Chlamydial Plasmid-Dependent Pathogenicity

Design of a novel multi-epitope vaccine candidate against Chlamydia trachomatis using structural and nonstructural proteins: an immunoinformatics study

Chlamydia trachomatis (C. trachomatis) is an obligate intracellular bacterium which causes eye and sexually transmitted infections. During pregnancy, the bacterium is associated with preterm complications, low weight of neonates, fetal demise and endometritis leading to infertility. The aim of our study was design of a multi-epitope vaccine (MEV) candidate against C. trachomatis. After protein sequence adoption from the NCBI, potential epitopes toxicity, antigenicity, allergenicity, MHC-I and MHC-II binding, cytotoxic T lymphocytes (CTLs), Helper T lymphocytes (HTLs) and interferon-γ (IFN-γ)- induction were predicted. The adopted epitopes were fused together using appropriate linkers. In the next step, the MEV structural mapping and characterization, three-dimensional (3D) structure homology modeling and refinement were also performed. The MEV candidate interaction with the toll-like receptor 4 (TLR4) was also docked. The immune responses simulation was assessed using the C-IMMSIM server. Molecular dynamic (MD) simulation verified the structural stability of the TLR4-MEV complex. The Molecular Mechanics Poisson-Boltzmann Surface Area (MMPBSA) approach demonstrated the MEV high affinity of binding to the TLR4, MHC-I and MHC-II. The MEV construct was also stable and water soluble and had enough antigenicity and lacked allergenicity with stimulation of T cells and B cells and INF-γ release. The immune simulation confirmed acceptable responses of both the humoral and cellular arms. It is proposed that in vitro and in vivo studies are needed to evaluate the findings of this study.Communicated by Ramaswamy H. Sarma.

Validation of a New Duplex Real-Time Polymerase Chain Reaction for Chlamydia trachomatis DNA Detection in Ocular Swab Samples

Trachoma is the world-leading infectious cause of preventable blindness and is caused by the bacteria Chlamydia trachomatis. In developing countries, diagnosis is usually based on clinical evaluation. Serological-based tests are cheaper than molecular-based ones, but the latter are more sensitive and specific. The present study developed a new duplex qPCR which concomitantly detects the C. trachomatis cryptic plasmid and the human 18S rRNA gene, with an LOD95% for C. trachomatis DNA of 13.04 genome equivalents per reaction. The new qPCR was tested using 50 samples from an endemic area and 12 from a non-endemic area that were previously characterized using direct immunofluorescence assay (DFA) and clinical evaluation. Among the 50 endemic samples, 3 were found to be positive by clinical evaluation (6%), 18 were found to be positive by DFA (36%), and 48 were found to be positive by qPCR (96%). Next, the new duplex qPCR was validated using 50 samples previously characterized by qPCR. Validation was carried out on a benchtop instrument (ABI7500) or on a portable point-of-care instrument (Q3-Plus), showing 95% specificity and 100% sensitivity. The ubiquitous presence of C. trachomatis DNA in samples from the endemic region confirms that constant monitoring is of paramount importance for the effective measurement of the elimination of trachoma. The newly developed duplex qPCR presented in this study, along with its validation in a portable qPCR system, constitutes important tools toward achieving this goal.

Antibody responses to Chlamydia trachomatis vaccine candidate antigens in Chlamydia-infected women and correlation with antibody-mediated phagocytosis of elementary bodies

Murine research has revealed a significant role for antibody responses in protection against Chlamydia reinfection. To explore potential humoral immune markers of protection elicited by Chlamydia trachomatis (CT) antigens in humans in the context of presumed clinical correlates of protection, we used both an IgG1-based ELISA and a conventional total IgG ELISA to evaluate antibody responses. We evaluated responses to five CT outer membrane proteins (PmpE, PmpF, PmpG, PmpH, and MOMP), along with other promising CT antigens (Pgp3 and HSP60), negative control antigens (RecO and AtpE), and CT elementary bodies (EBs) in sera from a well-characterized cohort of 60 women with different CT infection outcomes, including two outcomes that are likely clinical correlates of protective immunity: spontaneous resolution of infection and absence of reinfection after treatment. Furthermore, we used a flow cytometry-based assay to measure antibody-mediated phagocytosis by neutrophils in these sera. Results demonstrated that IgG1 ELISA displayed higher sensitivity than conventional total IgG ELISA in assessing antibody responses to CT EBs and antigens. Pgp3 IgG1 ELISA exhibited the highest sensitivity compared to IgG1 ELISA incorporating CT EBs or other antigens, confirming Pgp3 IgG1 ELISA as an ideal assay for CT antibody detection. Most (95%) sera from women with CT infection outcomes exhibited antibody-mediated phagocytosis of CT EBs, which was significantly correlated with IgG1 antibody responses to MOMP, Pgp3, HSP60, and PmpF. However, neither IgG1 responses to CT antigens and EBs nor antibody-mediated phagocytosis were associated with clinical correlates of protection. These findings suggest that neither CT IgG1 antibody detection nor antibody-mediated phagocytosis will be useful as immune correlates of protection against CT infection in humans.

Regulation of chlamydial spreading from the small intestine to the large intestine by IL-22-producing CD4+ T cells

Following an oral inoculation, Chlamydia muridarum descends to the mouse large intestine for long-lasting colonization. However, a mutant C. muridarum that lacks the plasmid-encoded protein pGP3 due to an engineered premature stop codon (designated as CMpGP3S) failed to do so even following an intrajejunal inoculation. This was because a CD4+ T cell-dependent immunity prevented the spread of CMpGP3S from the small intestine to the large intestine. In the current study, we found that mice deficient in IL-22 (IL-22-/-) allowed CMpGP3S to spread from the small intestine to the large intestine on day 3 after intrajejunal inoculation, indicating a critical role of IL-22 in regulating the chlamydial spread. The responsible IL-22 is produced by CD4+ T cells since IL-22-/- mice were rescued to block the CMpGP3S spread by donor CD4+ T cells from C57BL/6J mice. Consistently, CD4+ T cells lacking IL-22 failed to block the spread of CMpGP3S in Rag2-/- mice, while IL-22-competent CD4+ T cells did block. Furthermore, mice deficient in cathelicidin-related antimicrobial peptide (CRAMP) permitted the CMpGP3S spread, but donor CD4+ T cells from CRAMP-/- mice were still sufficient for preventing the CMpGP3S spread in Rag2-/- mice, indicating a critical role of CRAMP in regulating chlamydial spreading, and the responsible CRAMP is not produced by CD4+ T cells. Thus, the IL-22-producing CD4+ T cell-dependent regulation of chlamydial spreading correlated with CRAMP produced by non-CD4+ T cells. These findings provide a platform for further characterizing the subset(s) of CD4+ T cells responsible for regulating bacterial spreading in the intestine.

Requirement of GrgA for Chlamydia infectious progeny production, optimal growth, and efficient plasmid maintenance

IMPORTANCE

Hallmarks of the developmental cycle of the obligate intracellular pathogenic bacterium Chlamydia are the primary differentiation of the infectious elementary body (EB) into the proliferative reticulate body (RB) and the secondary differentiation of RBs back into EBs. The mechanisms regulating these transitions remain unclear. In this report, we developed an effective novel strategy termed dependence on plasmid-mediated expression (DOPE) that allows for the knockdown of essential genes in Chlamydia. We demonstrate that GrgA, a Chlamydia-specific transcription factor, is essential for the secondary differentiation and optimal growth of RBs. We also show that GrgA, a chromosome-encoded regulatory protein, controls the maintenance of the chlamydial virulence plasmid. Transcriptomic analysis further indicates that GrgA functions as a critical regulator of all three sigma factors that recognize different promoter sets at developmental stages. The DOPE strategy outlined here should provide a valuable tool for future studies examining chlamydial growth, development, and pathogenicity.

Preclinical screen for protection efficacy of chlamydial antigens that are immunogenic in humans

To search for subunit vaccine candidates, immunogenic chlamydial antigens identified in humans were evaluated for protection against both infection and pathology in a mouse genital tract infection model under three different immunization regimens. The intramuscular immunization regimen was first used to evaluate 106 chlamydial antigens, which revealed that two antigens significantly reduced while 11 increased genital chlamydial burden. The two infection-reducing antigens failed to prevent pathology and 23 additional antigens even exacerbated pathology. Thus, intranasal mucosal immunization was tested next since intranasal inoculation with live Chlamydia muridarum prevented both genital infection and pathology. Two of the 29 chlamydial antigens evaluated were found to prevent genital infection but not pathology and three exacerbate pathology. To further improve protection efficacy, a combinational regimen (intranasal priming + intramuscular boosting + a third intraperitoneal/subcutaneous boost) was tested. This regimen identified four infection-reducing antigens, but only one of them prevented pathology. Unfortunately, this protective antigen was not advanced further due to its amino acid sequence homology with several human molecules. Two pathology-exacerbating antigens were also found. Nevertheless, intranasal mucosal priming with viable C. muridarum in control groups consistently prevented both genital infection and pathology regardless of the subsequent boosters. Thus, screening 140 different chlamydial antigens with 21 repeated multiple times in 17 experiments failed to identify a subunit vaccine candidate but demonstrated the superiority of viable chlamydial organisms in inducing immunity against both genital infection and pathology, laying the foundation for developing a live-attenuated Chlamydia vaccine.

