Chlamydia Outer Protein (Cop) B from Chlamydia pneumoniae possesses characteristic features of a type III secretion (T3S) translocator protein

From coughs to complications: the story of Chlamydia pneumoniae

Chlamydia pneumoniae is an obligate intracellular bacterium and a significant cause of respiratory infections. It is associated with upper and lower respiratory tract diseases, including bronchitis and pneumonia. The pathogen employs specific virulence factors, such as the Type III Secretion System (T3SS) and Inc proteins, to invade and subvert host cell machinery during its peculiar developmental life cycle. Chronic infections have been linked to asthma and, more controversially, to atherosclerosis and neurodegenerative diseases. Diagnosis primarily relies on PCR-based molecular assays, while treatment includes macrolides, tetracyclines or fluoroquinolones. Despite its clinical relevance, research on C. pneumoniae has declined in recent years, highlighting the need for renewed scientific focus.

CT584 Is Not a Protective Vaccine Antigen against Respiratory Chlamydial Challenge in Mice

Background:Chlamydia trachomatis is the most prevalent bacterial sexually transmitted pathogen in humans worldwide. Since chlamydial infection is largely asymptomatic with the potential for serious complications, a preventative vaccine is likely the most viable long-term answer to this public health threat. Cell-free protein synthesis (CFPS) utilizes the cellular protein manufacturing machinery decoupled from the requirement for maintaining cellular viability, offering the potential for flexible, rapid, and decentralized production of recombinant protein vaccine antigens. Methods: Here, we use CFPS to produce the full-length putative chlamydial type three secretion system (T3SS) needle-tip protein, CT584, for evaluation as a vaccine antigen in mouse models. High-speed atomic force microscopy (HS-AFM) (RIBM, Tsukuba, Japan) imaging and computer simulations confirm that CFPS-produced CT584 retains a native-like structure prior to immunization. Female mice were primed with CT584 adjuvanted with CpG-1826 intranasally (i.n.) or CpG-1826 + Montanide ISA 720 intramuscularly (i.m.), followed four weeks later by an i.m. boost before respiratory challenge with 104 inclusion forming units (IFU) of Chlamydia muridarum. Results: Immunization with CT584 generated robust antibody responses but weak cell-mediated immunity and failed to protect against i.n. challenge as demonstrated by body weight loss, increased lung weights, and the presence of high numbers of IFUs in the lungs. Conclusion: While CT584 was not a protective vaccine candidate, the speed and flexibility with which CFPS can be used to produce other potential chlamydial antigens make it an attractive technique for antigen production.

Lactoferrin impairs pathogen virulence through its proteolytic activity

Antibiotics, often hailed as 'miracle drugs' in the 20th century, have revolutionised medicine by saving millions of lives in human and veterinary medicine, effectively combatting bacterial infections. However, the escalating global challenge of antimicrobial resistance and the appearance and spread of multidrug-resistant pathogens necessitates research into alternatives. One such alternative could be lactoferrin. Lactoferrin, an iron-binding multifunctional protein, is abundantly present in mammalian secretions and exhibits antimicrobial and immunomodulatory activities. An often overlooked aspect of lactoferrin is its proteolytic activity, which could contribute to its antibacterial activity. The proteolytic activity of lactoferrin has been linked to the degradation of virulence factors from several bacterial pathogens, impeding their colonisation and potentially limiting their pathogenicity. Despite numerous studies, the exact proteolytically active site of lactoferrin, the specific bacterial virulence factors it degrades and the underlying mechanism remain incompletely understood. This review gives an overview of the current knowledge concerning the proteolytic activity of lactoferrins and summarises the bacterial virulence factors degraded by lactoferrins. We further detail how a deeper understanding of the proteolytic activity of lactoferrin might position it as a viable alternative for antibiotics, being crucial to halt the spread of multi-drug resistant bacteria.

Evaluation in mice of cell-free produced CT584 as a Chlamydia vaccine antigen

Chlamydia trachomatis is the most prevalent bacterial sexually transmitted pathogen worldwide. Since chlamydial infection is largely asymptomatic with the potential for serious complications, a preventative vaccine is likely the most viable long-term answer to this public health threat. Cell-free protein synthesis (CFPS) utilizes the cellular protein manufacturing machinery decoupled from the requirement for maintaining cellular viability, offering the potential for flexible, rapid, and de-centralized production of recombinant protein vaccine antigens. Here, we use CFPS to produce the putative chlamydial type three secretion system (T3SS) needle-tip protein, CT584, for use as a vaccine antigen in mouse models. High-speed atomic force microscopy (HS-AFM) imaging and computer simulations confirm that CFPS-produced CT584 retains a native-like structure prior to immunization. Female mice were primed with CT584 adjuvanted with CpG-1826 intranasally (i.n.) or CpG-1826 + Montanide ISA 720 intramuscularly (i.m.), followed four-weeks later by an i.m. boost before respiratory challenge with 104 inclusion forming units (IFU) of Chlamydia muridarum. Immunization with CT584 generated robust antibody responses but weak cell mediated immunity and failed to protect against i.n. challenge as demonstrated by body weight loss, increased lungs' weights and the presence of high numbers of IFUs in the lungs. While CT584 alone may not be the ideal vaccine candidate, the speed and flexibility with which CFPS can be used to produce other potential chlamydial antigens makes it an attractive technique for antigen production.

