The Chlamydia muridarum plasmid revisited : new insights into growth kinetics

Pgp3 monoclonal antibody inhibits the pathogenicity of Chlamydia muridarum to the genital tract of mice

BACKGROUND

Chlamydia trachomatis (Ct) is the leading cause of tubal inflammation in women, with a high tendency for persistent asymptomatic infections. Antibiotics are currently the primary treatment for Ct infections of the reproductive tract. However, mounting evidence indicates an increasing incidence of persistent infections and recurrence due to antibiotic treatment failure, highlighting the urgent need for novel therapeutic approaches.

METHODS

In this study, a monoclonal antibody against plasmid-encoded protein Pgp3 was prepared using hybridoma technology and its effects on the pathogenicity of Ct were investigated both in vitro and in vivo.

RESULTS

Infectivity of Chlamydia muridarum (Cm) elementary bodies (EBs) increased after incubation with His-Pgp3. When Pgp3mAb-pretreated Ct EBs or Cm-infected cell lysates were used to inoculate HeLa cells, a significantly reduced number of inclusions was observed compared with untreated controls. Cm-infected HeLa cells began to secrete Pgp3 after 6 h. Infection with Cm progeny was significantly inhibited by the addition of Pgp3mAb co-cultured during the first developmental cycle of Cm. Immunofluorescence assays revealed that Pgp3mAb could not enter the host cells. His-Pgp3 stimulated the secretion of IL-6 and IL-8 in human fallopian tube epithelial cells, while Pgp3mAb inhibited this pro-inflammatory effect of His-Pgp3. Cm-infected mice subcutaneously injected with Pgp3mAb demonstrated reduced shedding of live organisms in the lower genital tract, shorter infection cycles, reduced hydrosalpinx, and a reduced inflammatory response.

CONCLUSION

Pgp3 enhanced Cm infectivity in host cells. In vitro, Pgp3mAb inhibited Cm infection by binding to secreted Pgp3 and membrane-bound Pgp3, with a more pronounced effect on secreted Pgp3. Furthermore, Pgp3mAb inhibited the pro-inflammatory effects of Pgp3, thereby attenuating the inflammatory response. Subcutaneous administration of Pgp3mAb effectively reduced Cm-induced pathogenicity in the murine reproductive tract.

Pathobiont-triggered induction of epithelial IDO1 drives regional susceptibility to Inflammatory Bowel Disease

The structure and function of the mammalian gut vary by region, yet why inflammatory diseases manifest in specific regions and not others remains unclear. We use a TNF-overexpressing Crohn's disease (CD) model (TnfΔARE/+), which typically presents in the terminal ileum (TI), to investigate how environmental factors interact with the host's immune susceptibility to drive region-specific disease. We identified Chlamydia muridarum, an intracellular bacterium and murine counterpart to the human sexually transmitted C. trachomatis, as necessary and sufficient to trigger disease manifestation in the ascending colon (AC), another common site of human CD. Disease manifestation in the AC depends on indoleamine 2,3-dioxygenase (IDO1) activity induced by hypersensitive surface secretory cells in genetically susceptible hosts. Single-cell and microbial analyses of human specimens also implicates this pathobiont-epithelial IDO1 pathway in patients with a history of CD in the AC. Our findings demonstrate that genetic and microbial factors can independently drive region-specific disease and provide a unique model to study CD specific to the AC.

Zoonotic and other veterinary chlamydiae - an update, the role of the plasmid and plasmid-mediated transformation

The obligate intracellular bacterial genus Chlamydia harbours species with zoonotic potential, particularly C. psittaci, causative agent of psittacosis, and C. abortus, which may lead to miscarriage in pregnant women. The impact of other bird chlamydiae such as C. avium, C. gallinaceae, and C. buteonis, or reptilian species such as C. crocodili, amongst others, on human health is unclear. The chlamydial native plasmid, a suspected virulence factor, is present in all currently described 14 Chlamydia species except for some plasmid-free strains. The plasmid is also the primary tool to study chlamydial genetics, a still developing field that has mostly focused on C. trachomatis. Only recently, genetic transformation of C. felis, C. pecorum, C. pneumoniae, C. psittaci, and C. suis has succeeded, but existing methods have yet to be refined. In this review article, we will provide an update on the recent developments concerning the zoonotic potential of chlamydiae. Furthermore, we present an overview about the current state of knowledge regarding the chlamydial plasmid in terms of prevalence and significance as a virulence factor. Finally, we give insights into the progress of developing genetic tools for chlamydial species other than C. trachomatis with a special focus on zoonotic and veterinary chlamydiae.

