathogenic E. coli on human intestinal mucosa is dependent on non-LEE effectors

Enteropathogenic E. coli (EPEC) is a human pathogen that causes acute and chronic pediatric diarrhea. The hallmark of EPEC infection is the formation of attaching and effacing (A/E) lesions in the intestinal epithelium. Formation of A/E lesions is mediated by genes located on the pathogenicity island locus of enterocyte effacement (LEE), which encode the adhesin intimin, a type III secretion system (T3SS) and six effectors, including the essential translocated intimin receptor (Tir). Seventeen additional effectors are encoded by genes located outside the LEE, in insertion elements and prophages. Here, using a stepwise approach, we generated an EPEC mutant lacking the entire effector genes (EPEC0) and intermediate mutants. We show that EPEC0 contains a functional T3SS. An EPEC mutant expressing intimin but lacking all the LEE effectors but Tir (EPEC1) was able to trigger robust actin polymerization in HeLa cells and mucin-producing intestinal LS174T cells. However, EPEC1 was unable to form A/E lesions on human intestinal in vitro organ cultures (IVOC). Screening the intermediate mutants for genes involved in A/E lesion formation on IVOC revealed that strains lacking non-LEE effector/s have a marginal ability to form A/E lesions. Furthermore, we found that Efa1/LifA proteins are important for A/E lesion formation efficiency in EPEC strains lacking multiple effectors. Taken together, these results demonstrate the intricate relationships between T3SS effectors and the essential role non-LEE effectors play in A/E lesion formation on mucosal surfaces

Klebsiella pneumoniae induces host metabolic stress that promotes tolerance to pulmonary infection

K. pneumoniae sequence type 258 (Kp ST258) is a major cause of healthcare-associated pneumonia. However, it remains unclear how it causes protracted courses of infection in spite of its expression of immunostimulatory lipopolysaccharide, which should activate a brisk inflammatory response and bacterial clearance. We predicted that the metabolic stress induced by the bacteria in the host cells shapes an immune response that tolerates infection. We combined in situ metabolic imaging and transcriptional analyses to demonstrate that Kp ST258 activates host glutaminolysis and fatty acid oxidation. This response creates an oxidant-rich microenvironment conducive to the accumulation of anti-inflammatory myeloid cells. In this setting, metabolically active Kp ST258 elicits a disease-tolerant immune response. The bacteria, in turn, adapt to airway oxidants by upregulating the type VI secretion system, which is highly conserved across ST258 strains worldwide. Thus, much of the global success of Kp ST258 in hospital settings can be explained by the metabolic activity provoked in the host that promotes disease tolerance. Keywords: immunometabolism, Klebsiella pneumoniae, immunosuppressive, anti-inflammatory, itaconate, Type Six Secretion Syste

Targeted gene sanger sequencing should remain the first-tier genetic test for children suspected to have the five common X-linked inborn errors of immunity

DATA AVAILABILITY STATEMENT : The original contributions presented in the study are included in the article/Supplementary Material. Further inquiries can be directed to the corresponding author.To address inborn errors of immunity (IEI) which were underdiagnosed in resource-limited regions, our centre developed and offered free genetic testing for the most common IEI by Sanger sequencing (SS) since 2001. With the establishment of The Asian Primary Immunodeficiency (APID) Network in 2009, the awareness and definitive diagnosis of IEI were further improved with collaboration among centres caring for IEI patients from East and Southeast Asia. We also started to use whole exome sequencing (WES) for undiagnosed cases and further extended our collaboration with centres from South Asia and Africa. With the increased use of Next Generation Sequencing (NGS), we have shifted our diagnostic practice from SS to WES. However, SS was still one of the key diagnostic tools for IEI for the past two decades. Our centre has performed 2,024 IEI SS genetic tests, with in-house protocol designed specifically for 84 genes, in 1,376 patients with 744 identified to have disease-causing mutations (54.1%). The high diagnostic rate after just one round of targeted gene SS for each of the 5 common IEI (X-linked agammaglobulinemia (XLA) 77.4%, Wiskott–Aldrich syndrome (WAS) 69.2%, X-linked chronic granulomatous disease (XCGD) 59.5%, X-linked severe combined immunodeficiency (XSCID) 51.1%, and X-linked hyper-IgM syndrome (HIGM1) 58.1%) demonstrated targeted gene SS should remain the first-tier genetic test for the 5 common X-linked IEI.The Hong Kong Society for Relief of Disabled Children and Jeffrey Modell Foundation.http://www.frontiersin.org/Immunologyam2023Paediatrics and Child Healt

Characterisation of a family of novel glycosyltransferases from enteropathogenic Escherichia coli and Salmonella

