Impact of a low-oxygen environment on the efficacy of antimicrobials against intracellular Chlamydia trachomatis

Sorangicin A Is Active against Chlamydia in Cell Culture, Explanted Fallopian Tubes, and Topical In Vivo Treatment

Current treatment of Chlamydia trachomatis using doxycycline and azithromycin introduces detrimental side effects on the host's microbiota. As a potential alternative treatment, the myxobacterial natural product sorangicin A (SorA) blocks the bacterial RNA polymerase. In this study we analyzed the effectiveness of SorA against C. trachomatis in cell culture, and explanted fallopian tubes and systemic and local treatment in mice, providing also pharmacokinetic data on SorA. Potential side effects of SorA on the vaginal and gut microbiome were assessed in mice and against human-derived Lactobacillus species. SorA showed minimal inhibitory concentrations of 80 ng/mL (normoxia) to 120 ng/mL (hypoxia) against C. trachomatis in vitro and was eradicating C. trachomatis at a concentration of 1 µg/mL from fallopian tubes. In vivo, SorA reduced chlamydial shedding by more than 100-fold within the first days of infection by topical application corresponding with vaginal detection of SorA only upon topical treatment, but not after systemic application. SorA changed gut microbial composition during intraperitoneal application only and did neither alter the vaginal microbiota in mice nor affect growth of human-derived lactobacilli. Additional dose escalations and/or pharmaceutical modifications will be needed to optimize application of SorA and to reach sufficient anti-chlamydial activity in vivo.

Chlamydia trachomatis L2/434/Bu Favors Hypoxia for its Growth in Human Lymphoid Jurkat Cells While Maintaining Production of Proinflammatory Cytokines

The role of lymphocytes as a cornerstone of the inflammatory response in the invasive pathogenesis of Chlamydia trachomatis (Ct) LGV (L1-3) infection is unclear. Therefore, we assessed whether the adaptation of CtL2 to immortal lymphoid Jurkat cells under hypoxic conditions occurred through proinflammatory cytokine profile modification. The quantities of inclusion-forming units with chlamydial 16S rDNA confirmed that CtL2 grew well under hypoxic rather than normoxic conditions in the cells. Confocal microscopic imaging and transmission electron microscopy revealed the presence of bacterial progeny in the inclusions and showed that the inclusions were larger under hypoxic rather than normoxic conditions; this was supported by the results of 3D image construction. Furthermore, PCR-based analysis of proinflammatory cytokines revealed that the gene expression levels under hypoxic conditions were significantly higher than those under normoxic conditions. In particular, the expression of two genes (CXCL8 and CXCR3) was significantly diminished under normoxic conditions. Taken together, the results indicated that hypoxia promoted CtL2 growth in Jurkat cells while maintaining the levels of proinflammatory cytokines. Thus, Ct LGV infection in lymphocytes under hypoxic conditions might be crucial to a complete understanding of the invasive pathogenesis.

Chlamydia trachomatis Requires Functional Host-Cell Mitochondria and NADPH Oxidase 4/p38MAPK Signaling for Growth in Normoxia

Chlamydia trachomatis (Ct) is an intracellular energy-parasitic bacterium that requires ATP derived from infected cells for its growth. Meanwhile, depending on the O₂ concentration, the host cells change their mode of ATP production between oxidative phosphorylation in mitochondria (Mt) and glycolysis; this change depends on signaling via reactive oxygen species (ROS) produced by NADPH oxidases (NOXs) as well as Mt. It has been proposed that Ct correspondingly switches its source of acquisition of ATP between host-cell Mt and glycolysis, but this has not been verified experimentally. In the present study, we assessed the roles of host-cell NOXs and Mt in the intracellular growth of CtL2 (L2 434/Bu) under normoxia (21% O₂) and hypoxia (2% O₂) by using several inhibitors of NOXs (or the downstream molecule) and Mt-dysfunctional (Mt^d) HEp-2 cells. Under normoxia, diphenyleneiodonium, an inhibitor of ROS diffusion, abolished the growth of CtL2 and other Chlamydiae (CtD and C. pneumoniae). Both ML171 (a pan-NOX inhibitor) and GLX351322 (a NOX4-specific inhibitor) impaired the growth of CtL2 under normoxia, but not hypoxia. NOX4-knockdown cells diminished the bacterial growth. SB203580, an inhibitor of the NOX4-downstream molecule p38MAPK, also inhibited the growth of CtL2 under normoxia but not hypoxia. Furthermore, CtL2 failed to grow in Mt^d cells under normoxia, but no effect was observed under hypoxia. We conclude that under normoxia, Ct requires functional Mt in its host cells as an ATP source, and that this process requires NOX4/p38MAPK signaling in the host cells. In contrast to hypoxia, crosstalk between NOX4 and Mt via p38MAPK may be crucial for the growth of Ct under normoxia.

