Genome sequencing of recent clinical Chlamydia trachomatis strains identifies loci associated with tissue tropism and regions of apparent recombination

Genomic insights into local-scale evolution of ocular Chlamydia trachomatis strains within and between individuals in Gambian trachoma-endemic villages

Trachoma, a neglected tropical disease caused by Chlamydia trachomatis (Ct) serovars A-C, is the leading infectious cause of blindness worldwide. Africa bears the highest burden, accounting for over 86 % of global trachoma cases. We investigated Ct serovar A (SvA) and B (SvB) whole genome sequences prior to the induction of mass antibiotic drug administration in The Gambia. Here, we explore the factors contributing to Ct strain diversification and the implications for Ct evolution within the context of ocular infection. A cohort study in 2002-2003 collected ocular swabs across nine Gambian villages during a 6 month follow-up study. To explore the genetic diversity of Ct within and between individuals, we conducted whole-genome sequencing (WGS) on a limited number (n=43) of Ct-positive samples with an omcB load ≥10 from four villages. WGS was performed using target enrichment with SureSelect and Illumina paired-end sequencing. Out of 43 WGS samples, 41 provided sufficient quality for further analysis. ompA analysis revealed that 11 samples had highest identity to ompA from strain A/HAR13 (NC_007429) and 30 had highest identity to ompA from strain B/Jali20 (NC_012686). While SvB genome sequences formed two distinct village-driven subclades, the heterogeneity of SvA sequences led to the formation of many individual branches within the Gambian SvA subclade. Comparing the Gambian SvA and SvB sequences with their reference strains, Ct A/HAR13 and Ct B/Jali20, indicated an single nucleotide polymorphism accumulation rate of 2.4×10-5 per site per year for the Gambian SvA and 1.3×10-5 per site per year for SvB variants (P<0.0001). Variant calling resulted in a total of 1371 single nucleotide variants (SNVs) with a frequency >25 % in SvA sequences, and 438 SNVs in SvB sequences. Of note, in SvA variants, highest evolutionary pressure was recorded on genes responsible for host cell modulation and intracellular survival mechanisms, whereas in SvB variants this pressure was mainly on genes essential for DNA replication/repair mechanisms and protein synthesis. A comparison of the sequences between observed separate infection events (4-20 weeks between infections) suggested that the majority of the variations accumulated in genes responsible for host-pathogen interaction such as CTA_0166 (phospholipase D-like protein), CTA_0498 (TarP) and CTA_0948 (deubiquitinase). This comparison of Ct SvA and SvB variants within a trachoma endemic population focused on their local evolutionary adaptation. We found a different variation accumulation pattern in the Gambian SvA chromosomal genes compared with SvB, hinting at the potential of Ct serovar-specific variation in diversification and evolutionary fitness. These findings may have implications for optimizing trachoma control and prevention strategies.

Recent advances in genetic systems in obligate intracellular human-pathogenic bacteria

The ability to genetically manipulate a pathogen is fundamental to discovering factors governing host-pathogen interactions at the molecular level and is critical for devising treatment and prevention strategies. While the genetic "toolbox" for many important bacterial pathogens is extensive, approaches for modifying obligate intracellular bacterial pathogens were classically limited due in part to the uniqueness of their obligatory lifestyles. Many researchers have confronted these challenges over the past two and a half decades leading to the development of multiple approaches to construct plasmid-bearing recombinant strains and chromosomal gene inactivation and deletion mutants, along with gene-silencing methods enabling the study of essential genes. This review will highlight seminal genetic achievements and recent developments (past 5 years) for Anaplasma spp., Rickettsia spp., Chlamydia spp., and Coxiella burnetii including progress being made for the still intractable Orientia tsutsugamushi. Alongside commentary of the strengths and weaknesses of the various approaches, future research directions will be discussed to include methods for C. burnetii that should have utility in the other obligate intracellular bacteria. Collectively, the future appears bright for unraveling the molecular pathogenic mechanisms of these significant pathogens.

