Chlamydia Serine Protease Inhibitor, targeting HtrA, as a New Treatment for Koala Chlamydia infection

Epidemiology, Transmission Mode, and Pathogenesis of Chlamydia pecorum Infection in Koalas (Phascolarctos cinereus): An Overview

Chlamydial infections pose a significant threat to koala populations. Chlamydia pecorum (C. pecorum) remains the major chlamydial species affecting koala health, both in the wild and in captivity, and chlamydial infections are considered important factors affecting the long-term survival of koalas. A clear understanding of chlamydial infections, including the epidemiology, transmission mode, pathogenesis, immune response, control, and prevention thereof, is essential for improving the management of chlamydial infections in koalas. In this study, we discuss the important advances made in our understanding of C. pecorum infection in koalas, focusing on the epidemiology of chlamydial infections, and the transmission, pathogenesis, immune response, and control strategies for chlamydial infection, with the aim of improving koala health and achieving effective conservation strategies.

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.

Evaluation of a biosecurity survey approach for contamination by Chlamydia pecorum in koala rehabilitation, field capture, and captive settings

Transmission of Chlamydia pecorum between koalas is a potential risk in field capture or rehabilitation settings, where koalas are held in proximity to each other, or equipment is shared between animals. Given the impact of C. pecorum on koala welfare and population viability it is surprising that quarantine and disinfection protocols in a koala rehabilitation facility or capture settings have not previously been evaluated. This study aimed to evaluate an approach, based on the detection of chlamydial DNA and cell viability, to determine the degree of environmental contamination within a koala care facility. Various fomite sites associated with koala care at a koala rehabilitation facility in New South Wales, Australia were identified as potential sources of chlamydial contamination, following exposure to koalas known to be infected with C. pecorum. Fomite sites were swabbed following exposure, and again after decontamination procedures were carried out. Samples were tested for the presence of chlamydial DNA using qPCR and viability using both RT-qPCR and cell culture. From a total of 239 sampling events, 30 tested qPCR positive for chlamydial DNA, with 19 and 11 samples corresponding to pre-decontamination and post-decontamination events respectively. Detection of chlamydial DNA appeared to be most common in the examination room, especially on fomite sites in direct contact with koalas. Physical removal of chlamydial DNA, or its degradation by the elements, appeared to be more common on outdoor enclosures, clothing, and hands. Based on the cell culture assay, of the pre-decontamination samples with chlamydial DNA, eight had viable chlamydial cells, two of these at low levels. Of the post-decontamination samples with chlamydial DNA, one had a moderate number, and one had a very low number of viable chlamydial cells. RT-qPCR was unsuccessful in determining cell viability due to low yields of RNA and high levels of contaminants from the environmental samples. The outcomes of this study provide a knowledge base for the design of future biosecurity evaluation guidelines in captive and koala rehabilitation facilities. The higher incidence of chlamydial DNA detection by qPCR than viable organism highlights the need to use viability assays in similar studies. However, further investment is still needed to optimise these methods and improve sensitivity for complex environmental samples.

Design, Biological Evaluation, and Computer-Aided Analysis of Dihydrothiazepines as Selective Antichlamydial Agents

Chlamydia trachomatis (CT) causes the most prevalent sexually transmitted bacterial disease in the United States. The lack of drug selectivity is one of the main challenges of the current antichlamydial pharmacotherapy. The metabolic needs of CT are controlled, among others, by cylindrical proteases and their chaperones (e.g., ClpX). It has been shown that dihydrothiazepines can disrupt CT-ClpXP. Based on this precedent, we synthesized a dihydrothiazepine library and characterized its antichlamydial activity using a modified semi-high-throughput screening assay. Then, we demonstrated their ability to inhibit ClpX ATPase activity in vitro, supporting ClpX as a target. Further, our lead compound displayed a promising selectivity profile against CT, acceptable cytotoxicity, no mutagenic potential, and good in vitro stability. A two-dimensional quantitative structure-activity relationship (2D QSAR) model was generated as a support tool in the identification of more potent antichlamydial molecules. This study suggests dihydrothiazepines are a promising starting point for the development of new and selective antichlamydial drugs.