Impact of First-Line Antimicrobials on Chlamydia trachomatis-Induced Changes in Host Metabolism and Cytokine Production

Urogenital infections with Chlamydia trachomatis (C. trachomatis) are the most common bacterial sexually transmitted diseases worldwide. As an obligate intracellular bacterium, chlamydial replication and pathogenesis depends on the host metabolic activity. First-line antimicrobials such as doxycycline (DOX) and azithromycin (AZM) have been recommended for the treatment of C. trachomatis infection. However, accumulating evidence suggests that treatment with AZM causes higher rates of treatment failure than DOX. Here, we show that an inferior efficacy of AZM compared to DOX is associated with the metabolic status of host cells. Chlamydial metabolism and infectious progeny of C. trachomatis were suppressed by therapeutic relevant serum concentrations of DOX or AZM. However, treatment with AZM could not suppress host cell metabolic pathways, such as glycolysis and mitochondrial oxidative phosphorylation, which are manipulated by C. trachomatis. The host cell metabolic activity was associated with a significant reactivation of C. trachomatis after removal of AZM treatment, but not after DOX treatment. Furthermore, AZM insufficiently attenuated interleukin (IL)-8 expression upon C. trachomatis infection and higher concentrations of AZM above therapeutic serum concentration were required for effective suppression of IL-8. Our data highlight that AZM is not as efficient as DOX to revert host metabolism in C. trachomatis infection. Furthermore, insufficient treatment with AZM failed to inhibit chlamydial reactivation as well as C. trachomatis induced cytokine responses. Its functional relevance and the impact on disease progression have to be further elucidated in vivo.

Hypoxia promotes Chlamydia trachomatis L2/434/Bu growth in immortal human epithelial cells via activation of the PI3K-AKT pathway and maintenance of a balanced NAD+/NADH ratio

Chlamydia trachomatis LGV (CtL2) causes systemic infection and proliferates in lymph nodes as well as genital tract or rectum producing a robust inflammatory response, presumably leading to a low oxygen environment. We therefore assessed how CtL2 growth in immortal human epithelial cells adapts to hypoxic conditions. Assessment of inclusion forming units, the quantity of chlamydial 16S rDNA, and inclusion size showed that hypoxia promotes CtL2 growth. Under hypoxia, HIF-1α was stabilized and p53 was degraded in infected cells. Moreover, AKT was strongly phosphorylated at S473 by CtL2 infection. This activation was significantly diminished by LY-294002, a PI3K-AKT inhibitor, which decreased the number of CtL2 progeny. HIF-1α stabilizers (CoCl₂, desferrioxamine) had no effect on increasing CtL2 growth, indicating no autocrine impact of growth factors produced by HIF-1α stabilization. Furthermore, in normoxia, CtL2 infection changed the NAD⁺/NADH ratio of cells with increased gapdh expression; in contrast, under hypoxia, the NAD⁺/NADH ratio was the same in infected and uninfected cells with high and stable expression of gapdh, suggesting that CtL2-infected cells adapted better to hypoxia. Together, these data indicate that hypoxia promotes CtL2 growth in immortal human epithelial cells by activating the PI3K-AKT pathway and maintaining the NAD⁺/NADH ratio with stably activated glycolysis.

Comparison of In Vitro Chlamydia muridarum Infection Under Aerobic and Anaerobic Conditions

Although Chlamydia infects host body regions that are hypoxic to anoxic, standard Chlamydiae culture conditions are in CO₂ enriched (5%) atmospheric oxygen (21%). Because of its success in causing disease in principally anaerobic body sites, e.g., vaginal tract, we hypothesize that Chlamydia has an anaerobic life cycle that plays a role in its maintenance in the host. Using a model system developed for the anaerobic culture of mammalian cells, we assessed the anoxic infectious cycle of C. muridarum in anaerobically cultured HeLa 229 cells. In the absence of oxygen, C. muridarum is capable of going through their life cycle, although its cycle is slowed (2 days post-infection anaerobic vs. 1 day aerobic). Interestingly, in addition to a slower rate of replication, there is a reduction in Chlamydia inclusion number and size as compared to aerobic controls. Anaerobic infected host cell physiology also changed with IL-6 and IL-8 production significantly lower (p ≤ 0.05) compared to aerobic infected host cells (day 4 post-infection). These findings demonstrate that Chlamydia are capable of replicating in the absence of oxygen.