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.

Interferon-ε as potential inhibitor of Chlamydia trachomatis infection

Chlamydia trachomatis, the main cause of bacterial sexually transmitted diseases, is responsible for severe reproductive sequelae. Amongst all the cytokines involved in host immunity towards this pathogen, IFN-ε has recently acquired importance for its potential contribution to the female reproductive tract innate defenses. Herein, our study aimed to explore, for the first time, the activity of IFN-ε toward C. trachomatis in an in vitro infection model, by testing its effects on the different phases of chlamydial developmental cycle, as well as on the ultrastructural characteristics of chlamydial inclusions, via transmission electron microscopy. Main result is the capability of IFN-ε to alter C. trachomatis growth, as suggested by reduced infectious progenies, as well as a patchy distribution of bacteria and altered morphology of reticulate bodies within inclusions. In conclusion, our results suggest that IFN-ε could play a role in the innate and adaptive immune defenses against C. trachomatis; in the future, it will be needed to investigate its activity on an infection model more closely resembling the physiological environment of the female genital tract.

Plasmid-mediated virulence in Chlamydia

Chlamydia trachomatis infection of ocular conjunctiva can lead to blindness, while infection of the female genital tract can lead to chronic pelvic pain, ectopic pregnancy, and/or infertility. Conjunctival and fallopian tube inflammation and the resulting disease sequelae are attributed to immune responses induced by chlamydial infection at these mucosal sites. The conserved chlamydial plasmid has been implicated in enhancing infection, via improved host cell entry and exit, and accelerating innate inflammatory responses that lead to tissue damage. The chlamydial plasmid encodes eight open reading frames, three of which have been associated with virulence: a secreted protein, Pgp3, and putative transcriptional regulators, Pgp4 and Pgp5. Although Pgp3 is an important plasmid-encoded virulence factor, recent studies suggest that chlamydial plasmid-mediated virulence extends beyond the expression of Pgp3. In this review, we discuss studies of genital, ocular, and gastrointestinal infection with C. trachomatis or C. muridarum that shed light on the role of the plasmid in disease development, and the potential for tissue and species-specific differences in plasmid-mediated pathogenesis. We also review evidence that plasmid-associated inflammation can be independent of bacterial burden. The functions of each of the plasmid-encoded proteins and potential molecular mechanisms for their role(s) in chlamydial virulence are discussed. Although the understanding of plasmid-associated virulence has expanded within the last decade, many questions related to how and to what extent the plasmid influences chlamydial infectivity and inflammation remain unknown, particularly with respect to human infections. Elucidating the answers to these questions could improve our understanding of how chlamydia augment infection and inflammation to cause disease.

Extra Virgin Olive Oil-Based Formulations: A "Green" Strategy against Chlamydia trachomatis

In recent decades, antibiotic misuse has emerged as an important risk factor for the appearance of multi-drug-resistant bacteria, and, recently, antimicrobial resistance has also been described in Chlamydia trachomatis as the leading cause of bacterial sexually transmitted diseases worldwide. Herein, we investigated, for the first time, the antibacterial activity against C. trachomatis of a polyphenolic extract of extra virgin olive oil (EVOO), alongside purified oleocanthal and oleacein, two of its main components, in natural deep eutectic solvent (NaDES), a biocompatible solvent. The anti-chlamydial activity of olive-oil polyphenols (OOPs) was tested in the different phases of chlamydial developmental cycle by using an in vitro infection model. Transmission and scanning electron microscopy analysis were performed for investigating potential alterations of adhesion and invasion, as well as morphology, of chlamydial elementary bodies (EBs) to host cells. The main result of our study is the anti-bacterial activity of OOPs towards C. trachomatis EBs down to a total polyphenol concentration of 1.7 μg/mL, as shown by a statistically significant decrease (93.53%) of the total number of chlamydial-inclusion-forming units (p < 0.0001). Transmission and scanning electron microscopy analysis supported its anti-chlamydial effect, suggesting that OOP might damage the chlamydial outer layers, impairing their structural integrity and hindering EB capability to infect the host cell. In conclusion, OOPs may represent an interesting alternative therapeutic option toward C. trachomatis, although further studies are necessary for exploring its clinical applications.