Genetic Characterization of Non-Lymphogranuloma venereum Chlamydia trachomatis Indicates Distinct Infection Transmission Networks in Spain

Chlamydia trachomatis infection is an important public health problem. Our objective was to assess the dynamics of the transmission of this infection, analysing the distribution of circulating ompA genotypes and multilocus sequence types of C. trachomatis in Spain as a function of clinical and epidemiological variables. During 2018 and 2019, we genetically characterized C. trachomatis in tertiary hospitals in six areas in Spain (Asturias, Barcelona, Gipuzkoa, Mallorca, Seville and Zaragoza), with a catchment population of 3.050 million people. Genotypes and sequence types were obtained using polymerase chain reaction techniques that amplify a fragment of the ompA gene, and five highly variable genes (hctB, CT058, CT144, CT172 and pbpB), respectively. Amplicons were sequenced and phylogenetic analysis was conducted. We obtained genotypes in 636/698 cases (91.1%). Overall and by area, genotype E was the most common (35%). Stratifying by sex, genotypes D and G were more common among men, and genotypes F and I among women (p < 0.05). Genotypes D, G and J were more common in men who have sex with men (MSM) than in men who have sex with women (MSW), in whom the most common genotypes were E and F. The diversity index was higher in sequence typing (0.981) than in genotyping (0.791), and the most common sequence types were ST52 and ST108 in MSM, and ST30, ST148, ST276 and ST327 in MSW. Differences in genotype distribution between geographical areas were attributable to differences in population characteristics. The transmission dynamics varied with sexual behaviour: the predominant genotypes and most frequent sequence types found in MSM were different to those detected in MSW and women.

Patterns of within-host spread of Chlamydia trachomatis between vagina, endocervix and rectum revealed by comparative genomic analysis

Introduction

Chlamydia trachomatis, a gram-negative obligate intracellular bacterium, commonly causes sexually transmitted infections (STIs). Little is known about C. trachomatis transmission within the host, which is important for understanding disease epidemiology and progression.

Methods

We used RNA-bait enrichment and whole-genome sequencing to compare rectal, vaginal and endocervical samples collected at the same time from 26 study participants who attended Fijian Ministry of Health and Medical Services clinics and tested positive for C. trachomatis at each anatomic site.

Results

The 78 C. trachomatis genomes from participants resolved into two major clades of the C. trachomatis phylogeny (the "prevalent urogenital and anorectal" clade and "non-prevalent urogenital and anorectal" clade). For 21 participants, genome sequences were almost identical in each anatomic site. For the other five participants, two distinct C. trachomatis strains were present in different sites; in two cases, the vaginal sample was a mixture of strains.

Discussion

The absence of large numbers of fixed SNPs between C. trachomatis genomes within many of the participants could indicate recent acquisition of infection prior to the clinic visit without sufficient time to accumulate significant genetic variation in different body sites. This model suggests that many C. trachomatis infections may be resolved relatively quickly in the Fijian population, possibly reflecting common prescription or over-the-counter antibiotics usage.

Patterns of within-host spread of Chlamydia trachomatis between vagina, endocervix and rectum revealed by comparative genomic analysis

Chlamydia trachomatis , a gram-negative obligate intracellular bacterium, commonly causes sexually transmitted infections (STIs). Little is known about C. trachomatis transmission within the host, which is important for understanding disease epidemiology and progression. We used RNA-bait enrichment and whole-genome sequencing to compare rectal, vaginal and endocervical samples collected at the same time from 26 study participants who attended Fijian Ministry of Health and Medical Services clinics and tested positive for C. trachomatis at each anatomic site. The 78 C. trachomatis genomes from participants were from two major clades of the C. trachomatis phylogeny (the "prevalent urogenital and anorecta"l clade and "non-prevalent urogenital and anorectal" clade). For 21 participants, genome sequences were almost identical in each anatomic site. For the other five participants, two distinct C. trachomatis strains were present in different sites; in two cases, the vaginal sample was a mixture of strains. The absence of large numbers of fixed SNPs between C. trachomatis strains within many of the participants could indicate recent acquisition of infection prior to the clinic visit without sufficient time to accumulate significant variation in the different body sites. This model suggests that many C. trachomatis infections may be resolved relatively quickly in the Fijian population, possibly reflecting common prescription or over-the-counter antibiotics usage.