Elaborations on Corallopyronin A as a Novel Treatment Strategy Against Genital Chlamydial Infections

Ascending Chlamydia trachomatis infection causes functional damage to the fallopian tubes, which may lead to ectopic pregnancy and infertility in women. Treatment failures using the standard regimens of doxycycline and azithromycin have been observed. We tested the polyketide-derived α-pyrone antibiotic Corallopyronin A (CorA) that inhibits the bacterial DNA dependent RNA polymerase and has strong activity against various extracellular and some intracellular bacteria. Extensive testing in cell culture infection models and in an ex vivo human fallopian tube model under different oxygen concentrations was performed to assess the anti-chlamydial efficacy of CorA at physiological conditions. CorA showed high efficacy against C. trachomatis (MIC_N/H: 0.5 μg/mL for serovar D and L2), C. muridarum (MIC_N/H: 0.5 μg/mL), and C. pneumoniae (MIC_N/H: 1 μg/mL) under normoxic (N) and hypoxic (H) conditions. Recoverable inclusion forming units were significantly lower already at 0.25 μg/mL for all tested chlamydiae. CorA at a concentration of 1 μg/mL was also effective against already established C. trachomatis and C. pneumoniae infections (up to 24 h.p.i.) in epithelial cells, while efficacy against C. muridarum was limited to earlier time points. A preliminary study using a C. muridarum genital infection model revealed corresponding limitations in the efficacy. Importantly, in an ex vivo human fallopian tube model, the growth of C. trachomatis was significantly inhibited by CorA at concentrations of 1–2 μg/mL under normoxic and hypoxic conditions. The overall high efficacies of CorA against C. trachomatis in cell culture and an ex vivo human fallopian tube model under physiological oxygen concentrations qualifies this drug as a candidate that should be further investigated.

Novel Detection Strategy To Rapidly Evaluate the Efficacy of Antichlamydial Agents

Chlamydia trachomatis infections present a major heath burden worldwide. The conventional method used to detect C. trachomatis is laborious. In the present study, a novel strategy was utilized to evaluate the impact of antimicrobial agents on the growth of C. trachomatis and its expression of ompA promoter-driven green fluorescence protein (GFP). We demonstrate that this GFP reporter system gives a robust fluorescent display of C. trachomatis growth in human cervical epithelial cells and, further, that GFP production directly correlates to changes in ompA expression following sufficient exposure to antimicrobials. Validation with azithromycin, the first-line macrolide drug used for the treatment of C. trachomatis infection, highlights the advantages of this method over the traditional method because of its simplicity and versatility. The results indicate both that ompA is highly responsive to antimicrobials targeting the transcription and translation of C. trachomatis and that there is a correlation between changing GFP levels and C. trachomatis growth. This proof-of-concept study also reveals that the ompA-GFP system can be easily adapted to rapidly assess antimicrobial effectiveness in a high-throughput format.

Evaluating the Effect of Oxygen Concentrations on Antibiotic Sensitivity, Growth, and Biofilm Formation of Human Pathogens

Standard antimicrobial susceptibility tests are performed in vitro under normal room oxygen conditions to predict the in vivo effectiveness of antimicrobial therapy. The aim of this study was to conduct a comprehensive analysis of the effect of different oxygen levels on the antibiotic susceptibility of two strains of Staphylococcus aureus, Pseudomonas aeruginosa, and Klebsiella pneumoniae. It was found that anoxic conditions caused reduced sensitivity of bacteria to aminoglycoside antibiotics in four of six bacteria used in the study. In addition, oxygen limitation decreased the susceptibility of P. aeruginosa strains and K. pneumoniae strains to piperacillin/tazobactam and azithromycin, respectively. In contrast, five of six bacteria became more susceptible to tetracycline antibiotics under oxygen-limiting conditions. Our data highlight the importance of considering the potential in vivo oxygen levels within the infection site when setting susceptibility breakpoints for evaluating the therapeutic potential of a drug and its effect on antibiotic sensitivity of the pathogen.