Improving Antibacterial Activity of a HtrA Protease Inhibitor JO146 against Helicobacter pylori: A Novel Approach Using Microfluidics-Engineered PLGA Nanoparticles

Nanoparticle drug delivery systems have emerged as a promising strategy for overcoming limitations of antimicrobial drugs such as stability, bioavailability, and insufficient exposure to the hard-to-reach bacterial drug targets. Although size is a vital colloidal feature of nanoparticles that governs biological interactions, the absence of well-defined size control technology has hampered the investigation of optimal nanoparticle size for targeting bacterial cells. Previously, we identified a lead antichlamydial compound JO146 against the high temperature requirement A (HtrA) protease, a promising antibacterial target involved in protein quality control and virulence. Here, we reveal that JO146 was active against Helicobacter pylori with a minimum bactericidal concentration of 18.8–75.2 µg/mL. Microfluidic technology using a design of experiments approach was utilized to formulate JO146-loaded poly(lactic-co-glycolic) acid nanoparticles and explore the effect of the nanoparticle size on drug delivery. JO146-loaded nanoparticles of three different sizes (90, 150, and 220 nm) were formulated with uniform particle size distribution and drug encapsulation efficiency of up to 25%. In in vitro microdilution inhibition assays, 90 nm nanoparticles improved the minimum bactericidal concentration of JO146 two-fold against H. pylori compared to the free drug alone, highlighting that controlled engineering of nanoparticle size is important in drug delivery optimization.

Design, synthesis and biological evaluation of P2-modified proline analogues targeting the HtrA serine protease in Chlamydia

High temperature requirement A (HtrA) serine proteases have emerged as a novel class of antibacterial target, which are crucial in protein quality control and are involved in the pathogenesis of a wide array of bacterial infections. Previously, we demonstrated that HtrA in Chlamydia is essential for bacterial survival, replication and virulence. Here, we report a new series of proline (P2)-modified inhibitors of Chlamydia trachomatis HtrA (CtHtrA) developed by proline ring expansion and Cγ-substitutions. The structure-based drug optimization process was guided by molecular modelling and in vitro pharmacological evaluation of inhibitory potency, selectivity and cytotoxicity. Compound 25 from the first-generation 4-substituted proline analogues increased antiCtHtrA potency and selectivity over human neutrophil elastase (HNE) by approximately 6- and 12-fold, respectively, relative to the peptidic lead compound 1. Based on this compound, second-generation substituted proline residues containing 1,2,3-triazole moieties were synthesized by regioselective azide-alkyne click chemistry. Compound 49 demonstrated significantly improved antichlamydial activity in whole cell assays, diminishing the bacterial infectious progeny below the detection limit at the lowest dose tested. Compound 49 resulted in approximately 9- and 22-fold improvement in the inhibitory potency and selectivity relative to 1, respectively. To date, compound 49 is the most potent HtrA inhibitor developed against Chlamydia spp.

Completing the Genome Sequence of Chlamydia pecorum Strains MC/MarsBar and DBDeUG: New Insights into This Enigmatic Koala (Phascolarctos cinereus) Pathogen

Chlamydia pecorum, an obligate intracellular pathogen, causes significant morbidity and mortality in livestock and the koala (Phascolarctos cinereus). A variety of C. pecorum gene-centric molecular studies have revealed important observations about infection dynamics and genetic diversity in both koala and livestock hosts. In contrast to a variety of C. pecorum molecular studies, to date, only four complete and 16 draft genomes have been published. Of those, only five draft genomes are from koalas. Here, using whole-genome sequencing and a comparative genomics approach, we describe the first two complete C. pecorum genomes collected from diseased koalas. A de novo assembly of DBDeUG_2018 and MC/MarsBar_2018 resolved the chromosomes and chlamydial plasmids each as single, circular contigs. Robust phylogenomic analyses indicate biogeographical separation between strains from northern and southern koala populations, and between strains infecting koala and livestock hosts. Comparative genomics between koala strains identified new, unique, and shared loci that accumulate single-nucleotide polymorphisms and separate between northern and southern, and within northern koala strains. Furthermore, we predicted novel type III secretion system effectors. This investigation constitutes a comprehensive genome-wide comparison between C. pecorum from koalas and provides improvements to annotations of a C. pecorum reference genome. These findings lay the foundations for identifying and understanding host specificity and adaptation behind chlamydial infections affecting koalas.

Targeted Protein Degradation: The New Frontier of Antimicrobial Discovery?