Molecular pathogenesis of Chlamydia trachomatis

Chlamydia trachomatis is a strict intracellular human pathogen. It is the main bacterial cause of sexually transmitted infections and the etiologic agent of trachoma, which is the leading cause of preventable blindness. Despite over 100 years since C. trachomatis was first identified, there is still no vaccine. However in recent years, the advancement of genetic manipulation approaches for C. trachomatis has increased our understanding of the molecular pathogenesis of C. trachomatis and progress towards a vaccine. In this mini-review, we aimed to outline the factors related to the developmental cycle phase and specific pathogenesis activity of C. trachomatis in order to focus priorities for future genetic approaches. We highlight the factors known to be critical for developmental cycle stages, gene expression regulatory factors, type III secretion system and their effectors, and individual virulence factors with known impacts.

Requirement of GrgA for Chlamydia infectious progeny production, optimal growth, and efficient plasmid maintenance

Chlamydia, an obligate intracellular bacterial pathogen, has a unique developmental cycle involving the differentiation of invading elementary bodies (EBs) to noninfectious reticulate bodies (RBs), replication of RBs, and redifferentiation of RBs into progeny EBs. Progression of this cycle is regulated by three sigma factors, which direct the RNA polymerase to their respective target gene promoters. We hypothesized that the Chlamydia-specific transcriptional regulator GrgA, previously shown to activate σ66 and σ28, plays an essential role in chlamydial development and growth. To test this hypothesis, we applied a novel genetic tool known as dependence on plasmid-mediated expression (DOPE) to create Chlamydia trachomatis with conditional GrgA-deficiency. We show that GrgA-deficient C. trachomatis RBs have a growth rate that is approximately half of the normal rate and fail to transition into progeny EBs. In addition, GrgA-deficient C. trachomatis fail to maintain its virulence plasmid. Results of RNA-seq analysis indicate that GrgA promotes RB growth by optimizing tRNA synthesis and expression of nutrient-acquisition genes, while it enables RB-to-EB conversion by facilitating the expression of a histone and outer membrane proteins required for EB morphogenesis. GrgA also regulates numerous other late genes required for host cell exit and subsequent EB invasion into host cells. Importantly, GrgA stimulates the expression of σ54, the third and last sigma factor, and its activator AtoC, and thereby indirectly upregulating the expression of σ54-dependent genes. In conclusion, our work demonstrates that GrgA is a master transcriptional regulator in Chlamydia and plays multiple essential roles in chlamydial pathogenicity.

Tryptophan residue of plasmid-encoded Pgp3 is important for Chlamydia muridarum to induce hydrosalpinx in mice

The crucial role of plasmid-encoded protein Pgp3 in Chlamydia pathogenesis has been demonstrated in various animal models. Previous studies have revealed that the Pgp3-deficient C. muridarum mutant fails to induce hydrosalpinx after vaginal inoculation in mice. Structural analysis of C. trachomatis Pgp3 trimer has indicated that Trp234 may play a critical role in trimeric crystal packing interactions and that Tyr197 is involved at predominant cation-binding sites. In this study, we constructed C. muridarum transformants harboring Pgp3, Trp234, or Tyr197 point mutations (Pgp3W234A and Pgp3Y197A). C3H/HeJ mice infected with Pgp3W234A mutant failed to induce severe hydrosalpinx in the oviduct tissue, which largely phenocopied the full-length Pgp3-deficient C. muridarum. The Pgp3Y197A variant induced an intermediate severity of pathology. The attenuated pathogenicity caused by the Pgp3W234A mutant may be due to its decreased survival in the lower genital tracts of mice, reduced ascension to the oviduct, and milder induction of inflammatory cell infiltration in the oviduct tissue. Thus, our results point to an important amino acid residue involved in Pgp3 virulence, providing a potential therapeutic target for chlamydial infection.

An Overview of Selected Bacterial Infections in Cancer, Their Virulence Factors, and Some Aspects of Infection Management

In cancer development and its clinical course, bacteria can be involved in etiology and secondary infection. Regarding etiology, various epidemiological studies have revealed that Helicobacter pylori can directly impact gastric carcinogenesis. The Helicobacter pylori-associated virulence factor cytotoxin-associated gene A perhaps plays an important role through different mechanisms such as aberrant DNA methylation, activation of nuclear factor kappa B, and modulation of the Wnt/β-catenin signaling pathway. Many other bacteria, including Salmonella and Pseudomonas, can also affect Wnt/β-catenin signaling. Although Helicobacter pylori is involved in both gastric adenocarcinoma and mucosa-associated lymphoid tissue lymphoma, its role in the latter disease is more complicated. Among other bacterial species, Chlamydia is linked with a diverse range of diseases including cancers of different sites. The cellular organizations of Chlamydia are highly complex. Interestingly, Escherichia coli is believed to be associated with colon cancer development. Microorganisms such as Escherichia coli and Pseudomonas aeruginosa are frequently isolated from secondary infections in cancer patients. In these patients, the common sites of infection are the respiratory, gastrointestinal, and urinary tracts. There is an alarming rise in infections with multidrug-resistant bacteria and the scarcity of suitable antimicrobial agents adversely influences prognosis. Therefore, effective implementation of antimicrobial stewardship strategies is important in cancer patients.

Genome organization and genomics in Chlamydia: whole genome sequencing increases understanding of chlamydial virulence, evolution, and phylogeny

The genus Chlamydia contains important obligate intracellular bacterial pathogens to humans and animals, including C. trachomatis and C. pneumoniae. Since 1998, when the first Chlamydia genome was published, our understanding of how these microbes interact, evolved and adapted to different intracellular host environments has been transformed due to the expansion of chlamydial genomes. This review explores the current state of knowledge in Chlamydia genomics and how whole genome sequencing has revolutionised our understanding of Chlamydia virulence, evolution, and phylogeny over the past two and a half decades. This review will also highlight developments in multi-omics and other approaches that have complemented whole genome sequencing to advance knowledge of Chlamydia pathogenesis and future directions for chlamydial genomics.

Chlamydia trachomatis-An Emerging Old Entity?

Chlamydia trachomatis is an evasive pathogen that can prompt severe clinical manifestations in humans such as vaginitis, epididymitis, lymphogranuloma venereum, trachoma, conjunctivitis and pneumonia. If left untreated, chronic infections with C. trachomatis can give rise to long-lasting and even permanent sequelae. To shed some light on its widespread nature, data from original research, systematic reviews and meta-analyses from three databases was collected and analyzed in the context of chlamydial infection, related symptoms and appropriate treatment modalities. This review describes the bacterium's pervasiveness on a global scale, especially in developing countries, and suggests ways to halt its transmission and spread. Infections with C. trachomatis often go unnoticed, as many individuals are asymptomatic and unaware of their diagnosis, contributing to a delay in diagnosis and treatment. The high prevalence of chlamydial infection highlights the need for a universal screening and detection method enabling immediate treatment at its onset. Prognosis is favorable with antibiotic therapy and education for high-risk groups and their sexual partners. In the future, a quick, easily accessible, and inexpensive test should be developed to diagnose and treat infected individuals early on. Along with a vaccine against C. trachomatis, it would halt the transmission and spread of the pathogen worldwide.

Molecular characterisation of the Australian and New Zealand livestock Chlamydia pecorum strains confirms novel but clonal ST23 in association with ovine foetal loss

Chlamydia pecorum is a veterinary pathogen associated with abortions and perinatal mortality in sheep. Recent studies investigating foetal and perinatal lamb mortality in sheep from Australia and New Zealand identified C. pecorum clonal sequence type (ST)23 strains in aborted and stillborn lambs. Presently, there is limited genotypic information on C. pecorum strains associated with reproductive disease, although whole genome sequencing (WGS) of one abortigenic ST23 C. pecorum strain identified unique features, including a deletion in the CDS1 locus of the chlamydial plasmid. We applied WGS on two ST23 strains detected in aborted and stillborn lambs from Australia and used phylogenetic and comparative analyses to compare these to the other available C. pecorum genomes. To re-evaluate the genetic diversity of contemporary strains, we applied C. pecorum genotyping, and chlamydial plasmid sequencing to a range of C. pecorum positive samples and isolates from ewes, aborted foetuses and stillborn lambs, cattle and a goat from diverse geographical regions across Australia and New Zealand.The two new C. pecorum genomes are nearly identical to the genome of the Australian abortigenic strain including the unique deletion in the chlamydial plasmid. Genotyping revealed that these novel C. pecorum ST23 strains are widespread and associated with sheep abortions on Australian and New Zealand farms. In addition, a goat C. pecorum strain (denoted ST 304) from New Zealand was also characterised. This study expands the C. pecorum genome catalogue and describes a comprehensive molecular characterisation of the novel livestock ST23 strains associated with foetal and lamb mortality.

