Low-dose doxycycline induces Chlamydia trachomatis persistence in HeLa cells

Chlamydia trachomatis infection induces ferroptosis and enhances chlamydial replication

Chlamydia trachomatis (C. trachomatis) has been shown to activate multiple programmed cell death pathways, which contribute significantly to host immune responses. Nevertheless, the precise molecular mechanisms by which C. trachomatis induces cell death remain poorly characterized. Ferroptosis, a recently identified form of iron-dependent, lipid peroxidation-driven regulated cell death, may represent a previously unrecognized pathway in chlamydial pathogenesis. To investigate the mechanisms underlying C. trachomatis-induced cell death, we first performed transcriptomic analysis to identify differentially expressed genes and enriched pathways in infected HeLa cells. Concurrently, we quantified intracellular iron levels, reactive oxygen species (ROS) accumulation, and lipid peroxidation, all of which are hallmarks of ferroptosis. Transmission electron microscopy (TEM) further revealed distinct mitochondrial alterations in C. trachomatis-infected cells, suggesting potential dysfunction in cellular redox homeostasis. To directly assess the role of ferroptosis in chlamydial infection, we treated cells with the ferroptosis-specific inhibitor Ferrostatin-1 (Fer-1) and evaluated its effects on chlamydial replication and host inflammatory responses. Bioinformatic analysis demonstrated significant enrichment of iron homeostasis and ferroptosis-related pathways in C. trachomatis-infected cells, with the ferroptosis signaling pathway exhibiting particularly strong activation. Experimentally, infection disrupted the expression of key iron transporters (e.g., TFR and FPN1), causing dysregulated iron uptake and storage. Concurrently, C. trachomatis downregulated the critical ferroptosis inhibitors SLC7A11 and GPX4, leading to elevated lipid peroxidation. Ultrastructural analysis via TEM revealed pronounced mitochondrial abnormalities in infected HeLa cells, including marked swelling and cristae disintegration-a hallmark of ferroptotic damage. Notably, pharmacological inhibition of ferroptosis using Fer-1 not only attenuated infection-induced cell death but also significantly suppressed bacterial replication, suggesting ferroptosis as a host-pathogen interaction nexus. This study provides evidence that C. trachomatis infection induces ferroptosis in host cells, and that targeting the ferroptosis pathway may represent a novel therapeutic strategy for controlling C. trachomatis infections.

A multi-strategy antimicrobial discovery approach reveals new ways to treat Chlamydia

While the excessive use of broad-spectrum antibiotics is a major driver of the global antibiotic resistance crisis, more selective therapies remain unavailable for the majority of bacterial pathogens. This includes the obligate intracellular bacterial pathogens of the genus Chlamydia, which cause millions of urogenital, ocular, and respiratory infections each year. Conducting a comprehensive search of the chemical space for novel antichlamydial activities, we identified over 60 compounds that are chemically diverse, structurally distinct from known antibiotics, non-toxic to human cells, and highly potent in preventing the growth of Chlamydia trachomatis in cell cultures. Some blocked C. trachomatis development reversibly, while others eradicated both established and persistent infections in a bactericidal manner. The top molecules displayed compelling selectivity, yet broad activity against diverse Chlamydia strains and species, including both urogenital and ocular serovars of C. trachomatis, as well as Chlamydia muridarum and Chlamydia caviae. Some compounds also displayed synergies with clinically used antibiotics. Critically, we found the most potent antichlamydial compound to inhibit fatty acid biosynthesis via covalent binding to the active site of Chlamydia FabH, identifying a new mechanism of FabH inhibition and highlighting a possible way to selectively treat Chlamydia infections.

Antimicrobial Resistance in Curable Sexually Transmitted Infections

PURPOSE OF REVIEW

Antimicrobial resistance in sexually transmitted infections (STIs) has become an urgent global public health threat, raising the specter of untreatable infections. This review summarizes the determinants of resistance among the five most common curable STIs Neisseria gonorrhoeae, Chlamydia trachomatis, Mycoplasma genitalium, Treponema pallidum, and Trichomonas vaginalis, as well as strategies to mitigate the spread of resistance.

RECENT FINDINGS

Genetic mutations are key drivers of resistance for N. gonorrhoeae and M. genitalium. Resistance in T. vaginalis can also occur because of genetic mutations, yet differential regulation of genes critical in antibiotic metabolism as well as co-infection with organisms that inactivate therapy play important roles. While resistance in C. trachomatis and T. pallidum has not been a substantial clinical concern, resistance selection via the continued widespread use of antimicrobials remains possible. While resistance determinants are diverse and differ by pathogen, the strategies required to mitigate the continued emergence of resistance are similar: prevention of infection and treatment diversification. Underpinning those strategies, surveillance remains essential for monitoring and responding to the threat of drug-resistant infections.

Structure-Based Design and Synthesis of Covalent Inhibitors for Deubiquitinase and Acetyltransferase ChlaDUB1 of Chlamydia trachomatis

Upon infection by an intracellular pathogen, host cells activate apoptotic pathways to limit pathogen replication. Consequently, efficient proliferation of the obligate intracellular pathogen Chlamydia trachomatis, a major cause of trachoma and sexually transmitted diseases, depends on the suppression of host cell apoptosis. C. trachomatis secretes deubiquitinase ChlaDUB1 into the host cell, leading among other interactions to the stabilization of antiapoptotic proteins and, thus, suppression of host cell apoptosis. Targeting the bacterial effector protein may, therefore, lead to new therapeutic possibilities. To explore the active site of ChlaDUB1, an iterative cycle of computational docking, synthesis, and enzymatic screening was applied with the aim of lead structure development. Hereby, covalent inhibitors were developed, which show enhanced inhibition with a 22-fold increase in IC50 values compared to previous work. Comprehensive insights into the binding prerequisites to ChlaDUB1 are provided, establishing the foundation for an additional specific antichlamydial therapy by small molecules.