Targeted protein degradation aims to hijack endogenous protein quality control systems to achieve direct knockdown of protein targets. This exciting technology utilizes event-based pharmacology to produce therapeutic outcomes, a feature that distinguishes it from classical occupancy-based inhibitor agents. Early degrader candidates display resilience to mutations while possessing potent nanomolar activity and high target specificity. Paired with the rapid advancement of our knowledge in the factors driving targeted degradation, the expansion of this style of therapeutic agent to a range of disease indications is eagerly awaited. In particular, the area of antibiotic discovery is sorely lacking in novel approaches, with the Antimicrobial Resistance (AMR) crisis looming as the next potential global health calamity. Here, the current advances in targeted protein degradation are highlighted, and potential approaches for designing novel antimicrobial protein degraders are proposed, ranging from adaptations of current strategies to completely novel approaches to targeted protein degradation.

Optimization of peptide-based inhibitors targeting the HtrA serine protease in Chlamydia: Design, synthesis and biological evaluation of pyridone-based and N-Capping group-modified analogues

The obligate intracellular bacterium Chlamydia trachomatis (C. trachomatis) is responsible for the most common bacterial sexually transmitted infection and is the leading cause of preventable blindness, representing a major global health burden. While C. trachomatis infection is currently treatable with broad-spectrum antibiotics, there would be many benefits of a chlamydia-specific therapy. Previously, we have identified a small-molecule lead compound JO146 [Boc-Val-Pro-Val^P(OPh)₂] targeting the bacterial serine protease HtrA, which is essential in bacterial replication, virulence and survival, particularly under stress conditions. JO146 is highly efficacious in attenuating infectivity of both human (C. trachomatis) as well as koala (C. pecorum) species in vitro and in vivo, without host cell toxicity. Herein, we present our continuing efforts on optimizing JO146 by modifying the N-capping group as well as replacing the parent peptide structure with the 2-pyridone scaffold at P3/P2. The drug optimization process was guided by molecular modelling, enzyme and cell-based assays. Compound 18b from the pyridone series showed improved inhibitory activity against CtHtrA by 5-fold and selectivity over human neutrophil elastase (HNE) by 109-fold compared to JO146, indicating that 2-pyridone is a suitable bioisostere of the P3/P2 amide/proline for developing CtHtrA inhibitors. Most pyridone-based inhibitors showed superior anti-chlamydial potency to JO146 especially at lower doses (25 and 50 μM) in C. trachomatis and C. pecorum cell culture assays. Modifications of the N-capping group of the peptidyl inhibitors did not have much influence on the anti-chlamydial activities, providing opportunities for more versatile alterations and future optimization. In summary, we present 2-pyridone based analogues as a new generation of non-peptidic CtHtrA inhibitors, which hold better promise as anti-chlamydial drug candidates.

Koala cathelicidin PhciCath5 has antimicrobial activity, including against Chlamydia pecorum

Devastating fires in Australia over 2019-20 decimated native fauna and flora, including koalas. The resulting population bottleneck, combined with significant loss of habitat, increases the vulnerability of remaining koala populations to threats which include disease. Chlamydia is one disease which causes significant morbidity and mortality in koalas. The predominant pathogenic species, Chlamydia pecorum, causes severe ocular, urogenital and reproductive tract disease. In marsupials, including the koala, gene expansions of an antimicrobial peptide family known as cathelicidins have enabled protection of immunologically naïve pouch young during early development. We propose that koala cathelicidins are active against Chlamydia and other bacteria and fungi. Here we describe ten koala cathelicidins, five of which contained full length coding sequences that were widely expressed in tissues throughout the body. Focusing on these five, we investigate their antimicrobial activity against two koala C. pecorum isolates from distinct serovars; MarsBar and IPTaLE, as well as other bacteria and fungi. One cathelicidin, PhciCath5, inactivated C. pecorum IPTaLE and MarsBar elementary bodies and significantly reduced the number of inclusions compared to the control (p<0.0001). Despite evidence of cathelicidin expression within tissues known to be infected by Chlamydia, natural PhciCath5 concentrations may be inadequate in vivo to prevent or control C. pecorum infections in koalas. PhciCath5 also displayed antimicrobial activity against fungi and Gram negative and positive bacteria, including methicillin-resistant Staphylococcus aureus (MRSA). Electrostatic interactions likely drive PhciCath5 adherence to the pathogen cell membrane, followed by membrane permeabilisation leading to cell death. Activity against E. coli was reduced in the presence of 10% serum and 20% whole blood. Future modification of the PhciCath5 peptide to enhance activity, including in the presence of serum/blood, may provide a novel solution to Chlamydia infection in koalas and other species.