Protective Immunity against Chlamydia psittaci Lung Infection Induced by a DNA Plasmid Vaccine Carrying CPSIT_p7 Gene Inhibits Dissemination in BALB/c Mice

Chlamydia psittaci (C. psittaci), a zoonotic pathogen, poses a potential threat to public health security and the development of animal husbandry. Vaccine-based preventative measures for infectious diseases have a promising landscape. DNA vaccines, with many advantages, have become one of the dominant candidate strategies in preventing and controlling the chlamydial infection. Our previous study showed that CPSIT_p7 protein is an effective candidate for a vaccine against C. psittaci. Thus, this study evaluated the protective immunity of pcDNA3.1(+)/CPSIT_p7 against C. psittaci infection in BALB/c mice. We found that pcDNA3.1(+)/CPSIT_p7 can induce strong humoral and cellular immune responses. The IFN-γ and IL-6 levels in the infected lungs of mice immunized with pcDNA3.1(+)/CPSIT_p7 reduced substantially. In addition, the pcDNA3.1(+)/CPSIT_p7 vaccine diminished pulmonary pathological lesions and reduced the C. psittaci load in the lungs of infected mice. It is worth noting that pcDNA3.1(+)/CPSIT_p7 suppressed C. psittaci dissemination in BALB/c mice. In a word, these results demonstrate that the pcDNA3.1(+)/CPSIT_p7 DNA vaccine has good immunogenicity and immunity protection effectiveness against C. psittaci infection in BALB/c mice, especially pulmonary infection, and provides essential practical experience and insights for the development of a DNA vaccine against chlamydial infection.

Pgp3 protein of Chlamydia trachomatis inhibits apoptosis via HO-1 upregulation mediated by PI3K/Akt activation

As an obligate intracellular pathogen, Chlamydia trachomatis assumes various strategies to inhibit host cells apoptosis, thereby providing a suitable intracellular environment to ensure completion of the development cycle. In the current study, we revealed that Pgp3 protein, one of eight plasmid proteins of C. trachomatis that has been illustrated as the key virulence factor, increased HO-1 expression to suppress apoptosis, and downregulation of HO-1 with siRNA-HO-1 failed to exert anti-apoptosis activity of Pgp3 protein. Moreover, treatment of PI3K/Akt pathway inhibitor and Nrf2 inhibitor evidently reduced HO-1 expression and Nrf2 nuclear translocation was blocked by PI3K/Akt pathway inhibitor. These findings highlight that induction of HO-1 expression by Pgp3 protein is probably due to regulation of Nrf2 nuclear translocation activated by PI3K/Akt pathway, which provide clues on how C. trachomatis adjusts apoptosis.

Regulation of chlamydial colonization by IFNγ delivered via distinct cells

The mouse-adapted pathogen Chlamydia muridarum (CM) induces pathology in the mouse genital tract but fails to do so in the gastrointestinal tract. CM is cleared from both the genital tract and small intestine by IFNγ delivered by antigen-specific CD4+ T cells but persists for a long period in the large intestine. The long-lasting colonization of CM in the large intestine is regulated by IFNγ delivered by group 3 innate lymphoid cells (ILC3s). Interestingly, the ILC3-delivered IFNγ can inhibit the human pathogen Chlamydia trachomatis (CT) in the mouse endometrium. Thus, IFNγ produced/delivered by different cells may selectively restrict chlamydial colonization in different tissues. Revealing the underlying mechanisms of chlamydial interactions with IFNγ produced by different cells may yield new insights into both chlamydial pathogenicity and mucosal immunity.

Gut dysbiosis contributes to chlamydial induction of hydrosalpinx in the upper genital tract

Chlamydia trachomatis is one of the most common sexually infections that cause infertility, and its genital infection induces tubal adhesion and hydrosalpinx. Intravaginal Chlamydia muridarum infection in mice can induce hydrosalpinx in the upper genital tract and it has been used for studying C. trachomatis pathogenicity. DBA2/J strain mice were known to be resistant to the chlamydial induction of hydrosalpinx. In this study, we took advantage of this feature of DBA2/J mice to evaluate the role of antibiotic induced dysbiosis in chlamydial pathogenicity. Antibiotics (vancomycin and gentamicin) were orally administrated to induce dysbiosis in the gut of DBA2/J mice. The mice with or without antibiotic treatment were evaluated for gut and genital dysbiosis and then intravaginally challenged by C. muridarum. Chlamydial burden was tested and genital pathologies were evaluated. We found that oral antibiotics significantly enhanced chlamydial induction of genital hydrosalpinx. And the antibiotic treatment induced severe dysbiosis in the GI tract, including significantly reduced fecal DNA and increased ratios of firmicutes over bacteroidetes. The oral antibiotic did not alter chlamydial infection or microbiota in the mouse genital tracts. Our study showed that the oral antibiotics-enhanced hydrosalpinx correlated with dysbiosis in gut, providing the evidence for associating gut microbiome with chlamydial genital pathogenicity.

Alternative strategies for Chlamydia treatment: Promising non-antibiotic approaches

Chlamydia is an obligate intracellular bacterium where most species are pathogenic and infectious, causing various infectious diseases and complications in humans and animals. Antibiotics are often recommended for the clinical treatment of chlamydial infections. However, extensive research has shown that antibiotics may not be sufficient to eliminate or inhibit infection entirely and have some potential risks, including antibiotic resistance. The impact of chlamydial infection and antibiotic misuse should not be underestimated in public health. This study explores the possibility of new therapeutic techniques, including a review of recent studies on preventing and suppressing chlamydial infection by non-antibiotic compounds.

Chlamydia transmitting from the genital to gastrointestinal tract and inducing tubal disease: Double attack pattern

Chlamydia trachomatis ( CT ) genital tract infection is insidious, and patients often have no conscious symptoms.Delayed treatment after infection can lead to serious complications. Chlamydia muridarum ( CM ) genital tract infection in female mice can simulate CT genital tract infection in women, which is an ideal model to investigate the pathogenesis of CT . CM plasmid protein pGP3, chromosomal protein TC0237/TC0668, CM -specific CD8 + T cells, TNF-α, and IL-13 can induce genital tract inflammation, CD4 + T cells are responsible for CM clearance. However, tubal inflammation persists after genital tract CM is removed. Genital tract CM can spread spontaneously in vivo and colonize the gastrointestinal (GI) tract, but the GI tract CM cannot reverse spread to the genital tract. The survival time and number of CM transmitted from genital tract to GI tract are positively correlated with the long-term lesion of oviduct, while the CM inoculated directly into the GI tract has no pathogenicity in both the genital and GI tract. The double attack pattern of Chlamydia -induced genital tract inflammatory lesions is as follows: CM infection of oviduct epithelial cells initiates the process of oviduct repair as the first attack. After genital CM spreads to the GI tract, activated chlamydia-specific CD8 + T cells are recruited to the genital tract and secreted pro-fibrotic cytokines such as TNF-α and IL-13. This process is called the second attack which transform tubal repair initiated by the first attack into long-term tubal fibrosis/hydrosalpinx. Elucidating the pathogenic mechanism of Chlamydia infection can provide new ideas for the development of Chlamydia vaccine, which is expected to solve the problems of infertility caused by repeated CT infection in women.

The Type III Secretion Effector CteG Mediates Host Cell Lytic Exit of Chlamydia trachomatis

Chlamydia trachomatis is an obligate intracellular bacterium causing ocular and urogenital infections in humans that are a significant burden worldwide. The completion of its characteristic infectious cycle relies on the manipulation of several host cell processes by numerous chlamydial type III secretion effector proteins. We previously identified the C. trachomatis CteG effector and showed it localizes at the host cell plasma membrane at late stages of infection. Here, we showed that, from 48 h post-infection, mammalian cells infected by wild-type C. trachomatis contained more infectious chlamydiae in the culture supernatant than cells infected by a CteG-deficient strain. This phenotype was CteG-dependent as it could be complemented in cells infected by the CteG-deficient strain carrying a plasmid encoding CteG. Furthermore, we detected a CteG-dependent defect on host cell cytotoxicity, indicating that CteG mediates chlamydial lytic exit. Previous studies showed that Pgp4, a global regulator of transcription encoded in the C. trachomatis virulence plasmid, also mediates chlamydial lytic exit. However, by using C. trachomatis strains encoding or lacking Pgp4, we showed that production and localization of CteG are not regulated by Pgp4. A C. trachomatis strain lacking both CteG and Pgp4 was as defective in promoting host cell cytotoxicity as mutant strains lacking only CteG or Pgp4. Furthermore, CteG overproduction in a plasmid suppressed the host cell cytotoxic defect of CteG- and Pgp4-deficient chlamydiae. Overall, we revealed the first chlamydial type III secretion effector involved in host cell lytic exit. Our data indicates that CteG and Pgp4 participate in a single cascade of events, but involving multiple layers of regulation, leading to lysis of host cells and release of the infectious chlamydiae.