Preventing Data Ambiguity in Infectious Diseases with Four-Dimensional and Personalized Evaluations

Background

Diagnostic errors can occur, in infectious diseases, when anti-microbial immune responses involve several temporal scales. When responses span from nanosecond to week and larger temporal scales, any pre-selected temporal scale is likely to miss some (faster or slower) responses. Hoping to prevent diagnostic errors, a pilot study was conducted to evaluate a four-dimensional (4D) method that captures the complexity and dynamics of infectious diseases.

Methods

Leukocyte-microbial-temporal data were explored in canine and human (bacterial and/or viral) infections, with: (i) a non-structured approach, which measures leukocytes or microbes in isolation; and (ii) a structured method that assesses numerous combinations of interacting variables. Four alternatives of the structured method were tested: (i) a noise-reduction oriented version, which generates a single (one data point-wide) line of observations; (ii) a version that measures complex, three-dimensional (3D) data interactions; (iii) a non-numerical version that displays temporal data directionality (arrows that connect pairs of consecutive observations); and (iv) a full 4D (single line-, complexity-, directionality-based) version.

Results

In all studies, the non-structured approach revealed non-interpretable (ambiguous) data: observations numerically similar expressed different biological conditions, such as recovery and lack of recovery from infections. Ambiguity was also found when the data were structured as single lines. In contrast, two or more data subsets were distinguished and ambiguity was avoided when the data were structured as complex, 3D, single lines and, in addition, temporal data directionality was determined. The 4D method detected, even within one day, changes in immune profiles that occurred after antibiotics were prescribed.

Conclusions

Infectious disease data may be ambiguous. Four-dimensional methods may prevent ambiguity, providing earlier, in vivo, dynamic, complex, and personalized information that facilitates both diagnostics and selection or evaluation of anti-microbial therapies.

Chlamydial Antibiotic Resistance and Treatment Failure in Veterinary and Human Medicine

The Chlamydiaceae are widespread pathogens of both humans and animals. Chlamydia trachomatis infection causes blinding trachoma and reproductive complications in humans. Chlamydia pneumoniae causes human respiratory tract infections and atypical pneumonia. Chlamydia suis infection is associated with conjunctivitis, diarrhea, and failure to gain weight in domestic swine. Chlamydial infections in humans and domesticated animals are generally controlled by antibiotic treatment—particularly macrolides (usually azithromycin) and tetracyclines (tetracycline and doxycycline). Tetracycline-containing feed has also been used to limit infections and promote growth in livestock populations, although its use has decreased because of growing concerns about antimicrobial resistance development. Because Sandoz and Rockey published an elegant review of chlamydial anti-microbial resistance in 2010, we will review the following: (i) antibiotic resistance in C. suis, (ii) recent evidence for acquired resistance in human chlamydial infections, and (iii) recent non-genetic mechanisms of antibiotic resistance that may contribute to treatment failure.

High dynamic range detection of Chlamydia trachomatis growth by direct quantitative PCR of the infected cells

Chlamydiae are obligate intracellular bacteria developing in an intracytoplasmic niche, the inclusion. Chlamydia growth measurement by inclusion counting is a key task in the development of novel antichlamydial antibiotics and in vaccine studies. Most of the current counting methods rely on the immunofluorescent staining of the inclusions and either manual or automatic microscopy detection and enumeration. The manual method is highly labor intensive, while the automatic methods are either medium-throughput or require automatic microscopy. The sensitive and specific PCR technology could be an effective method for growth related chlamydial DNA detection; however the currently described PCR approaches have a major limitation, the requirement of purification of DNA or RNA from the infected cells. This limitation makes this approach unfeasible for high-throughput screenings. To overcome this, we developed a quantitative PCR (qPCR) method for the detection of Chlamydia trachomatis DNA directly from the infected HeLa cells. With our method we were able to detect the bacterial growth in a 4 log scale (multiplicity of infection (MOI): 64 to 0.0039), with high correlation between the biological and technical replicates. As a further proof of the method, we applied the direct qPCR for antibiotic minimum inhibitory concentration (MIC) measurements. The measured MICs of moxifloxacin, tetracycline, clarithromycin and compound PCC00213 were 0.031 μg/ml, 0.031 μg/ml, 0.0039 μg/ml and 6.2 μg/ml respectively, identical or close to the already published MIC values. Our direct qPCR method for chlamydial growth and antibiotic MIC determination is less time-consuming, more objective and more sensitive than the currently applied manual or automatic fluorescent microscopy- based methods.