Importance

Chlamydia trachomatis is a bacterial pathogen that causes millions of sexually transmitted infections (STIs) annually across the globe. Because C. trachomatis lives inside human cells, it has historically been hard to study. We know little about how the bacterium spreads between body sites. Here, samples from 26 study participants who had simultaneous infections in their vagina, rectum and endocervix were genetically analyzed using an improved method to extract C. trachomatis DNA directly from clinical samples for genome sequencing. By analyzing patterns of mutations in the genomes, we found that 21 participants shared very similar C. trachomatis strains in all three anatomic sites, suggesting recent infection and spread. For five participants two C. trachomatis strains were evident, indicating multiple infections. This study is significant in that improved enrichment methods for genome sequencing provides robust data to genetically trace patterns of C. trachomatis infection and transmission within an individual for epidemiologic and pathogenesis interrogations.

Genomic Analysis of MSM Rectal Chlamydia trachomatis Isolates Identifies Predicted Tissue-Tropic Lineages Generated by Intraspecies Lateral Gene Transfer-Mediated Evolution

Chlamydia trachomatis is an obligate intracellular bacterium that causes serious diseases in humans. Rectal infection and disease caused by this pathogen are important yet understudied aspects of C. trachomatis natural history. The University of Washington Chlamydia Repository has a large collection of male-rectal-sourced strains (MSM rectal strains) isolated in Seattle, USA and Lima, Peru. Initial characterization of strains collected over 30 years in both Seattle and Lima led to an association of serovars G and J with male rectal infections. Serovar D, E, and F strains were also collected from MSM patients. Genome sequence analysis of a subset of MSM rectal strains identified a clade of serovar G and J strains that had high overall genomic identity. A genome-wide association study was then used to identify genomic loci that were correlated with tissue tropism in a collection of serovar-matched male rectal and female cervical strains. The polymorphic membrane protein PmpE had the strongest correlation, and amino acid sequence alignments identified a set of PmpE variable regions (VRs) that were correlated with host or tissue tropism. Examination of the positions of VRs by the protein structure-predicting Alphafold2 algorithm demonstrated that the VRs were often present in predicted surface-exposed loops in both PmpE and PmpH protein structure. Collectively, these studies identify possible tropism-predictive loci for MSM rectal C. trachomatis infections and identify predicted surface-exposed variable regions of Pmp proteins that may function in MSM rectal versus cervical tropism differences.

A Review of Next Generation Sequencing Methods and its Applications in Laboratory Diagnosis

Next-generation sequencing (NGS) is a new technology used to detect the sequence of DNA and RNA and to detect mutations or variations of significance. NGS generates large quantities of sequence data within a short time duration. The various types of sequencing includes Sanger Sequencing, Pyrosequencing, Sequencing by Synthesis (Illumina), Ligation (SoLID), Single molecule Fluorescent Sequencing (Helicos), Single molecule Real time Sequencing (Pacbio), Semiconductor sequencing (Ion torrent technology), Nanopore sequencing and fourth generation sequencing. These methods of sequencing have been modified and improved over the years such that it has become cost effective and accessible to diagnostic laboratories. Management of Outbreaks, rapid identification of bacteria, molecular case finding, taxonomy, detection of the zoonotic agents and guiding prevention strategies in HIV outbreaks are just a few of the many applications of Next Generation sequencing in clinical microbiology.