Ecology and evolution of chlamydial symbionts of arthropods

The phylum Chlamydiae consists of obligate intracellular bacteria including major human pathogens and diverse environmental representatives. Here we investigated the Rhabdochlamydiaceae, which is predicted to be the largest and most diverse chlamydial family, with the few described members known to infect arthropod hosts. Using published 16 S rRNA gene sequence data we identified at least 388 genus-level lineages containing about 14 051 putative species within this family. We show that rhabdochlamydiae are mainly found in freshwater and soil environments, suggesting the existence of diverse, yet unknown hosts. Next, we used a comprehensive genome dataset including metagenome assembled genomes classified as members of the family Rhabdochlamydiaceae, and we added novel complete genome sequences of Rhabdochlamydia porcellionis infecting the woodlouse Porcellio scaber, and of 'Candidatus R. oedothoracis' associated with the linyphiid dwarf spider Oedothorax gibbosus. Comparative analysis of basic genome features and gene content with reference genomes of well-studied chlamydial families with known host ranges, namely Parachlamydiaceae (protist hosts) and Chlamydiaceae (human and other vertebrate hosts) suggested distinct niches for members of the Rhabdochlamydiaceae. We propose that members of the family represent intermediate stages of adaptation of chlamydiae from protists to vertebrate hosts. Within the genus Rhabdochlamydia, pronounced genome size reduction could be observed (1.49-1.93 Mb). The abundance and genomic distribution of transposases suggests transposable element expansion and subsequent gene inactivation as a mechanism of genome streamlining during adaptation to new hosts. This type of genome reduction has never been described before for any member of the phylum Chlamydiae. This study provides new insights into the molecular ecology, genomic diversity, and evolution of representatives of one of the most divergent chlamydial families.

Chlamydia deficient in plasmid-encoded glycoprotein 3 (pGP3) as an attenuated live oral vaccine

Despite the extensive efforts, there is still a lack of a licensed vaccine against Chlamydia trachomatis in humans. The mouse genital tract infection with Chlamydia muridarum has been used to both investigate chlamydial pathogenic mechanisms and evaluate vaccine candidates due to the C. muridarum’s ability to induce mouse hydrosalpinx. C. muridarum mutants lacking the entire plasmid or deficient in only the plasmid-encoded pGP3 are highly attenuated in inducing hydrosalpinx. We now report that intravaginal immunization with these mutants as live attenuated vaccines protected mice from hydrosalpinx induced by wild type C. muridarum . However, these mutants still productively infected the mouse genital tract. Further, the mutant-infected mice were only partially protected against the subsequent infection with wild type C. muridarum . Thus, these mutants as vaccines are neither safe nor effective when they are delivered via the genital tract. Interestingly, these mutants were highly deficient in colonizing the gastrointestinal tract. Particularly, the pGP3-deficient mutant failed to shed live organisms from mice following an oral inoculation, suggesting that the pGP3-deficient mutant may be developed into a safe oral vaccine. Indeed, oral inoculation with the pGP3-deficient mutant induced robust transmucosal immunity against both the infection and pathogenicity of wild type C. muridarum in the genital tract. Thus, we have demonstrated that the plasmid-encoded virulence factor pGP3 may be targeted for developing an attenuated live oral vaccine.

Robust Heat Shock Response in Chlamydia Lacking a Typical Heat Shock Sigma Factor

Cells reprogram their transcriptome in response to stress, such as heat shock. In free-living bacteria, the transcriptomic reprogramming is mediated by increased DNA-binding activity of heat shock sigma factors and activation of genes normally repressed by heat-induced transcription factors. In this study, we performed transcriptomic analyses to investigate heat shock response in the obligate intracellular bacterium Chlamydia trachomatis, whose genome encodes only three sigma factors and a single heat-induced transcription factor. Nearly one-third of C. trachomatis genes showed statistically significant (≥1.5-fold) expression changes 30 min after shifting from 37 to 45°C. Notably, chromosomal genes encoding chaperones, energy metabolism enzymes, type III secretion proteins, as well as most plasmid-encoded genes, were differentially upregulated. In contrast, genes with functions in protein synthesis were disproportionately downregulated. These findings suggest that facilitating protein folding, increasing energy production, manipulating host activities, upregulating plasmid-encoded gene expression, and decreasing general protein synthesis helps facilitate C. trachomatis survival under stress. In addition to relieving negative regulation by the heat-inducible transcriptional repressor HrcA, heat shock upregulated the chlamydial primary sigma factor σ⁶⁶ and an alternative sigma factor σ²⁸. Interestingly, we show for the first time that heat shock downregulates the other alternative sigma factor σ⁵⁴ in a bacterium. Downregulation of σ⁵⁴ was accompanied by increased expression of the σ⁵⁴ RNA polymerase activator AtoC, thus suggesting a unique regulatory mechanism for reestablishing normal expression of select σ⁵⁴ target genes. Taken together, our findings reveal that C. trachomatis utilizes multiple novel survival strategies to cope with environmental stress and even to replicate. Future strategies that can specifically target and disrupt Chlamydia’s heat shock response will likely be of therapeutic value.

Why do plasmids manipulate the expression of bacterial phenotypes?

Conjugative plasmids play an important role in bacterial evolution by transferring niche-adaptive traits between lineages, thus driving adaptation and genome diversification. It is increasingly clear, however, that in addition to this evolutionary role, plasmids also manipulate the expression of a broad range of bacterial phenotypes. In this review, we argue that the effects that plasmids have on the expression of bacterial phenotypes may often represent plasmid adaptations, rather than mere deleterious side effects. We begin by summarizing findings from untargeted omics analyses, which give a picture of the global effects of plasmid acquisition on host cells. Thereafter, because many plasmids are capable of both vertical and horizontal transmission, we distinguish plasmid-mediated phenotypic effects into two main classes based upon their potential fitness benefit to plasmids: (i) those that promote the competitiveness of the host cell in a given niche and thereby increase plasmid vertical transmission, and (ii) those that promote plasmid conjugation and thereby increase plasmid horizontal transmission. Far from being mere vehicles for gene exchange, we propose that plasmids often act as sophisticated genetic parasites capable of manipulating their bacterial hosts for their own benefit.

This article is part of the theme issue ‘The secret lives of microbial mobile genetic elements’.

Mycoplasma decontamination in Chlamydia trachomatis culture: a curative approach

Mycoplasma contamination of cell culture represents a serious problem in research and decontamination from cell-propagated obligate intracellular bacteria has proven challenging. Here, we presented an optimized protocol to remove Mycoplasma from contaminated Chlamydia trachomatis culture. A stepwise procedure of Mycoplasma removal entails (i) incubation in nonionic detergent containing solution, and (ii) separation of viable chlamydial organisms by fluorescence-activated cell sorting (FACS), followed by subcloning using a focus-forming assay. We also adapted a polymerase chain reaction (PCR) assay using paired universal and Mycoplasma-specific primers, which are distinguishable from the C. trachomatis counterparts, in combination with Sanger sequencing to determine the presence of mycoplasmas' 16S rRNA genes. These integrated approaches allow for full removal of Mycoplasma, as verified by the improved PCR assay, without compromising the capacity of viable C. trachomatis to adapt to new infection in epithelial cells. Some pitfalls during the Mycoplasma decontamination process are discussed.