A 29-year retrospective analysis of koala rescues in New South Wales, Australia

The koala (Phascolarctos cinereus) is currently listed by both the IUCN and the Australian Governments' Threatened Species Scientific Committee as vulnerable to extinction with an overall decreasing population trend. It is unknown exactly how many koalas remain in the wild, but it is known that habitat fragmentation and bushfires have ultimately contributed to the decline of the koala all over Australia. This novel study is a retrospective analysis of data over a 29-year period (1989-2018) using records for 12,543 sightings and clinical care admissions for wild koalas from the major koala hot-spots (Port Stephens, port Macquarie and Lismore) in New South Wales, Australia. This study aims to understand the long-term patterns and trends of key stressors that are contributing to the decline of koalas in New South Wales, and the synergic interactions of factors such as rescue location, sex and age of the koala, and if their decline is influenced progressively by year. The main findings of this retrospective analysis indicated that between all 3 rescue sites, the most common prognosis was disease, the most common disease was signs of chlamydia, and the most common outcome was release. The location where the highest number of koalas were found prior to being reported as sighted or admitted into clinical care was within the regional area of Lismore. Furthermore, sex was not a discriminating factor when it came to prognosis or outcome, but age was significant. Finally, incidents of disease were found to increase over long-term, whereas release decreased over time and euthanasia increased. The wealth of data available to us and the retrospective analysis enabled us in a way to 'zoom out' and reveal how the key environmental stressors have fluctuated spatially and temporally. In conclusion, our data provides strong evidence of added pressures of increased human population growth in metropolitan zones, which increases risks of acute environmental trauma and proximate stressors such as vehicle collisions and dog-attacks as well as increased sightings of virtually healthy koalas found in exposed environments. Thus our 'zoom out' approach provides support that there is an urgent need to strengthen on-ground management, bushfire control regimes, environmental planning and governmental policy actions that should hopefully reduce the proximate environmental stressors in a step wise approach. This will ensure that in the next decade (beyond 2020), NSW koalas will hopefully start to show reversed trends and patterns in exposure to environmental trauma and disease, and population numbers will return towards recovery and stability.

Helping koalas battle disease - Recent advances in Chlamydia and koala retrovirus (KoRV) disease understanding and treatment in koalas

The iconic Australian marsupial, the koala (Phascolarctos cinereus), has suffered dramatic population declines as a result of habitat loss and fragmentation, disease, vehicle collision mortality, dog attacks, bushfires and climate change. In 2012, koalas were officially declared vulnerable by the Australian government and listed as a threatened species. In response, research into diseases affecting koalas has expanded rapidly. The two major pathogens affecting koalas are Chlamydia pecorum, leading to chlamydial disease and koala retrovirus (KoRV). In the last eight years, these pathogens and their diseases have received focused study regarding their sources, genetics, prevalence, disease presentation and transmission. This has led to vast improvements in pathogen detection and treatment, including the ongoing development of vaccines for each as a management and control strategy. This review will summarize and highlight the important advances made in understanding and combating C. pecorum and KoRV in koalas, since they were declared a threatened species. With complementary advances having also been made from the koala genome sequence and in our understanding of the koala immune system, we are primed to make a significant positive impact on koala health into the future.

Chlamydiae from Down Under: The Curious Cases of Chlamydial Infections in Australia

In Australia, the most researched and perhaps the most successful chlamydial species are the human pathogen Chlamydia trachomatis, animal pathogens Chlamydia pecorum and Chlamydia psittaci. C. trachomatis remains the leading cause of sexually transmitted infections in Australians and trachoma in Australian Indigenous populations. C. pecorum is globally recognised as the infamous koala and widespread livestock pathogen, whilst the avian C. psittaci is emerging as a horse pathogen posing zoonotic risks to humans. Certainly not innocuous, the human infections with Chlamydia pneumoniae seem to be less prevalent that other human chlamydial pathogens (namely C. trachomatis). Interestingly, the complete host range for C. pecorum and C. psittaci remains unknown, and infections by other chlamydial organisms in Australian domesticated and wildlife animals are understudied. Considering that chlamydial organisms can be encountered by either host at the human/animal interface, I review the most recent findings of chlamydial organisms infecting Australians, domesticated animals and native wildlife. Furthermore, I also provide commentary from leading Australian Chlamydia experts on challenges and future directions in the Chlamydia research field.