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.

Transformation and Mutagenesis of Chlamydia trachomatis and C. muridarum Utilizing pKW Vector

A gene deletion by allelic exchange via homologous recombination from a bacterial genome represents a valuable genetic tool for studying a role(s) of determinants involved in various aspects of pathogenesis. Due to chlamydial obligate intracellular lifestyle and comparatively low transformation rate, the mutagenesis of Chlamydia utilizes types of suicide vectors that have to be maintained and propagated by the bacteria throughout several rounds of their intracellular developmental cycle. These deletion constructs must be lost by chlamydiae once null mutant formation is achieved. pKW is a small, 5.45 bp, pUC19-derived vector, which has been recently successfully employed for the generation of deletion mutants in C. trachomatis, serovariant D, and C. muridarum. This vector contains both, E. coli as well as chlamydial species-specific plasmid origins of replication, allowing for its propagation by both bacterial genera under a selective pressure. However, once the selective antibiotic is removed from culture, chlamydiae rapidly lose pKW, and the subsequent reintroduction of the selective antibiotic back to chlamydiae-infected cells results efficiently in the selection of generated deletion mutants. Protocols provided here describe in detail the preparation of pKW deletion constructs for C. trachomatis and C. muridarum applicable for chlamydial transformation and the production of null mutant in non-essential genes. Protocols provided here, are describing in detail methods for assembly of the pKW shuttle vector and generation of deletion mutants in C. trachomatis and C. muridarum. © 2023 Wiley Periodicals LLC. Basic Protocol 1: Assembly of pKW shuttle vector Basic Protocol 2: Generation of a deletion mutant in C. trachomatis, serovars D and L2 and, Chlamydia muridarum Support Protocol: Transformation of C. trachomatis, serovars B.

Virulence Protein Pgp3 Is Insufficient To Mediate Plasmid-Dependent Infectivity of Chlamydia trachomatis

Chlamydia trachomatis is the most common cause of infectious blindness and sexually transmitted bacterial infection globally. C. trachomatis contains a conserved chlamydial plasmid with eight coding sequences. Plasmid-cured Chlamydia strains are attenuated and display reduced infectivity in cell culture and in vivo genital infection of female mice. Mutants that do not express the plasmid-encoded proteins Pgp3, a secreted protein with unknown function, or Pgp4, a putative regulator of pgp3 and other chromosomal loci, display an infectivity defect similar to plasmid-deficient strains. Our objective was to determine the combined and individual contributions of Pgp3 and Pgp4 to this phenotype. Deletion of pgp3 and pgp4 resulted in an infectivity defect detected by competition assay in cell culture and in mice. The pgp3 locus was placed under the control of an anhydrotetracycline-inducible promoter to examine the individual contributions of Pgp3 and Pgp4 to infectivity. Expression of pgp3 was induced 100- to 1,000-fold after anhydrotetracycline administration, regardless of the presence or absence of pgp4. However, secreted Pgp3 was not detected when pgp4 was deleted, confirming a role for Pgp4 in Pgp3 secretion. We discovered that expression of pgp3 or pgp4 alone was insufficient to restore normal infectivity, which required expression of both Pgp3 and Pgp4. These results suggest Pgp3 and Pgp4 are both required for infectivity during C. trachomatis infection. Future studies are required to determine the mechanism by which Pgp3 and Pgp4 influence chlamydial infectivity as well as the potential roles of Pgp4-regulated loci.