Characterization of pathogenic CD8+ T cells in Chlamydia-infected OT1 mice

Chlamydia trachomatis is a leading infectious cause of infertility in women due to its induction of lasting pathology such as hydrosalpinx. Chlamydia muridarum induces mouse hydrosalpinx because C. muridarum can both invade tubal epithelia directly (as a 1^st hit) and induce lymphocytes to promote hydrosalpinx indirectly (as a 2^nd hit). In the current study, a critical role of CD8⁺ T cells in chlamydial induction of hydrosalpinx was validated in both wild type C57BL/6J and OT1 transgenic mice. OT1 mice failed to develop hydrosalpinx partially due to the failure of their lymphocytes to recognize chlamydial antigens. CD8⁺ T cells from naïve C57BL/6J rescued the recipient OT1 mice to develop hydrosalpinx when naïve CD8⁺ T cells were transferred at the time of infection with Chlamydia. However, when the transfer was delayed for 2 weeks or longer after the chlamydial infection, naïve CD8⁺ T cells no longer promoted hydrosalpinx. Nevertheless, Chlamydia-immunized CD8⁺ T cells still promoted significant hydrosalpinx in the recipient OT1 mice even when the transfer was delayed for 3 weeks. Thus, CD8⁺ T cells must be primed within 2 weeks after chlamydial infection to be pathogenic but once primed, they can promote hydrosalpinx for >3 weeks. However, Chlamydia-primed CD4⁺ T cells failed to promote chlamydial induction of pathology in OT1 mice. This study has optimized an OT1 mouse-based model for revealing the pathogenic mechanisms of Chlamydia-specific CD8⁺ T cells.

Chlamydia spreads to the large intestine lumen via multiple pathways

Chlamydia in the genital tract is known to spread via the blood circulation system to the large intestinal lumen to achieve long-lasting colonization. However, the precise pathways for genital Chlamydia to access to the large intestinal lumen remain unclear. The spleen was recently reported to be critical for the chlamydial spreading. In the current study, it was found that following intravaginal inoculation with Chlamydia, mice with or without splenectomy both produced infectious Chlamydia in the rectal swabs, indicating that spleen is not essential for genital Chlamydia to spread to the gastrointestinal tract. This conclusion was validated by the observation that intravenously inoculated Chlamydia was also detected in the rectal swabs of mice regardless of splenectomy. Careful comparison of the tissue distribution of live chlamydial organisms following intravenous inoculation revealed redundant pathways for Chlamydia to reach the large intestine lumen. The intravenously inoculated Chlamydia was predominantly recruited to the spleen within 12h and then detected in the stomach lumen by 24h, the intestinal lumen by 48h and rectal swabs by 72h. These observations suggest a potential spleen-to-stomach pathway for hematogenous Chlamydia to reach the large intestine lumen. This conclusion was supported by the observation made in mice under coprophagy-free condition. However, in the absence of spleen, hematogenous Chlamydia was predominantly recruited to the liver and then simultaneously detected in the intestinal tissue and lumen, suggesting a potential liver-to-intestine pathway for Chlamydia to reach the large intestine lumen. Thus, genital/hematogenous Chlamydia may reach the large intestinal lumen via multiple redundant pathways.

Gastrointestinal Chlamydia-induced CD8+ T cells promote chlamydial pathogenicity in the female upper genital tract

Chlamydia is known to both ascend to the upper genital tract and spread to the gastrointestinal tract following intravaginal inoculation. The gastrointestinal Chlamydia was recently reported to promote chlamydial pathogenicity in the genital tract since mice intravaginally inoculated with an attenuated Chlamydia, which alone failed to develop pathology in the genital tract, were restored to develop hydrosalpinx by intragastric co-inoculation with wild type Chlamydia. Gastrointestinal Chlamydia promoted hydrosalpinx via an indirect mechanism since Chlamydia in the gut did not directly spread to the genital tract lumen. In the current study, we further investigated the role of CD8⁺ T cells in the promotion of hydrosalpinx by gastrointestinal Chlamydia. First, we confirmed that intragastric co-inoculation with wild type Chlamydia promoted hydrosalpinx in mice that were inoculated with an attenuated Chlamydia in the genital tract one week earlier. Second, the promotion of hydrosalpinx by intragastrically co-inoculated Chlamydia was blocked by depleting CD8⁺ T cells. Third, adoptive transfer of the gastrointestinal Chlamydia-induced CD8⁺ T cells was sufficient for promoting hydrosalpinx in mice that were intravaginally inoculated with an attenuated Chlamydia. These observations have demonstrated that CD8⁺ T cells induced by gastrointestinal Chlamydia are both necessary and sufficient for promoting hydrosalpinx in the genital tract. The study has laid a foundation for further revealing the mechanisms by which Chlamydia-induced T lymphocyte responses (as a 2^nd hit) promote hydrosalpinx in mice with genital Chlamydia-triggered tubal injury (as a 1^st hit), a continuing effort in testing the two-hit hypothesis as a chlamydial pathogenic mechanism.

The growing repertoire of genetic tools for dissecting chlamydial pathogenesis

Multiple species of obligate intracellular bacteria in the genus Chlamydia are important veterinary and/or human pathogens. These pathogens all share similar biphasic developmental cycles and transition between intracellular vegetative reticulate bodies and infectious elementary forms, but vary substantially in their host preferences and pathogenic potential. A lack of tools for genetic engineering of these organisms has long been an impediment to the study of their biology and pathogenesis. However, the refinement of approaches developed in C. trachomatis over the last 10 years, and adaptation of some of these approaches to other Chlamydia spp. in just the last few years, has opened exciting new possibilities for studying this ubiquitous group of important pathogens.

Chlamydia trachomatis Pgp3 protein regulates oxidative stress via activation of the Nrf2/NQO1 signal pathway

AIM

Chlamydia trachomatis has evolved various strategies to alleviate oxidative stress of host cells to maintain their intracellular survival. However, the exact mechanism of anti-oxidative stress of C. trachomatis is still unclear. The activation of nuclear factor erythroid 2-related factor 2/quinone oxidoreductase (Nrf2/NQO1) signal pathway has been identified as an efficient antioxidant defensive mechanism used by host cells to counteract oxidative stress. Pgp3 is a pivotal virulence factor of C. trachomatis involved in intracellular survival. The aim of this study is to explore the role of Pgp3 on Nrf2/NQO1 signal pathway against oxidative stress.

MAIN METHODS

After HeLa cells were stimulated with Pgp3 protein, Nrf2 location and the inclusion bodies of C. trachomatis were detected by indirect immunofluorescence, western blotting and Oxidative stress assay kits were used to separately determine the protein expression and the content of malondialdehyde (MDA), superoxide dismutase (SOD) and total antioxidant capacity (T-AOC) before and after the interference of Nrf-2 and NQO1.

KEY FINDINGS

Pgp3 promoted the nuclear translocation of Nrf2 to increase NQO1 expression and reduced oxidative stress induced by LPS to contribute to the survival of C. trachomatis. Inhibition of Nrf2/NQO1 signal pathway with Nrf2 inhibitor and down-regulation of NQO1 with siRNA-NQO1 suppressed oxidative stress resistance induced by Pgp3.

SIGNIFICANCE

Here we found that Pgp3 alleviated oxidative stress to promote the infectivity of C. trachomatis through activation of Nrf2/NQO1 signal pathway, which provided a novel understanding of the effects of Pgp3 in the pathogenesis of C. trachomatis.

Chlamydia overcomes multiple gastrointestinal barriers to achieve long-lasting colonization

Chlamydia trachomatis (CT) is frequently detected in the human gastrointestinal (GI) tract despite its leading role in sexually transmitted bacterial infections in the genital tract. Chlamydia muridarum (CM), a model pathogen for investigating CT pathogenesis in the genital tract, can also colonize the mouse GI tract for long periods. Genital-tract mutants of CM no longer colonize the GI tract. The mutants lacking plasmid functions are more defective in colonizing the upper GI tract while certain chromosomal gene-deficient mutants are more defective in the lower GI tract, suggesting that Chlamydia may use the plasmid for promoting its spread to the large intestine while using the chromosome-encoded factors for maintaining its colonization in the large intestine. The plasmid-encoded Pgp3 is critical for Chlamydia to resist the acid barrier in the stomach and to overcome a CD4⁺ T cell barrier in the small intestine. On reaching the large intestine, Pgp3 is no longer required. Instead, the chromosome-encoded open reading frames TC0237/TC0668 become essential for Chlamydia to evade the group 3-like innate lymphoid cell-secreted interferon (IFN)γ in the large intestine. These findings are important for exploring the medical significance of chlamydial colonization in the gut and for understanding the mechanisms of chlamydial pathogenicity in the genital tract.