Euo is a developmental regulator that represses late genes and activates midcycle genes in Chlamydia trachomatis

IMPORTANCE

In this study, we developed a correlative approach that combined DNA immunoprecipitation-seq and RNA-seq analyses to define the regulon of the Chlamydia trachomatis transcription factor Euo. We confirmed the proposed role of Euo as a transcriptional repressor of late chlamydial genes but also showed that Euo activates transcription of a subset of midcycle genes and autoregulates its own expression via negative feedback. This study validates and expands the role of Euo as an important developmental regulator in C. trachomatis. In addition, this genome-wide correlative approach can be applied to study transcription factors in other pathogenic bacteria.

Type III Secretion in Chlamydia

Type III secretion systems (T3SSs) are utilized by Gram-negative pathogens to enhance their pathogenesis. This secretion system is associated with the delivery of effectors through a needle-like structure from the bacterial cytosol directly into a target eukaryotic cell. These effector proteins then manipulate specific eukaryotic cell functions to benefit pathogen survival within the host. The obligate intracellular pathogens of the family Chlamydiaceae have a highly evolutionarily conserved nonflagellar T3SS that is an absolute requirement for their survival and propagation within the host with about one-seventh of the genome dedicated to genes associated with the T3SS apparatus, chaperones, and effectors. Chlamydiae also have a unique biphasic developmental cycle where the organism alternates between an infectious elementary body (EB) and replicative reticulate body (RB). T3SS structures have been visualized on both EBs and RBs. And there are effector proteins that function at each stage of the chlamydial developmental cycle, including entry and egress. This review will discuss the history of the discovery of chlamydial T3SS and the biochemical characterization of components of the T3SS apparatus and associated chaperones in the absence of chlamydial genetic tools. These data will be contextualized into how the T3SS apparatus functions throughout the chlamydial developmental cycle and the utility of heterologous/surrogate models to study chlamydial T3SS. Finally, there will be a targeted discussion on the history of chlamydial effectors and recent advances in the field.

Chlamydia: what is on the outside does matter

This review summarises major highlights on the structural biology of the chlamydial envelope. Chlamydiae are obligate intracellular bacteria, characterised by a unique biphasic developmental cycle. Depending on the stage of their lifecycle, they appear in the form of elementary or reticulate bodies. Since these particles have distinctive functions, it is not surprising that their envelope differs in lipid as well as in protein content. Vice versa, by identifying surface proteins, specific characteristics of the particles such as rigidity or immunogenicity may be deduced. Detailed information on the bacterial membranes will increase our understanding on the host-pathogen interactions chlamydiae employ to survive and grow and might lead to new strategies to battle chlamydial infections.

iTRAQ-Based Quantitative Proteomics Analysis of HeLa Cells Infected With Chlamydia muridarum TC0668 Mutant and Wild-Type Strains

Chlamydia muridarum, an obligate intracellular pathogen, was used to establish a murine model of female upper genital tract infection by Chlamydia trachomatis. TC0668 in C. muridarum is a hypothetical chromosomal virulence protein that is involved in upper genital tract pathogenesis. The infection of mice with the C. muridarum TC0668-mutant (G216*) strain results in less pathological damage in the upper genital tract. In this study, an isobaric tags for relative and absolute quantitation (iTRAQ)-based quantitative proteomics analysis was performed to identify differentially expressed proteins between TC0668 wild-type (TC0668^wt) and TC0668 mutant (TC0668^mut) strains at 6, 12, 18, and 24 h post-infection (p.i.). Of the 550 proteins differentially expressed at 18 h p.i., 222 and 328 were up-regulated and down-regulated, respectively, inTC0668^mut-infected cells. The expression of seven up-regulated proteins (encoded by SRPRB, JAK1, PMM1, HLA-DQB1, THBS1, ITPR1, and BCAP31) and three down-regulated proteins (encoded by MAPKAPK2, TRAFD1, and IFI16) from the iTRAQ analysis were validated using quantitative real-time (qRT)-PCR. The qRT-PCR results were consistent with those of iTRAQ. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses revealed that the differentially expressed proteins primarily participated in inflammatory responses, fibrosis, metabolic processes, and complement coagulation cascades, and were mainly enriched in the phosphatidylinositol 3′-kinase (PI3K)/Akt, nuclear factor kappa-B (NF-κB), and other signaling pathways. Using western-blotting and immunofluorescence detection, significant differences in activation of the PI3K/Akt and NF-κB signaling pathways were observed between the TC0668^wt- and TC0668^mut-infected cells. Differentially expressed proteins linked with inflammation and fibrosis were used in a protein-protein interaction network analysis. The results suggest that TC0668 may play a pivotal role in C. muridarum-induced genital pathology by inducing inflammatory responses and fibrosis, which may involve the activation of the PI3K/Akt and NF-κB signaling pathways.