Differential Effects of Small Molecule Inhibitors on the Intracellular Chlamydia Infection

Chlamydia are obligate intracellular bacteria that reside within a membrane-bound compartment called the chlamydial inclusion inside a eukaryotic host cell. These pathogens have a complex biphasic developmental cycle, which involves conversion between a replicating, but noninfectious, reticulate body (RB) and an infectious elementary body (EB). Small molecule inhibitors have been reported to have deleterious effects on the intracellular Chlamydia infection, but these studies have typically been limited in terms of assays and time points of analysis. We compared published and novel inhibitors and showed that they can differentially alter inclusion size, chlamydial number and infectious EB production, and that these effects can vary over the course of the intracellular infection. Our results provide the justification for analysis with multiple assays performed either at the end of the infection or over a time course. We also show that this approach has the potential to identify the particular step in the developmental cycle that is impacted by the inhibitor. We furthermore propose that the magnitude of inhibitor-induced progeny defects are best quantified and compared by using a new value called maximal progeny production (Progeny_max). As a demonstration of the validity of this systematic approach, we applied it to inhibitors of Akt and AMPK, which are host kinases involved in lipid synthesis and cholesterol trafficking pathways. Both inhibitors reduced EB production, but Akt disruption primarily decreased RB-to-EB conversion while AMPK inhibition paradoxically enhanced RB replication.

In Vitro Modelling of Chlamydia trachomatis Infection in the Etiopathogenesis of Male Infertility and Reactive Arthritis

Chlamydia trachomatis is an obligate, intracellular bacterium responsible for a range of diseases of public health importance, since C. trachomatis infection is often asymptomatic and, hence, untreated, leading to chronic complications, including prostatitis, infertility, and reactive arthritis. The ample spectrum of diseases caused by C. trachomatis infection is reflected in its ability to infect and multiply within a wide range of different cell types. Cervical epithelial cells, to date, have been the most studied cellular infection model, highlighting the peculiar features of the host-cell inflammatory and immune responses to the infection. Herein, we provide the up-to-date evidence on the interaction between C. trachomatis and human prostate epithelial, Sertoli and synovial cells.

In-cell western assay as a high-throughput approach for Chlamydia trachomatis quantification and susceptibility testing to antimicrobials

Chlamydia trachomatis, the leading cause of bacterial sexually transmitted diseases in developed countries, with around 127 million new cases per year, is mainly responsible for urethritis and cervicitis in women, and urethritis and epididymitis in men. Most C. trachomatis infections remain asymptomatic (>50%) and, hence, untreated, leading to severe reproductive complications in both women and men, like infertility. Therefore, the detection of C. trachomatis as well as the antimicrobial susceptibility testing becomes a priority, and, along the years, several methods have been recommended, like cell culture and direct immunofluorescence (DFA) on cell cultures. Herein, we described the application of In-Cell Western assay (ICW) via Odyssey CLx as a fast, more accessible, and high-throughput platform for the quantification of C. trachomatis and the screening of anti-chlamydial drugs. As a first step, we set up a standard curve by infecting cell monolayers with 2-fold serial dilutions of C. trachomatis Elementary Body (EB) suspension. Then, different unknown C. trachomatis EB suspensions were quantified and the chlamydial susceptibility testing to erythromycin was performed, using the DFA as comparison. Our results showed a very high concordance between these two assays, as evidenced by the enumeration of chlamydial IFUs as well as the determination of erythromycin Minimum Inhibitory Concentration (MIC). In conclusion, the ICW assay may be a promising candidate as an accurate and accessible methodology for C. trachomatis antimicrobial susceptibility testing.

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 muridarum Can Invade the Central Nervous System via the Olfactory and Trigeminal Nerves and Infect Peripheral Nerve Glial Cells

Chlamydia pneumoniae can infect the brain and has been linked to late-onset dementia. Chlamydia muridarum, which infects mice, is often used to model human chlamydial infections. While it has been suggested to be also important for modelling brain infection, nervous system infection by C. muridarum has not been reported in the literature. C. pneumoniae has been shown to infect the olfactory bulb in mice after intranasal inoculation, and has therefore been suggested to invade the brain via the olfactory nerve; however, nerve infection has not been shown to date. Another path by which certain bacteria can reach the brain is via the trigeminal nerve, but it remains unknown whether Chlamydia species can infect this nerve. Other bacteria that can invade the brain via the olfactory and/or trigeminal nerve can do so rapidly, however, whether Chlamydia spp. can reach the brain earlier than one-week post inoculation remains unknown. In the current study, we showed that C. muridarum can within 48 h invade the brain via the olfactory nerve, in addition to infecting the trigeminal nerve. We also cultured the glial cells of the olfactory and trigeminal nerves and showed that C. muridarum readily infected the cells, constituting a possible cellular mechanism explaining how the bacteria can invade the nerves without being eliminated by glial immune functions. Further, we demonstrated that olfactory and trigeminal glia differed in their responses to C. muridarum, with olfactory glia showing less infection and stronger immune response than trigeminal glia.