Regulation of the Mitochondrion-Fatty Acid Axis for the Metabolic Reprogramming of Chlamydia trachomatis during Treatment with β-Lactam Antimicrobials

Infection with the obligate intracellular bacterium Chlamydia trachomatis is the most common bacterial sexually transmitted disease worldwide. Since no vaccine is available to date, antimicrobial therapy is the only alternative in C. trachomatis infection. However, changes in chlamydial replicative activity and the occurrence of chlamydial persistence caused by diverse stimuli have been proven to impair treatment effectiveness. Here, we report the mechanism for C. trachomatis regulating host signaling processes and mitochondrial function, which can be used for chlamydial metabolic reprogramming during treatment with β-lactam antimicrobials. Activation of signal transducer and activator of transcription 3 (STAT3) is a well-known host response in various bacterial and viral infections. In C. trachomatis infection, inactivation of STAT3 by host protein tyrosine phosphatases increased mitochondrial respiration in both the absence and presence of β-lactam antimicrobials. However, during treatment with β-lactam antimicrobials, C. trachomatis increased the production of citrate as well as the activity of host ATP-citrate lyase involved in fatty acid synthesis. Concomitantly, chlamydial metabolism switched from the tricarboxylic acid cycle to fatty acid synthesis. This metabolic switch was a unique response in treatment with β-lactam antimicrobials and was not observed in gamma interferon (IFN-γ)-induced persistent infection. Inhibition of fatty acid synthesis was able to attenuate β-lactam-induced chlamydial persistence. Our findings highlight the importance of the mitochondrion-fatty acid interplay for the metabolic reprogramming of C. trachomatis during treatment with β-lactam antimicrobials.IMPORTANCE The mitochondrion generates most of the ATP in eukaryotic cells, and its activity is used for controlling the intracellular growth of Chlamydia trachomatis Furthermore, mitochondrial activity is tightly connected to host fatty acid synthesis that is indispensable for chlamydial membrane biogenesis. Phospholipids, which are composed of fatty acids, are the central components of the bacterial membrane and play a crucial role in the protection against antimicrobials. Chlamydial persistence that is induced by various stimuli is clinically relevant. While one of the well-recognized inducers, β-lactam antimicrobials, has been used to characterize chlamydial persistence, little is known about the role of mitochondria in persistent infection. Here, we demonstrate how C. trachomatis undergoes metabolic reprogramming to switch from the tricarboxylic acid cycle to fatty acid synthesis with promoted host mitochondrial activity in response to treatment with β-lactam antimicrobials.

Regulation of Chlamydia spreading from the small intestine to the large intestine via an immunological barrier

The obligate intracellular bacterium Chlamydia is a genital tract pathogen that can also colonize the gastrointestinal tract for long periods. The long-lasting colonization is dependent on chlamydial spreading from the small intestine to the large intestine. We previously reported that a mutant Chlamydia was able to activate an intestinal barrier for blocking its own spreading to the large intestine. In the current study, we used the mutant Chlamydia colonization model to confirm the intestinal barrier function and further to determine the immunological basis of the barrier with gene-deficient mice. Recombination activating gene 1^-/- mice failed to block the mutant Chlamydia spreading, while mice deficient in toll-like receptors, myeloid differentiation primary response 88 or stimulator of interferon genes still blocked the spreading, suggesting that the intestinal barrier function is dependent on lymphocytes that express antigen receptors. Mice deficient in CD4, but not CD8 nor μ chain failed to prevent the chlamydial spreading, indicating a protective role of CD4⁺ cells in the intestinal barrier. Consistently, adoptive transfer of CD4⁺ T cells reconstituted the intestinal barrier in CD4^-/- mice. More importantly, CD4⁺ but not CD8⁺ T cells nor B cells restored the intestinal barrier function in recombination activating gene 1^-/- mice. Thus, CD4⁺ T cells are necessary and sufficient for maintaining the intestinal barrier function, indicating that the spread of an intracellular bacterium from the small intestine to the large intestine is regulated by an immunological barrier. This study has also laid a foundation for further illuminating the mechanisms by which a CD4⁺ T cell-dependent intestinal barrier regulates bacterial spreading in the gut.

Coevolving Plasmids Drive Gene Flow and Genome Plasticity in Host-Associated Intracellular Bacteria

Plasmids are important in microbial evolution and adaptation to new environments. Yet, carrying a plasmid can be costly, and long-term association of plasmids with their hosts is poorly understood. Here, we provide evidence that the Chlamydiae, a phylum of strictly host-associated intracellular bacteria, have coevolved with their plasmids since their last common ancestor. Current chlamydial plasmids are amalgamations of at least one ancestral plasmid and a bacteriophage. We show that the majority of plasmid genes are also found on chromosomes of extant chlamydiae. The most conserved plasmid gene families are predominantly vertically inherited, while accessory plasmid gene families show significantly increased mobility. We reconstructed the evolutionary history of plasmid gene content of an entire bacterial phylum over a period of around one billion years. Frequent horizontal gene transfer and chromosomal integration events illustrate the pronounced impact of coevolution with these extrachromosomal elements on bacterial genome dynamics in host-dependent microbes.

Chlamydia psittaci Plasmid-Encoded CPSIT_P7 Elicits Inflammatory Response in Human Monocytes via TLR4/Mal/MyD88/NF-κB Signaling Pathway

The chlamydial plasmid, an essential virulence factor, encodes plasmid proteins that play important roles in chlamydial infection and the corresponding immune response. However, the virulence factors and the molecular mechanisms of Chlamydia psittaci are not well understood. In the present study, we investigated the roles and mechanisms of the plasmid-encoded protein CPSIT_P7 of C. psittaci in regulating the inflammatory response in THP-1 cells (human monocytic leukemia cell line). Based on cytokine arrays, CPSIT_P7 induces the expression of interleukin-6 (IL-6), interleukin-8 (IL-8), and monocyte chemoattractant protein-1 (MCP-1) in THP-1 cells. Moreover, the expression levels of IL-6, IL-8, and MCP-1 stimulated by CPSIT_P7 declined after silencing of the Toll-like receptor 4 (TLR4) gene using small interfering RNA and transfection of a dominant negative plasmid encoding TLR4 (pZERO-hTLR4). We further demonstrated that transfection with the dominant negative plasmid encoding MyD88 (pDeNy-hMyD88) and the dominant negative plasmid encoding Mal (pDeNy-hMal) could also abrogate the expression of the corresponding proteins. Western blot and immunofluorescence assay results showed that CPSIT_P7 could activate nuclear factor κB (NF-κB) signaling pathways in THP-1 cells. Altogether, our results indicate that the CPSIT_P7 induces the TLR4/Mal/MyD88/NF-κB signaling axis and therefore contributes to the inflammatory cytokine response.

Effects of Immunomodulatory Drug Fingolimod (FTY720) on Chlamydia Dissemination and Pathogenesis

Fingolimod (FTY720), an FDA-approved immunomodulatory drug for treating multiple sclerosis, is an agonist of sphingosine-1-phosphate receptor (S1PR), which has been used as a research tool for inhibiting immune cell trafficking. FTY720 was recently reported to inhibit Chlamydia dissemination. Since genital Chlamydia spreading to the gastrointestinal tract correlated with its pathogenicity in the upper genital tract, we evaluated the effect of FTY720 on chlamydial pathogenicity in the current study. Following an intravaginal inoculation, live chlamydial organisms were detected in mouse rectal swabs. FTY720 treatment significantly delayed live organism shedding in the rectal swabs. However, FTY720 failed to block chlamydial spreading to the gastrointestinal tract. The live chlamydial organisms recovered from rectal swabs reached similar levels between mice with or without FTY720 treatment by day 42 in C57BL/6J and day 28 in CBA/J mice, respectively. Thus, genital Chlamydia is able to launch a 2nd wave of spreading via an FTY720-resistant pathway after the 1st wave of spreading is inhibited by FTY720. As a result, all mice developed significant hydrosalpinx. The FTY720-resistant spreading led to stable colonization of chlamydial organisms in the colon. Consistently, FTY720 did not alter the colonization of intracolonically inoculated Chlamydia Thus, we have demonstrated that, following a delay in chlamydial spreading caused by FTY720, genital Chlamydia is able to both spread to the gastrointestinal tract via an FTY720-resistant pathway and maintain its pathogenicity in the upper genital tract. Further characterization of the FTY720-resistant pathway(s) explored by Chlamydia for spreading to the gastrointestinal tract may promote our understanding of Chlamydia pathogenic mechanisms.

Suppression of Chlamydial Pathogenicity by Nonspecific CD8+ T Lymphocytes

Chlamydia trachomatis, a leading infectious cause of tubal infertility, induces upper genital tract pathology, such as hydrosalpinx, which can be modeled with Chlamydia muridarum infection in mice. Following C. muridarum inoculation, wild-type mice develop robust hydrosalpinx, but OT1 mice fail to do so because their T cell receptors are engineered to recognize a single ovalbumin epitope (OVA457-462). These observations have demonstrated a critical role of Chlamydia-specific T cells in chlamydial pathogenicity. In the current study, we have also found that OT1 mice can actively inhibit chlamydial pathogenicity. First, depletion of CD8+ T cells from OT1 mice led to the induction of significant hydrosalpinx by Chlamydia, indicating that CD8+ T cells are necessary to inhibit chlamydial pathogenicity. Second, adoptive transfer of CD8+ T cells from OT1 mice to CD8 knockout mice significantly reduced chlamydial induction of hydrosalpinx, demonstrating that OT1 CD8+ T cells are sufficient for attenuating chlamydial pathogenicity in CD8 knockout mice. Finally, CD8+ T cells from OT1 mice also significantly inhibited hydrosalpinx development in wild-type mice following an intravaginal inoculation with Chlamydia Since T cells in OT1 mice are engineered to recognize only the OVA457-462 epitope, the above observations have demonstrated a chlamydial antigen-independent immune mechanism for regulating chlamydial pathogenicity. Further characterization of this mechanism may provide information for developing strategies to reduce infertility-causing pathology induced by infections.