The Impact of Lateral Gene Transfer in Chlamydia

Lateral gene transfer (LGT) facilitates many processes in bacterial ecology and pathogenesis, especially regarding pathogen evolution and the spread of antibiotic resistance across species. The obligate intracellular chlamydiae, which cause a range of diseases in humans and animals, were historically thought to be highly deficient in this process. However, research over the past few decades has demonstrated that this was not the case. The first reports of homologous recombination in the Chlamydiaceae family were published in the early 1990s. Later, the advent of whole-genome sequencing uncovered clear evidence for LGT in the evolution of the Chlamydiaceae, although the acquisition of tetracycline resistance in Chlamydia (C.) suis is the only recent instance of interphylum LGT. In contrast, genome and in vitro studies have shown that intraspecies DNA exchange occurs frequently and can even cross species barriers between closely related chlamydiae, such as between C. trachomatis, C. muridarum, and C. suis. Additionally, whole-genome analysis led to the identification of various DNA repair and recombination systems in C. trachomatis, but the exact machinery of DNA uptake and homologous recombination in the chlamydiae has yet to be fully elucidated. Here, we reviewed the current state of knowledge concerning LGT in Chlamydia by focusing on the effect of homologous recombination on the chlamydial genome, the recombination machinery, and its potential as a genetic tool for Chlamydia.

A broad-spectrum cloning vector that exists as both an integrated element and a free plasmid in Chlamydia trachomatis

Plasmid transformation of chlamydiae has created new opportunities to investigate host-microbe interactions during chlamydial infections; however, there are still limitations. Plasmid transformation requires a replicon derived from the native Chlamydia plasmid, and these transformations are species-specific. We explored the utility of a broad host-range plasmid, pBBR1MCS-4, to transform chlamydiae, with a goal of simplifying the transformation process. The plasmid was modified to contain chromosomal DNA from C. trachomatis to facilitate homologous recombination. Sequences flanking incA were cloned into the pBBR1MCS-4 vector along with the GFP:CAT cassette from the pSW2-GFP chlamydial shuttle vector. The final plasmid construct, pBVR2, was successfully transformed into C. trachomatis strain L2-434. Chlamydial transformants were analyzed by immunofluorescence microscopy and positive clones were sequentially purified using limiting dilution. PCR and PacBio-based whole genome sequencing were used to determine if the plasmid was maintained within the chromosome or as an episome. PacBio sequencing of the cloned transformants revealed allelic exchange events between the chromosome and plasmid pBVR2 that replaced chromosomal incA with the plasmid GFP:CAT cassette. The data also showed evidence of full integration of the plasmid into the bacterial chromosome. While some plasmids were fully integrated, some were maintained as episomes and could be purified and retransformed into E. coli. Thus, the plasmid can be successfully transformed into chlamydia without a chlamydial origin of replication and can exist in multiple states within a transformed population.

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.

Spread of clonal genovar E Chlamydia trachomatis among men who have sex with men

In a previous study, we developed a Multi-Locus VNTRs Analysis (MLVA) typing system, called MLVA-5, for the discrimination of Chlamydia trachomatis genovar E strain. The results suggested the clonal spread of a MLVA-5 type 21 strain among men who have sex with men (MSM). We applied the MLVA-5 typing method on 157 French anorectal genovar E specimens and 19 Swedish specimens collected between 2010 and 2015. A total of 29 MLVA-5 types was obtained, with three predominant types among French samples: 78 specimens belonged to MLVA-5 type 21, two other types, 11 and 13, included 9 and 14 specimens, respectively. In 15 cases, one unique MLVA-5 type was observed for a single patient, 7 of which were new types not previously described. The distribution of MLVA-5 types according to sexual orientation showed that the 7 anorectal specimens from heterosexual patients belonged to 6 genotypes, and the 12 anorectal specimens from bisexual patients comprised eight types. The 95 anorectal specimens from MSM were distributed into 22 types, but 55 (57.9%) of them belonged to MLVA-5 type 21. Among the Swedish specimens from MSM, eight were from MLVA-type 21 (4 urines and 4 anorectal specimens). The results support the hypothesis of the spread of clonal genovar E strain among MSM.