Longitudinal study of wild koalas (Phascolarctos cinereus) reveals chlamydial disease progression in two thirds of infected animals

Chlamydial disease threatens many of Australia’s koala populations, and yet our understanding of chlamydial epidemiology and disease dynamics in koalas is limited by a lack of comprehensive, longitudinal population studies. To address this, we utilised longitudinal samples from a large-scale population study of wild koalas in south-east Queensland, to follow chlamydial infections over time and to investigate some of the drivers of disease progression. Our findings show, firstly, that almost two thirds of chlamydial infections progressed to disease, challenging the notion that chlamydial infections in koalas commonly remain chronic and asymptomatic. Secondly, disease progression at the urogenital tract site was associated with infection load, and urogenital tract shedding was significantly higher when koalas acquired a new infection. Thirdly, chronic chlamydial exposure was not necessary for pathogenic sequelae to develop, such as infertility and mortality. Fourthly, ompA-characterised strain sub-types may reflect tissue tropisms and pathogenicity, and the chlamydial status of some chronically infected koalas may be explained by reinfections with novel genotypes. Finally, successful antimicrobial treatment provided only short-term protection against reinfection and disease progression in susceptible koalas. These findings highlight the importance of identifying and preventing chlamydial infections in koalas, informing new population management strategies and research priorities.

Antibiotic treatment of Chlamydia-induced cystitis in the koala is linked to expression of key inflammatory genes in reactive oxygen pathways

Chlamydial-induced cystitis in the koala (Phascolarctos cinereus) is currently treated by antibiotics. However, while reducing the chlamydial load, this treatment can also lead to gastrointestinal complications and death. Development of alternative treatments, such as a therapeutic chlamydial vaccine, are hindered by the lack of detailed understanding of the innate immune response to chlamydial clearance and disease regression during antibiotic treatment. Through clinical, microbiological and transcriptomic approaches, disease regression, bacterial clearance and innate immune responses were mapped in koalas with signs of chlamydial-induced cystitis while receiving anti-chlamydial antibiotics. Significant reduction in the signs of cystitis were observed during and post antibiotic treatment. This was observed as a thinning of the bladder wall and complete reversal of urinary incontinence. Transcriptomic analysis before treatment, at the end of treatment and prior to release identified significant down-regulation of specific genes involved in 21 biological pathways. Of these, the chemokine receptor signalling and NOD-like receptor signalling pathways where identified as important markers of inflammation. Specific genes within these pathways (NCF1 and NOX2) were significantly down-regulated, suggesting a decrease in reactive oxygen species production. Through the monitoring of specific clinical and transcriptomic markers, these findings allow detailed profiling of the clinical response to therapeutic vaccination in koalas with current signs of disease. This also adds to our understanding of innate immune responses to chlamydial infections and indicates that chlamydial-induced cystitis in the koala is linked to the regulation of reactive oxygen pathways.

A novel protease inhibitor causes inclusion vacuole reduction and disrupts the intracellular growth of Chlamydia trachomatis

Chlamydia (C.) trachomatis, characterized by a unique biphasic life cycle, is an obligate intracellular bacterial pathogen which is responsible for the highest number of sexually transmitted bacterial infections globally. However, its pathogenic mechanisms have not been fully elucidated because of its unique developmental cycle and obligate intracellular nature. High temperature requirement (HtrA), a critical protease and chaperone, has been previously demonstrated to be essential for several functions and the replicative phase in the C. trachomatis developmental cycle. In the current study, we designed and synthesized a novel peptidomimetic inhibitor targeting C. trachomatis HtrA (CtHtrA) using homology modeling and chemical synthesis. The inhibitor was tested in chlamydia in the mid-replicative phase and resulted in a significant loss of viable infectious progeny and diminishing inclusion size and number at a relatively low concentration. This finding not only indicates that CtHtrA plays a critical role during the replicative phase of the chlamydial developmental cycle but also reveals a useful target for the design of novel anti-chlamydial agents.

Quantification of serine protease HtrA molecules secreted by the foodborne pathogen Campylobacter jejuni

BACKGROUND

Campylobacter jejuni is a major food-borne pathogen and a worldwide health threat. Utilizing different virulence factors, C. jejuni invades the host's intestinal epithelial cell layer. One important factor in this process is the serine protease HtrA, which is secreted into the extracellular space, and helps the bacteria to transmigrate across the gut epithelium by cleaving various cell-cell adhesion proteins. The aim of the present study is to quantify the amount of HtrA molecules secreted per bacterial cell in liquid culture and during infection.