© 2016 Dr. Tania Wong Fok LungEnteropathogenic Escherichia coli (EPEC) is a diarrhoeal pathogen of children that utilises a type III secretion system (T3SS) to inject virulence effector proteins into enterocytes during infection. NleB1 is a novel glycosyltransferase effector from EPEC that catalyses the addition of a single GlcNAc moiety in an N-glycosidic linkage to arginine. NleB1 modifies arginine-117 (Arg117) of the Fas associated death domain (DD) protein, FADD, which prevents assembly of the canonical death inducing signalling complex (DISC) and inhibits FasL-induced cell death. NleB1 also modifies the equivalent arginine residues in the DD proteins, tumour necrosis factor receptor type 1 (TNFR1)-associated death domain (TRADD) and receptor-interacting protein kinase 1 (RIPK1). Apart from the DxD catalytic motif of NleB1, little is known about other functional sites in the protein and the regions required for substrate binding and specificity. Here a library of 22 random transposon-based, in-frame, linker insertion mutants of NleB1 were tested for their ability to block caspase-8 activation in response to FasL during EPEC infection. Immunoblot analysis of caspase-8 cleavage products showed that 14 mutant derivatives of NleB1 no longer inhibited caspase-8 activation, including the catalytic DxD mutant. Regions of interest around the linker insertion sites were examined further with multiple or single amino acid substitutions. Coimmunoprecipitation studies of 34 site-directed mutants showed that the NleB1 derivatives with the E253A, Y219A, and PILN(63– 66)AAAA (in which the PILN motif from residues 63 to 66 was changed to AAAA) mutations bound to but did not GlcNAcylate FADD. A further mutant derivative, the PDG(236 –238)AAA mutant, did not bind to or GlcNAcylate FADD. Further testing of these mutants with TRADD and RIPK1, showed that NleB1 bearing the mutations E253A and Y219A could still bind to FADD and RIPK1 but not to TRADD. Infection of mice with the EPEC-like mouse pathogen Citrobacter rodentium expressing NleBE253A and NleBY219A showed that these 2 strains were attenuated, indicating the importance of the residues E253 and Y219 in NleB1 virulence in vivo. In summary, we identified new amino acid residues critical for NleB1 activity and confirmed that FADD GlcNAcylation was critical for NleB1 function. Close homologues of NleB1 are found in Salmonella enterica serovar Typhimurium and these are termed SseK1, SseK2 and SseK3. We hypothesized that the SseK effectors would also bind to DD proteins and inhibit apoptotic or inflammatory signalling. The SseK effectors did not appear to play a strong role in the inhibition of death receptor signaling given that we could not detect binding of the SseK effectors to the death domain proteins FADD, TRADD and RIPK1, which are targets of NleB1. A further survey of DD proteins revealed that SseK3 bound to TNFR1. However S. Typhimurium did not appear to inhibit TNF-induced IL-8 production and the biological significance of this interaction is still unknown. We conclude that the SseKs have an alternative function during S. Typhimurium infection to NleB1 in EPEC

p53 mutations in non-small cell lung carcinomas in Hong Kong

Lung resections from 50 Chinese patients in Hong Kong diagnosed as having non-small cell lung carcinoma were examined for the presence of mutations in the p53 gene by polymerase chain reaction single-stranded conformation polymorphism methods and for aberrant protein expression by immunostaining techniques. Eight-point mutations in the evolutionarily conserved exon 5 through 8 regions were detected. Abnormal expression of p53 detectable by immunostaining techniques was seen in 23 specimens tested. There was no statistically significant correlation between the detection of p53 aberrations and age, sex, smoking history, histologic type, and tumor stage. Aberrant p53 protein levels detectable by immunostaining were significantly associated with the clinical and nodal staging of the tumors

p53 mutational spectrum of esophageal carcinomas from five different geographical locales in China

A mutational spectrum for exons 5-8 of the p53 tumor suppressor gene in esophageal carcinomas in mainland China and Hong Kong was established, This study involved 209 squamous cell carcinoma specimens obtained from five different geographical locales in China: Zhengzhou, Taiyuan, Shantou, Guangzhou, and Hong Kong. Zhengzhou and Shantou were high-incidence regions for esophageal cancer, whereas the other three regions had low or intermediate incidence of the disease, Analysis by single-strand conformation polymorphism and DNA sequencing showed that 87 specimens (41.6\%) contained mutations in exons 5-8 of the p53 gene compared to 163 cases (78\%) that had accumulation or aberrant expression of the protein, as detected by immunohistochemical staining, Point mutations accounted for 80.4\% (87/107) of all genetic changes, The specimens from northern China exhibited fewer p53 gene aberrations and a more even distribution of mutations in exons 5-8 compared to those from southern China in which 60\% of all mutations were found in exon 5, A major hot spot was found at codon 176 in exon 5, where 41 samples from Shantou, Guangzhou, and Hong Kong had a G --> T transversion, It is likely that among southern Chinese this codon is susceptible to mutagenesis by carcinogens, Codons 175, 203, 245, 250, 273, and 282 were also shown to be mutational hot spots, with three or more mutations observed at each site, The p53 mutational data obtained in this study showed that Chinese esophageal carcinomas are often associated with some unique genetic alterations, which may be attributed to specific dietary or environmental carcinogens that affect the Chinese but not Caucasians