Chlamydial Infection From Outside to Inside

Chlamydia are obligate intracellular bacteria, characterized by a unique biphasic developmental cycle. Specific interactions with the host cell are crucial for the bacteria’s survival and amplification because of the reduced chlamydial genome. At the start of infection, pathogen-host interactions are set in place in order for Chlamydia to enter the host cell and reach the nutrient-rich peri-Golgi region. Once intracellular localization is established, interactions with organelles and pathways of the host cell enable the necessary hijacking of host-derived nutrients. Detailed information on the aforementioned processes will increase our understanding on the intracellular pathogenesis of chlamydiae and hence might lead to new strategies to battle chlamydial infection. This review summarizes how chlamydiae generate their intracellular niche in the host cell, acquire host-derived nutrients in order to enable their growth and finally exit the host cell in order to infect new cells. Moreover, the evolution in the development of molecular genetic tools, necessary for studying the chlamydial infection biology in more depth, is discussed in great detail.

Otopathogenic Pseudomonas aeruginosa Enters and Survives Inside Macrophages

Otitis media (OM) is a broad term describing a group of infectious and inflammatory disorders of the middle ear. Despite antibiotic therapy, acute OM can progress to chronic suppurative otitis media (CSOM) characterized by ear drum perforation and purulent discharge. Pseudomonas aeruginosa is the most common pathogen associated with CSOM. Although, macrophages play an important role in innate immune responses but their role in the pathogenesis of P. aeruginosa-induced CSOM is not known. The objective of this study is to examine the interaction of P. aeruginosa with primary macrophages. We observed that P. aeruginosa enters and multiplies inside human and mouse primary macrophages. This bacterial entry in macrophages requires both microtubule and actin dependent processes. Transmission electron microscopy demonstrated that P. aeruginosa was present in membrane bound vesicles inside macrophages. Interestingly, deletion of oprF expression in P. aeruginosa abrogates its ability to survive inside macrophages. Our results suggest that otopathogenic P. aeruginosa entry and survival inside macrophages is OprF-dependent. The survival of bacteria inside macrophages will lead to evasion of killing and this lack of pathogen clearance by phagocytes contributes to the persistence of infection in CSOM. Understanding host-pathogen interaction will provide novel avenues to design effective treatment modalities against OM.

Immunization with chlamydial type III secretion antigens reduces vaginal shedding and prevents fallopian tube pathology following live C. muridarum challenge

Chlamydia trachomatis infections in women are often asymptomatic and if left untreated can lead to significant late sequelae including pelvic inflammatory disease and tubal factor infertility. Vaccine development efforts over the past three decades have been unproductive and there is no vaccine approved for use in humans. The existence of serologically distinct strains or serovars of C. trachomatis mandates a vaccine that will provide protection against multiple serovars. Chlamydia spp. use a highly conserved type III secretion system (T3SS) composed of both structural and effector proteins which is an essential virulence factor for infection and intracellular replication. In this study we evaluated a novel fusion protein antigen (BD584) which consists of three T3SS proteins from C. trachomatis (CopB, CopD, and CT584) as a potential chlamydial vaccine candidate. Intranasal immunization with BD584 elicited serum neutralizing antibodies that inhibited C. trachomatis infection in vitro. Following intravaginal challenge with C. muridarum, immunized mice had a 95% reduction in chlamydial shedding from the vagina at the peak of infection and cleared the infection sooner than control mice. Immunization with BD584 also reduced the rate of hydrosalpinx by 87.5% compared to control mice. Together, these results suggest that highly conserved proteins of the chlamydial T3SS may represent good candidates for a Chlamydia vaccine.

A working model for the type III secretion mechanism in Chlamydia

It has been appreciated for almost 20 years that members of the Chlamydiales possess a virulence-associated type III secretion mechanism. Given the obligate intracellular nature of these bacteria, defining exactly how type III secretion functions to promote pathogenesis has been challenging. We present a working model herein that is based on current evidence.