RESULTS

HtrA protein purification and quantitative Western blotting were used to determine the number of HtrA molecules secreted by two C. jejuni model strains, 11168 and 81-176, in liquid culture during an 8-h time course. On average, the two strains yielded similar HtrA secretion rates, with strain 11168 secreting 4314 ± 949 molecules and 81-176 secreting 5483 ± 1246 per bacterium after 2 h. After 8 h, both strains showed a decrease in the average amount of HtrA secreted per bacterial cell over time. Secretion of HtrA by strain 11168 reduced to about 1772 ± 520 molecules and only 2151 ± 562 HtrA molecules were secreted by strain 81-176 at this time point. During infection of gut epithelial cells, the secretion of HtrA is slightly higher with a similar secretion pattern over time compared to culturing in vitro.

CONCLUSION

We determined the number of HtrA molecules secreted by single C. jejuni cells over time. The results suggest that HtrA secretion is regulated in a time-dependent fashion, leading to increasing accumulative HtrA concentrations in the extracellular medium.

Mini Review: Antimicrobial Control of Chlamydial Infections in Animals: Current Practices and Issues

Chlamydia are a genus of successful obligate intracellular pathogens spread across humans, wildlife, and domesticated animals. The most common species reported in livestock in this genus are Chlamydia abortus, Chlamydia psittaci, Chlamydia suis, and Chlamydia pecorum. Chlamydial infections trigger a series of inflammatory disease-related sequelae including arthritis, conjunctivitis, pneumonia, and abortion. Other bacteria in the phylum Chlamydiae have also been reported in livestock and wildlife but their impact on animal health is less clear. Control of chlamydial infections relies on the use of macrolides, fluoroquinolones, and tetracyclines. Tetracycline resistance (TET^R) reported for porcine C. suis strains in association with the use of tetracycline feed is a potentially significant concern given experimental evidence highlighting that the genetic elements inferring TET^R may be horizontally transferred to other chlamydial species. As documented in human Chlamydia trachomatis infections, relapse of infections, bacterial shedding post-antibiotic treatment, and disease progression despite chlamydial clearance in animals have also been reported. The identification of novel chlamydiae as well as new animal hosts for previously described chlamydial pathogens should place a renewed emphasis on basic in vivo studies to demonstrate the efficacy of existing and new antimicrobial treatment regimes. Building on recent reviews of antimicrobials limited to C. trachomatis and C. suis, this review will explore the use of antimicrobials, the evidence and factors that influence the treatment failure of chlamydial infections in animals and the future directions in the control of these important veterinary pathogens.

Optimising the short and long-term clinical outcomes for koalas (Phascolarctos cinereus) during treatment for chlamydial infection and disease

Koalas (Phascolarctos cinereus) have suffered severe declines in the northern extent of their range due to a variety of threats, including habitat destruction, trauma from cars and dogs, climate change and importantly, disease. The most significant pathogen in koalas is Chlamydia pecorum, which causes inflammation and fibrosis at mucosal sites, resulting in blindness, infertility and death in severe cases. Chlamydia treatment can be problematic in koalas as the response to treatment is often poor in chronic cases and antimicrobial choice is limited. Thus, chlamydial disease is a severely threatening process for koala conservation. We investigated the short and long-term clinical outcomes for 167 koalas with Chlamydia that underwent capture, telemetric monitoring and intensive veterinary management as part of a large-scale population management program in South East Queensland. Chlamydia treatments included the standard regimen of daily subcutaneous chloramphenicol injections (60mg/kg) for 14 to 28-days, and a variety of non-standard regimens such as topical antimicrobials only (for ocular disease), surgical treatment only (for bilateral reproductive tract disease), and other antimicrobials/treatment lengths. To assess these regimens we analysed clinical records, field monitoring data and swab samples collected from the urogenital tract and ocular conjunctiva. Overall, in contrast to other studies, treatment was generally successful with 86.3% of treated koalas released back into the wild. The success of treatment rose to 94.8% however, when the standard treatment regimen was employed. Further, 100% of koalas that were also treated with surgical ovariohysterectomy (n = 12) remained healthy for a median of 466 days of post-treatment monitoring, demonstrating the benefits of surgical treatment. Previous studies reported 45-day chloramphenicol regimens, but the shorter standard regimen still achieved microbiological cure and reduces the risk of negative sequelae associated with treatment and/or captivity and treatment costs. Despite these positive clinical outcomes, alternatives to chloramphenicol are warranted due to its decreasing availability.