Association of Chlamydia trachomatis burden with the vaginal microbiota, bacterial vaginosis, and metronidazole treatment

Bacterial vaginosis (BV), a dysbiosis of the vaginal microbiota, is a common coinfection with Chlamydia trachomatis (Ct), and BV-associated bacteria (BVAB) and their products have been implicated in aiding Ct evade natural immunity. Here, we determined if a non-optimal vaginal microbiota was associated with a higher genital Ct burden and if metronidazole, a standard treatment for BV, would reduce Ct burden or aid in natural clearance of Ct infection. Cervicovaginal samples were collected from women at enrollment and, if testing positive for Ct infection, at a follow-up visit approximately one week later. Cervical Ct burden was assessed by inclusion forming units (IFU) and Ct genome copy number (GCN), and 16S rRNA gene sequencing was used to determine the composition of the vaginal microbiota. We observed a six-log spectrum of IFU and an eight-log spectrum of GCN in our study participants at their enrollment visit, but BV, as indicated by Amsel's criteria, Nugent scoring, or VALENCIA community state typing, did not predict infectious and total Ct burden, although IFU : GCN increased with Amsel and Nugent scores and in BV-like community state types. Ct burden was, however, associated with the abundance of bacterial species in the vaginal microbiota, negatively with Lactobacillus crispatus and positively with Prevotella bivia. Women diagnosed with BV were treated with metronidazole, and Ct burden was significantly reduced in those who resolved BV with treatment. A subset of women naturally cleared Ct infection in the interim, typified by low Ct burden at enrollment and resolution of BV. Abundance of many BVAB decreased, and Lactobacillus increased, in response to metronidazole treatment, but no changes in abundances of specific vaginal bacteria were unique to women who spontaneously cleared Ct infection.

Persistence of obligate intracellular pathogens: alternative strategies to overcome host-specific stresses

In adapting to the intracellular niche, obligate intracellular bacteria usually undergo a reduction of genome size by eliminating genes not needed for intracellular survival. These losses can include, for example, genes involved in nutrient anabolic pathways or in stress response. Living inside a host cell offers a stable environment where intracellular bacteria can limit their exposure to extracellular effectors of the immune system and modulate or outright inhibit intracellular defense mechanisms. However, highlighting an area of vulnerability, these pathogens are dependent on the host cell for nutrients and are very sensitive to conditions that limit nutrient availability. Persistence is a common response shared by evolutionarily divergent bacteria to survive adverse conditions like nutrient deprivation. Development of persistence usually compromises successful antibiotic therapy of bacterial infections and is associated with chronic infections and long-term sequelae for the patients. During persistence, obligate intracellular pathogens are viable but not growing inside their host cell. They can survive for a long period of time such that, when the inducing stress is removed, reactivation of their growth cycles resumes. Given their reduced coding capacity, intracellular bacteria have adapted different response mechanisms. This review gives an overview of the strategies used by the obligate intracellular bacteria, where known, which, unlike model organisms such as E. coli, often lack toxin-antitoxin systems and the stringent response that have been linked to a persister phenotype and amino acid starvation states, respectively.

Characterization and comparison of differentially expressed genes involved in Chlamydia psittaci persistent infection in vitro and in vivo

Chlamydia psittaci is an obligate intracellular zoonotic pathogen that can enter a persistence state in host cells. While the exact pathogenesis is not well understood, this persistence state may play an important role in chronic Chlamydia disease. Here, we assess the effects of chlamydial persistence state in vitro and in vivo by transmission electron microscopy (TEM) and cDNA microarray assays. First, IFN-γ-induced C. psittaci persistence in HeLa cells resulted in the upregulation of 68 genes. These genes are involved in protein translation, carbohydrate metabolism, nucleotide metabolism, lipid metabolism and general stress. However, 109 genes were downregulated following persistent C. psittaci infection, many of which are involved in the TCA cycle, expression regulation and transcription, protein secretion, proteolysis and transport, membrane protein, presumed virulence factor, cell division and late expression. To further study differential gene expression of C. psittaci persistence in vivo, we established an experimentally tractable mouse model of C. psittaci persistence. The C. psittaci-infected mice were gavaged with either water or amoxicillin (amox), and the results indicated that the 20 mg/kg amox-exposed C. psittaci were viable but not infectious. Differentially expressed genes (DEGs) screened by cDNA microarray were detected, and interestingly, the results showed upregulation of three genes (euo, ahpC, prmC) and downregulation of five genes (pbp3, sucB_1, oppA_4, pmpH, ligA) in 20 mg/kg amox-exposed C. psittaci, which suggests that antibiotic treatment in vivo can induce chlamydial persistence state and lead to differential gene expression. However, the discrepancy on inducers between the two models requires more research to supplement. The results may help researchers better understand survival advantages during persistent infection and mechanisms influencing C. psittaci pathogenesis or evasion of the adaptive immune response.