Inhibitory activity of the isoflavone biochanin A on intracellular bacteria of genus Chlamydia and initial development of a buccal formulation

Given the established role of Chlamydia spp. as causative agents of both acute and chronic diseases, search for new antimicrobial agents against these intracellular bacteria is required to promote human health. Isoflavones are naturally occurring phytoestrogens, antioxidants and efflux pump inhibitors, but their therapeutic use is limited by poor water-solubility and intense first-pass metabolism. Here, we report on effects of isoflavones against C. pneumoniae and C. trachomatis and describe buccal permeability and initial formulation development for biochanin A. Biochanin A was the most potent Chlamydia growth inhibitor among the studied isoflavones, with an IC₅₀ = 12 µM on C. pneumoniae inclusion counts and 6.5 µM on infectious progeny production, both determined by immunofluorescent staining of infected epithelial cell cultures. Encouraged by the permeation of biochanin A across porcine buccal mucosa without detectable metabolism, oromucosal film formulations were designed and prepared by a solvent casting method. The film formulations showed improved dissolution rate of biochanin A compared to powder or a physical mixture, presumably due to the solubilizing effect of hydrophilic additives and presence of biochanin A in amorphous state. In summary, biochanin A is a potent inhibitor of Chlamydia spp., and the in vitro dissolution results support the use of a buccal formulation to potentially improve its bioavailability in antichlamydial or other pharmaceutical applications.

Application of DNA chip scanning technology for automatic detection of Chlamydia trachomatis and Chlamydia pneumoniae inclusions

Chlamydiae are obligate intracellular bacteria that propagate in the inclusion, a specific niche inside the host cell. The standard method for counting chlamydiae is immunofluorescent staining and manual counting of chlamydial inclusions. High- or medium-throughput estimation of the reduction in chlamydial inclusions should be the basis of testing antichlamydial compounds and other drugs that positively or negatively influence chlamydial growth, yet low-throughput manual counting is the common approach. To overcome the time-consuming and subjective manual counting, we developed an automatic inclusion-counting system based on a commercially available DNA chip scanner. Fluorescently labeled inclusions are detected by the scanner, and the image is processed by ChlamyCount, a custom plug-in of the ImageJ software environment. ChlamyCount was able to measure the inclusion counts over a 1-log-unit dynamic range with a high correlation to the theoretical counts. ChlamyCount was capable of accurately determining the MICs of the novel antimicrobial compound PCC00213 and the already known antichlamydial antibiotics moxifloxacin and tetracycline. ChlamyCount was also able to measure the chlamydial growth-altering effect of drugs that influence host-bacterium interaction, such as gamma interferon, DEAE-dextran, and cycloheximide. ChlamyCount is an easily adaptable system for testing antichlamydial antimicrobials and other compounds that influence Chlamydia-host interactions.

Activities of first-choice antimicrobials against gamma interferon-treated Chlamydia trachomatis differ in hypoxia

Gamma interferon (IFN-γ)-mediated host responses play a central role in resolving genital Chlamydia trachomatis infections but may also result in persistence of the pathogen, which shows reduced susceptibility to antimicrobials. The antichlamydial function of IFN-γ is oxygen dependent, and the efficacy of antimicrobials against C. trachomatis is reduced in a low-oxygen environment. In this study, we show that the antichlamydial efficacies of azithromycin and doxycycline differ in IFN-γ-treated cells under hypoxia.

Chlamydia-induced ReA: immune imbalances and persistent pathogens

Reactive arthritis (ReA), an inflammatory arthritic condition that is commonly associated with Chlamydia infections, represents a significant health burden, yet is poorly understood. The enigma of this disease is reflected in its problematic name and in its ill-defined pathogenesis. The existence of persistent pathogens in the arthritic joint is acknowledged, but their relevance remains elusive. Progress is being made in understanding the underlying mechanisms of ReA, whereby an imbalance between type 1 and type 2 immune responses seems to be critical in determining susceptibility to disease. Such an imbalance occurs prior to the initiation of an adaptive immune response, suggesting that innate cellular and molecular mechanisms in ReA should be prioritized as fruitful areas for investigation.

When oxygen runs short: the microenvironment drives host-pathogen interactions

Pathogens that colonize or infect the human body have to face varying oxygen concentrations within different organs. Inflammation itself promotes oxygen consumption within affected tissues and creates a low oxygen environment. As a consequence, pathogens and the host immune system have to adapt to rapid changes in oxygen availability. Here we summarize recent findings on the adaptation of pathogens, host defense mechanisms and treatment strategies against intracellular pathogens in a low oxygen environment.