Chlamydia pecorum gastrointestinal tract infection associations with urogenital tract infections in the koala (Phascolarctos cinereus)

Background

Chlamydia infects multiple sites within hosts, including the gastrointestinal tract (GIT). In certain hosts, gastrointestinal infection is linked to treatment avoidance and self-infection at disease susceptible sites. GIT C. pecorum has been detected in livestock and koalas, however GIT prevalence rates within the koala are yet to be established.

Methods

Paired conjunctival, urogenital and rectal samples from 33 koalas were screened for C. pecorum and C. pecorum plasmid using 16S rRNA and CDS5-specific quantitative PCR assays, respectively. Amplicon sequencing of 359 bp ompA fragment was used to identify site-specific genotypes.

Results

The overall C. pecorum prevalence collectively (healthy and clinically diseased koalas) was 51.5%, 57.6% and 42.4% in urogenital, conjunctival and gastrointestinal sites, respectively. Concurrent urogenital and rectal Chlamydia was identified in 14 koalas, with no cases of GIT only Chlamydia shedding. The ompA genotype G dominated the GIT positive samples, and genotypes A and E’ were dominant in urogenital tract (UGT) positive samples. Increases in C. pecorum plasmid per C. pecorum load (detected by PCR) showed clustering in the clinically diseased koala group (as assessed by scatter plot analysis). There was also a low correlation between plasmid positivity and C. pecorum infected animals at any site, with a prevalence of 47% UGT, 36% rectum and 40% faecal pellet.

Conclusions

GIT C. pecorum PCR positivity suggests that koala GIT C. pecorum infections are common and occur regularly in animals with concurrent genital tract infections. GIT dominant genotypes were identified and do not appear to be related to plasmid positivity. Preliminary results indicated a possible association between C. pecorum plasmid load and clinical UGT disease.

Extracellular HtrA serine proteases: An emerging new strategy in bacterial pathogenesis

The HtrA family of chaperones and serine proteases is important for regulating stress responses and controlling protein quality in the periplasm of bacteria. HtrA is also associated with infectious diseases since inactivation of htrA genes results in significantly reduced virulence properties by various bacterial pathogens. These virulence features of HtrA can be attributed to reduced fitness of the bacteria, higher susceptibility to environmental stress and/or diminished secretion of virulence factors. In some Gram-negative and Gram-positive pathogens, HtrA itself can be exposed to the extracellular environment promoting bacterial colonisation and invasion of host tissues. Most of our knowledge on the function of exported HtrAs stems from research on Helicobacter pylori, Campylobacter jejuni, Borrelia burgdorferi, Bacillus anthracis, and Chlamydia species. Here, we discuss recent progress showing that extracellular HtrAs are able to cleave cell-to-cell junction factors including E-cadherin, occludin, and claudin-8, as well as extracellular matrix proteins such as fibronectin, aggrecan, and proteoglycans, disrupting the epithelial barrier and producing substantial host cell damage. We propose that the export of HtrAs is a newly discovered strategy, also applied by additional bacterial pathogens. Consequently, exported HtrA proteases represent highly attractive targets for antibacterial treatment by inhibiting their proteolytic activity or application in vaccine development.

Peptide selectivity between the PDZ domains of human pregnancy-related serine proteases (HtrA1, HtrA2, HtrA3, and HtrA4) can be reshaped by different halogen probes