Chlamydia Deficient in Plasmid-Encoded pGP3 Is Prevented from Spreading to Large Intestine

The cryptic plasmid pCM is critical for chlamydial colonization in the gastrointestinal tract. Nevertheless, orally inoculated plasmid-free Chlamydia sp. was still able to colonize the gut. Surprisingly, orally inoculated Chlamydia sp. deficient in only plasmid-encoded pGP3 was no longer able to colonize the gut. A comparison of live organism recoveries from individual gastrointestinal tissues revealed that pGP3-deficient Chlamydia sp. survived significantly better than plasmid-free Chlamydia sp. in small intestinal tissues. However, the small intestinal pGP3-deficient Chlamydia sp. failed to reach the large intestine, explaining the lack of live pGP3-deficient Chlamydia sp. in rectal swabs following an oral inoculation. Interestingly, pGP3-deficient Chlamydia sp. was able to colonize the colon following an intracolon inoculation, suggesting that pGP3-deficient Chlamydia sp. might be prevented from spreading from the small intestine to the large intestine. This hypothesis is supported by the finding that following an intrajejunal inoculation that bypasses the gastric barrier, pGP3-deficient Chlamydia sp. still failed to reach the large intestine, although similarly inoculated plasmid-free Chlamydia sp. was able to do so. Interestingly, when both types of organisms were intrajejunally coinoculated into the same mouse small intestine, plasmid-free Chlamydia sp. was no longer able to spread to the large intestine, suggesting that pGP3-deficient Chlamydia sp. might be able to activate an intestinal resistance for regulating Chlamydia sp. spreading. Thus, the current study has not only provided evidence for reconciling a previously identified conflicting phenotype but also revealed a potential intestinal resistance to chlamydial spreading. Efforts are under way to further define the mechanism of the putative intestinal resistance.

The Repressor Function of the Chlamydia Late Regulator EUO Is Enhanced by the Plasmid-Encoded Protein Pgp4

A critical step in intracellular Chlamydia infection is the production of infectious progeny through the expression of late genes. This differentiation step involves conversion from a reticulate body (RB), which is the replicating form of the bacterium, into an elementary body (EB), which is the developmental form that spreads the infection to a new host cell. EUO is an important chlamydial transcription factor that controls the expression of late genes, but the mechanisms that regulate EUO are not known. We report that a plasmid-encoded protein, Pgp4, enhanced the repressor activity of EUO. Pgp4 did not function as a transcription factor because it did not bind or directly modulate transcription of its target promoters. Instead, Pgp4 increased the ability of EUO to bind and repress EUO-regulated promoters in vitro and physically interacted with EUO in pulldown assays with recombinant proteins. We detected earlier onset of EUO-dependent late gene expression by immunofluorescence microscopy in Pgp4-deficient C. trachomatis and C. muridarum strains. In addition, the absence of Pgp4 led to earlier onset of RB-to-EB conversion in C. muridarum These data support a role for Pgp4 as a negative regulator of chlamydial transcription that delays late gene expression. Our studies revealed that Pgp4 also has an EUO-independent function as a positive regulator of chlamydial transcription.IMPORTANCE Chlamydia trachomatis is an important human pathogen that causes more than 150 million active cases of genital and eye infection in the world. This obligate intracellular bacterium produces infectious progeny within an infected human cell through the expression of late chlamydial genes. We showed that the ability of a key chlamydial transcription factor, EUO, to repress late genes was enhanced by a plasmid-encoded protein, Pgp4. In addition, studies with Chlamydia Pgp4-deficient strains provide evidence that Pgp4 delays late gene expression in infected cells. Thus, Pgp4 is a novel regulator of late gene expression in Chlamydia through its ability to enhance the repressor function of EUO.

Analysis of COMPASS, a New Comprehensive Plasmid Database Revealed Prevalence of Multireplicon and Extensive Diversity of IncF Plasmids

Plasmids are genetic elements that enable rapid adaptation and evolution by transferring genes conferring selective advantages to their hosts. Conjugative plasmids are predominantly responsible for the global dissemination of antimicrobial resistance, representing an important threat to global health. As the number of plasmid sequences grows exponentially, it becomes critical to depict the global diversity and decipher the distribution of circulating plasmids in the bacterial community. To this end, we created COMPASS, a novel and comprehensive database compiling 12,084 complete plasmids with associated metadata from 1571 distinct species isolated worldwide over more than 100 years. The curation of the database allowed us to identify identical plasmids across different bacteria revealing mainly intraspecies dissemination and rare cases of horizontal transmission. We outlined and analyzed all relevant features, plasmid properties, host range and characterized their replication and mobilization systems. After an exhaustive comparison of PlasmidFinder and MOB-typer, the MOB-typer-based analysis revealed that the current knowledge embedded in the current typing schemes fails to classify all the plasmid sequences collected in COMPASS. We were able to categorize 6828 and 5229 plasmids by replicon and MOB typing, respectively, mostly associated with Proteobacteria and Firmicutes. We then searched for the presence of multiple core genes involved in replication and propagation. Our results showed that 2403 plasmids carried multiple replicons that were distributed in 206 bacterial species. The co-integration of replicon types from different incompatibility (Inc) groups is an adaptive mechanism, which plays an important role in plasmid survival and dissemination by extending their host range. Our results highlight the crucial role of IncF alleles (present in 56% of all multireplicons) and revealed that IncH, IncR, and IncU replicons were also frequently carried in multireplicons. Here, we provided a comprehensive picture of the different IncF subtypes by identifying 20 different profiles in 849 IncF multireplicons, which were mostly associated with Enterobacteriaceae. These results could provide the basis for a novel IncF plasmid nomenclature based on different allelic profiles.

Gastrointestinal Coinfection Promotes Chlamydial Pathogenicity in the Genital Tract

Sexually transmitted Chlamydia, which can cause fibrotic pathology in women's genital tracts, is also frequently detected in the gastrointestinal tract. However, the medical significance of the gastrointestinal Chlamydia remains unclear. A murine Chlamydia readily spreads from the mouse genital tract to the gastrointestinal tract while inducing oviduct fibrotic blockage or hydrosalpinx. We previously proposed a two-hit model in which the mouse gastrointestinal Chlamydia might induce the second hit to promote genital tract pathology, and we are now providing experimental evidence for testing the hypothesis. First, chlamydial mutants that are attenuated in inducing hydrosalpinx in the genital tract also reduce their colonization in the gastrointestinal tract, leading to a better correlation of chlamydial induction of hydrosalpinx with chlamydial colonization in the gastrointestinal tract than in the genital tract. Second, intragastric coinoculation with a wild-type Chlamydia rescued an attenuated Chlamydia mutant to induce hydrosalpinx, while the chlamydial mutant infection in the genital tract alone was unable to induce any significant hydrosalpinx. Finally, the coinoculated gastrointestinal Chlamydia failed to directly spread to the genital tract lumen, suggesting that gastrointestinal Chlamydia may promote genital pathology via an indirect mechanism. Thus, we have demonstrated a significant role of gastrointestinal Chlamydia in promoting pathology in the genital tract possibly via an indirect mechanism. This study provides a novel direction/dimension for further investigating chlamydial pathogenic mechanisms.

The Cryptic Plasmid Improves Chlamydia Fitness in Different Regions of the Gastrointestinal Tract

The cryptic plasmid is important for chlamydial colonization in the gastrointestinal tract. We used a combination of intragastric, intrajejunal, and intracolon inoculations to reveal the impact of the plasmid on chlamydial colonization in distinct regions of gastrointestinal tract. Following an intragastric inoculation, the plasmid significantly improved chlamydial colonization. At the tissue level, plasmid-positive Chlamydia produced infectious progenies throughout gastrointestinal tract. However, to our surprise, plasmid-deficient Chlamydia failed to produce infectious progenies in small intestine, although infectious progenies were eventually detected in large intestine, indicating a critical role of the plasmid in chlamydial differentiation into infectious particles in small intestine. The noninfectious status may represent persistent infection, since Chlamydia genomes proliferated in the same tissues. Following an intrajejunal inoculation that bypasses the gastric barrier, plasmid-deficient Chlamydia produced infectious progenies in small intestine but was 530-fold less infectious than plasmid-positive Chlamydia, suggesting that (i) the noninfectious status developed after intragastric inoculation might be induced by a combination of gastric and intestinal effectors and (ii) chlamydial colonization in small intestine was highly dependent on plasmid. Finally, following an intracolon inoculation, the dependence of chlamydial colonization on plasmid increased over time. Thus, we have demonstrated that the plasmid may be able to improve chlamydial fitness in different gut regions via different mechanisms, which has laid a foundation to further reveal the specific mechanisms.