Chlamydia trachomatis and Chlamydia muridarum spectinomycin resistant vectors and a transcriptional fluorescent reporter to monitor conversion from replicative to infectious bacteria

Chlamydia trachomatis infections are the leading cause of sexually transmitted infections of bacterial origin. Lower genital tract infections are often asymptomatic, and therefore left untreated, leading to ascending infections that have long-term consequences on female reproductive health. Human pathology can be recapitulated in mice with the mouse adapted strain C. muridarum. Eight years into the post-genetic era, significant advances to expand the Chlamydia genetic toolbox have been made to facilitate the study of this important human pathogen. However, the need for additional tools remains, especially for C. muridarum. Here, we describe a new set of spectinomycin resistant E. coli-Chlamydia shuttle vectors, for C. trachomatis and C. muridarum. These versatile vectors allow for expression and localization studies of Chlamydia effectors, such as Inc proteins, and will be instrumental for mutant complementation studies. In addition, we have exploited the differential expression of specific Chlamydia genes during the developmental cycle to engineer an omcA::gfp fluorescent transcriptional reporter. This novel tool allows for monitoring RB to EB conversion at the bacterial level. Spatiotemporal tracking of GFP expression within individual inclusions revealed that RB to EB conversion initiates in bacteria located at the edge of the inclusion and correlates with the time post initiation of bacterial replication and inclusion size. Comparison between primary and secondary inclusions potentially suggests that the environment in which the inclusions develop influences the timing of conversion. Altogether, the Chlamydia genetic tools described here will benefit the field, as we continue to investigate the molecular mechanisms underlying Chlamydia-host interaction and pathogenesis.

Growth kinetics of Chlamydia trachomatis in primary human Sertoli cells

Chlamydia trachomatis (Ct) is the leading cause of bacterial sexually transmitted infections worldwide and has been associated with male infertility. Recently, it was hypothesized that Ct may infect the epithelium of the seminiferous tubule, formed by Sertoli cells, thus leading to impaired spermatogenesis. To date, there is a lack of data on Ct infection of the seminiferous epithelium; therefore, we aimed to characterize, for the first time, an in vitro infection model of primary human Sertoli cells. We compared Ct inclusion size, morphology and growth kinetics with those in McCoy cells and we studied F-actin fibres, Vimentin-based intermediate filaments and α-tubulin microtubules in Sertoli and McCoy cells. Our main finding highlighted the ability of Ct to infect Sertoli cells, although with a unique growth profile and the inability to exit host cells. Furthermore, we observed alterations in the cytoskeletal fibres of infected Sertoli cells. Our results suggest that Ct struggles to generate a productive infection in Sertoli cells, limiting its dissemination in the host. Nevertheless, the adverse effect on the cytoskeleton supports the notion that Ct may compromise the blood-testis barrier, impairing spermatogenesis.

In vitro analysis of genetically distinct Chlamydia pecorum isolates reveals key growth differences in mammalian epithelial and immune cells

Chlamydia (C.) pecorum is an obligate intracellular bacterium that infects and causes disease in a broad range of animal hosts. Molecular studies have revealed that this pathogen is genetically diverse with certain isolates linked to different disease outcomes. Limited in vitro or in vivo data exist to support these observations, further hampering efforts to improve our understanding of C. pecorum pathogenesis. In this study, we evaluated whether genetically distinct C. pecorum isolates (IPA, E58, 1710S, W73, JP-1-751) display different in vitro growth phenotypes in different mammalian epithelial and immune cells. In McCoy cells, shorter lag phases were observed for W73 and JP-1-751 isolates. Significantly smaller inclusions were observed for the naturally plasmid-free E58 isolate. C. pecorum isolates of bovine (E58) and ovine origin (IPA, W73, JP-1-751) grew faster in bovine cells compared to a porcine isolate (1710S). C. pecorum isolates could infect but appear not able to complete their developmental cycle in bovine peripheral neutrophil granulocytes. All isolates, except 1710S, could multiply in bovine monocyte-derived macrophages. These results reveal potentially important phenotypic differences that will help to understand the pathogenesis of C. pecorum in vivo and to identify C. pecorum virulence factors.