The human HtrA family of serine proteases (HtrA1, HtrA2, HtrA3, and HtrA4) are the key enzymes associated with pregnancy and closely related to the development and progression of many pathological events. Previously, it was found that halogen substitution at the indole moiety of peptide Trp-1 residue can form a geometrically satisfactory halogen bond with the Drosophila discs large, zona occludens-1 (PDZ) domain of HtrA proteases. Here, we attempt to systematically investigate the effect of substitution with 4 halogen types and 2 indole positions on the binding affinity and specificity of peptide ligands to the 4 HtrA PDZ domains. The complex structures, interaction energies, halogen-bonding strength, and binding affinity of domain-peptide systems were modeled, analyzed, and measured via computational modeling and fluorescence-based assay. It is revealed that there is a compromise between the local rearrangement of halogen bond involving different halogen atoms and the global optimization of domain-peptide interaction; the substitution position is fundamentally important for peptide-binding affinity, while the halogen type can effectively shift peptide selectivity between the 4 domains. The HtrA1-PDZ and HtrA4-PDZ as well as HtrA2-PDZ and HtrA3-PDZ respond similarly to different halogen substitutions of peptide; -Br substitution at R2-position and -I substitution at R4-position are most effective in improving peptide selectivity for HtrA1-PDZ/HtrA4-PDZ and HtrA2-PDZ/HtrA3-PDZ, respectively; -F substitution would not address substantial effect on peptide selectivity for all the 4 domains. Consequently, the binding affinities of a native peptide ligand DSRIWWV-COOH as well as its 4 R2-halogenated counterparts were determined as 1.9, 1.4, 0.5, 0.27, and 0.92 μM, which are basically consistent with computational analysis. This study would help to rationally design selective peptide inhibitors of HtrA family members by using different halogen substitutions.

Copper(II)-bis(thiosemicarbazonato) complexes as anti-chlamydial agents

Lipophilic copper (Cu)-containing complexes have shown promising antibacterial activity against a range of bacterial pathogens. To examine the susceptibility of the intracellular human pathogen Chlamydia trachomatis to copper complexes containing bis(thiosemicarbazone) ligands [Cu(btsc)], we tested the in vitro effect of CuII-diacetyl- and CuII-glyoxal-bis[N(4)-methylthiosemicarbazonato] (Cu(atsm) and Cu(gtsm), respectively) on C. trachomatis. Cu(atsm) and to a greater extent, Cu(gtsm), prevented the formation of infectious chlamydial progeny. Impacts on host cell viability and respiration were also observed in addition to the Chlamydia impacts. This work suggests that copper-based complexes may represent a new lead approach for future development of new therapeutics against chlamydial infections, although host cell impacts need to be fully explored.

Characterization of shifts of koala (Phascolarctos cinereus) intestinal microbial communities associated with antibiotic treatment

Koalas (Phascolarctos cinereus) are arboreal marsupials native to Australia that eat a specialized diet of almost exclusively eucalyptus leaves. Microbes in koala intestines are known to break down otherwise toxic compounds, such as tannins, in eucalyptus leaves. Infections by Chlamydia, obligate intracellular bacterial pathogens, are highly prevalent in koala populations. If animals with Chlamydia infections are received by wildlife hospitals, a range of antibiotics can be used to treat them. However, previous studies suggested that koalas can suffer adverse side effects during antibiotic treatment. This study aimed to use 16S rRNA gene sequences derived from koala feces to characterize the intestinal microbiome of koalas throughout antibiotic treatment and identify specific taxa associated with koala health after treatment. Although differences in the alpha diversity were observed in the intestinal flora between treated and untreated koalas and between koalas treated with different antibiotics, these differences were not statistically significant. The alpha diversity of microbial communities from koalas that lived through antibiotic treatment versus those who did not was significantly greater, however. Beta diversity analysis largely confirmed the latter observation, revealing that the overall communities were different between koalas on antibiotics that died versus those that survived or never received antibiotics. Using both machine learning and OTU (operational taxonomic unit) co-occurrence network analyses, we found that OTUs that are very closely related to Lonepinella koalarum, a known tannin degrader found by culture-based methods to be present in koala intestines, was correlated with a koala’s health status. This is the first study to characterize the time course of effects of antibiotics on koala intestinal microbiomes. Our results suggest it may be useful to pursue alternative treatments for Chlamydia infections without the use of antibiotics or the development of Chlamydia-specific antimicrobial compounds that do not broadly affect microbial communities.

CtHtrA: the lynchpin of the chlamydial surface and a promising therapeutic target

Chlamydia trachomatis is the most prevalent sexually transmitted bacterial infection worldwide and the leading cause of preventable blindness. Reports have emerged of treatment failure, suggesting a need to develop new antibiotics to battle Chlamydia infection. One possible candidate for a new treatment is the protease inhibitor JO146, which is an effective anti-Chlamydia agent that targets the CtHtrA protein. CtHtrA is a lynchpin on the chlamydial cell surface due to its essential and multifunctional roles in the bacteria's stress response, replicative phase of development, virulence and outer-membrane protein assembly. This review summarizes the current understanding of CtHtrA function and presents a mechanistic model that highlights CtHtrA as an effective target for anti-Chlamydia drug development.