Identification of HeLa cell proteins that interact with Chlamydia trachomatis glycogen synthase using yeast two‑hybrid assays

Chlamydia trachomatis (C. trachomatis) is the leading cause of bacterial sexually transmitted diseases and infectious diseases that cause blindness. The pathophysiology of chlamydial infections is poorly understood, but secreted proteins have emerged as key virulence factors. C. trachomatis glycogen synthase (GlgA) is a chlamydial secretory protein, which localizes in the lumen of chlamydial inclusion bodies and the cytosol of host cells. In order to improve understanding of the roles of GlgA in chlamydial pathogenesis, four proteins that interact with GlgA, Homo sapiens CXXC finger protein 1, prohibitin (PHB), gelsolin-like actin-capping protein and apolipoprotein A-I binding protein were identified using yeast two-hybrid assays. The functions of these proteins are complex, and preliminary results suggested that PHB interacts with GlgA. However, further studies are required to determine the specific interactions of these proteins with GlgA. The findings of the present study may provide a direction and foundation for future studies focusing on the mechanism of GlgA in C. trachomatis infection.

Rapid and accurate diagnosis of Chlamydia trachomatis in the urogenital tract by a dual-gene multiplex qPCR method

Introduction. Chlamydia trachomatis (C. trachomatis, CT) is an obligatory intracellular bacterium that causes urogenital tract infections and leads to severe reproductive consequences. Therefore, a rapid and accurate detection method with high sensitivity and specificity is an urgent requirement for the routine diagnosis of C. trachomatis infections.Aim. In this study, we aimed to develop a multiplex quantitative real-time PCR (qPCR) assay based on two target regions for accurate detection of C. trachomatis in urogenital tract infections.Methodology. Primers and probes based on the conserved regions of the cryptic plasmid and 23S rRNA gene were designed. Then, two qPCR assays were established to screen for the optimal probe and primers for each of the two target regions. Subsequently, the multiplex qPCR method was developed and optimized. For the diagnostic efficiency evaluation, 1284 urogenital specimens were tested by the newly developed multiplex qPCR method, an immunological assay and a singleplex qPCR assay widely used in hospitals.Results. The multiplex qPCR method could amplify both target regions in the range of 1.0×10²-1.0×10⁸ copies ml^-1 with a strong linear relationship, and lower limits of detection (LODs) for both targets reached 2 copies PCR^-1. For the multiplex qPCR method, the diagnostic sensitivity and specificity was 100.0 % (134/134) and 99.3 % (1142/1150), respectively. For the singleplex qPCR assay, the diagnostic sensitivity and specificity was 88.8 % (119/134) and 100.0 % (1150/1150), respectively. For the immunological assay, the diagnostic sensitivity and specificity was 47.0 % (63/134) and 100.0 % (1150/1150), respectively.Conclusion. In this study, a multiplex qPCR assay with high sensitivity and specificity for rapid (≤2.0 h) and accurate diagnosis of C. trachomatis was developed. The qPCR assay has the potential to be used as a routine diagnostic method in clinical microbiology laboratories.

The multiple functions of the numerous Chlamydia trachomatis secreted proteins: the tip of the iceberg

Chlamydia trachomatis serovars are obligate intracellular bacterial pathogens mainly causing ocular and urogenital infections that affect millions of people worldwide and which can lead to blindness or sterility. They reside and multiply intracellularly within a membrane-bound vacuolar compartment, known as inclusion, and are characterized by a developmental cycle involving two morphologically and physiologically distinct chlamydial forms. Completion of the developmental cycle involves the secretion of > 70 C. trachomatis proteins that function in the host cell cytoplasm and nucleus, in the inclusion membrane and lumen, and in the extracellular milieu. These proteins can, for example, interfere with the host cell cytoskeleton, vesicular and non-vesicular transport, metabolism, and immune signalling. Generally, this promotes C. trachomatis invasion into, and escape from, host cells, the acquisition of nutrients by the chlamydiae, and evasion of cell-autonomous, humoral and cellular innate immunity. Here, we present an in-depth review on the current knowledge and outstanding questions about these C. trachomatis secreted proteins.

Distinct Roles of Chromosome- versus Plasmid-Encoded Genital Tract Virulence Factors in Promoting Chlamydia muridarum Colonization in the Gastrointestinal Tract

The genital pathogen Chlamydia is known to colonize the gastrointestinal tract. Orally delivered Chlamydia muridarum can reach the colon and maintain a long-lasting colonization there. However, C. muridarum with mutations in chromosomal genes tc0237 and tc0668 (designated a chromosomal mutant) or deficient in plasmid-encoded pGP3 (designated a plasmid mutant) is unable to do so. We now report that the chromosomal mutant is still able to reach the colon while the plasmid mutant fails to do so following an oral delivery, suggesting that lack of colon colonization by different mutants may involve distinct mechanisms. Consistently, a direct intracolonic delivery selectively restored the ability of the plasmid mutant, but not the chromosomal mutant, to colonize the colon. The chromosomal mutant was rescued only in the colon of mice deficient in gamma interferon (IFN-γ). Thus, the chromosomal mutant's deficiency in colonizing colonic mucosal tissue is likely due to its increased susceptibility to IFN-γ-mediated immunity. Furthermore, IFN-γ deficiency was sufficient for rescuing colon colonization of an orally delivered chromosomal mutant but not plasmid mutant while mice deficient in gastric acid production rescued the plasmid mutant but not the chromosomal mutant. Both mutants are attenuated in inducing genital tract pathology. Thus, we propose that chlamydial chromosomal-gene-encoded genital tract virulence factors may be essential for Chlamydia to maintain long-lasting colonization in the colon while the plasmid may enable Chlamydia to reach the colon by promoting evasion of gastric barriers.

Chlamydia muridarum Induces Pathology in the Female Upper Genital Tract via Distinct Mechanisms

Sexually transmitted infection with Chlamydia trachomatis may lead to fibrotic blockage in women's upper genital tracts, resulting in tubal infertility. Intravaginal inoculation with C. muridarum readily induces fibrotic blockage or hydrosalpinx in mice and is used for investigating C. trachomatis pathogenicity. Using this model in combination with an antibody depletion approach, we confirmed CD4⁺ T cell-mediated protective immunity and a CD8⁺ T cell-dependent pathogenic mechanism during chlamydial infection in C57BL/6J mice. However, when mice genetically deficient in CD8⁺ T cells were evaluated, we found, surprisingly, that these mice were still able to develop robust hydrosalpinx following C. muridarum infection, both contradicting the observation made in C57BL/6J mice and suggesting a pathogenic mechanism that is independent of CD8⁺ T cells. We further found that depletion of CD4⁺ T cells from CD8⁺ T cell-deficient mice significantly reduced chlamydial induction of hydrosalpinx, indicating that CD4⁺ T cells became pathogenic in mice genetically deficient in CD8⁺ T cells. Since depletion of CD4⁺ T cells both promoted chlamydial infection and reduced chlamydial pathogenicity in CD8⁺ T cell-deficient mice, we propose that in the absence of CD8⁺ T cells, some CD4⁺ T cells may remain protective (as in C57BL/6J mice), while others may directly contribute to chlamydial pathogenicity. Thus, chlamydial pathogenicity can be mediated by distinct host mechanisms, depending upon host genetics and infection conditions. The CD8⁺ T cell-deficient mouse model may be useful for further investigating the mechanisms by which CD4⁺ T cells promote chlamydial pathogenicity.

Clear Victory for Chlamydia: The Subversion of Host Innate Immunity

As obligate intracellular bacterial pathogens, members of the Chlamydia genera are the pivotal triggers for a wide range of infections, which can lead to blinding trachoma, pelvic inflammation, and respiratory diseases. Because of their restricted parasitism inside eukaryotic cells, the pathogens have to develop multiple strategies for adaptation with the hostile intracellular environment—intrinsically present in all host cells—to survive. The strategies that are brought into play at different stages of chlamydial development mainly involve interfering with diverse innate immune responses, such as innate immune recognition, inflammation, apoptosis, autophagy, as well as the manipulation of innate immune cells to serve as potential niches for chlamydial replication. This review will focus on the innate immune responses against chlamydial infection, highlighting the underlying molecular mechanisms used by the Chlamydia spp. to counteract host innate immune defenses. Insights into these subtle pathogenic mechanisms not only provide a rationale for the augmentation of immune responses against chlamydial infection but also open avenues for further investigation of the molecular mechanisms driving the survival of these clinically important pathogens in host innate immunity.