High-resolution genotyping of Lymphogranuloma Venereum (LGV) strains of Chlamydia trachomatis in London using multi-locus VNTR analysis-ompA genotyping (MLVA-ompA)

BACKGROUND

Lymphogranuloma venereum (LGV) is caused by Chlamydia trachomatis strains with ompA genotypes L1 to L3. An LGV epidemic associated with the L2b genotype has emerged in the past few decades amongst men who have sex with men (MSM). C. trachomatis genotypes can be discriminated by outer membrane protein A gene (ompA) sequencing, however this method has limited resolution. This study employed a high-resolution genotyping method, namely, multi-locus tandem repeat (VNTR) analysis with ompA sequencing (MLVA-ompA), to assess the distribution of LGV MLVA-ompA genotypes amongst individuals attending genitourinary medicine (GUM) clinics in London.

METHODS

Clinical specimens were collected from individuals attending eight London-based GUM clinics. Specimens that tested positive for C. trachomatis by commercial nucleic acid amplification test (NAAT) were confirmed as LGV by pmpH real-time PCR. LGV-positive DNA extracts were subsequently genotyped using MLVA-ompA.

RESULTS

Two hundred and thirty DNA extracts were confirmed as LGV, and 162 (70%) yielded complete MLVA-ompA genotypes. Six LGV MLVA-ompA genotypes were identified: 1.9.2b-L2, 1.9.3b-L2b, 1.9.2b-L2b, 1.9.2b-L2b/D, 1.4a.2b-L2b, and 5.9.2b-L1. The following LGV ompA genotypes were identified (in descending order of abundance): L2, L2b, L2b/D, and L1. Eight ompA sequences with the hybrid L2b/D profile were detected. The hybrid sequence was identical to the ompA of a recombinant L2b/D strain detected in Portugal in 2017.

CONCLUSIONS

The L2 ompA genotype was found to predominate in the London study population. The study detected an unusual hybrid L2b/D ompA profile that was previously reported in Portugal. We recommend further monitoring and surveillance of LGV strains within the UK population.

Tryptophan Operon Diversity Reveals Evolutionary Trends among Geographically Disparate Chlamydia trachomatis Ocular and Urogenital Strains Affecting Tryptophan Repressor and Synthase Function

The obligate intracellular pathogen Chlamydia trachomatis (Ct) is the leading cause of bacterial sexually transmitted infections and blindness globally. To date, Ct urogenital strains are considered tryptophan prototrophs, utilizing indole for tryptophan synthesis within a closed-conformation tetramer comprised of two α (TrpA)- and two β (TrpB)-subunits. In contrast, ocular strains are auxotrophs due to mutations in TrpA, relying on host tryptophan pools for survival. It has been speculated that there is strong selective pressure for urogenital strains to maintain a functional operon. Here, we performed genetic, phylogenetic, and novel functional modeling analyses of 595 geographically diverse Ct ocular, urethral, vaginal, and rectal strains with complete operon sequences. We found that ocular and urogenital, but not lymphogranuloma venereum, TrpA-coding sequences were under positive selection. However, vaginal and urethral strains exhibited greater nucleotide diversity and a higher ratio of nonsynonymous to synonymous substitutions [Pi(a)/Pi(s)] than ocular strains, suggesting a more rapid evolution of beneficial mutations. We also identified nonsynonymous amino acid changes for an ocular isolate with a urogenital backbone in the intergenic region between TrpR and TrpB at the exact binding site for YtgR-the only known iron-dependent transcription factor in Chlamydia-indicating that selective pressure has disabled the response to fluctuating iron levels. In silico effects on protein stability, ligand-binding affinity, and tryptophan repressor (TrpR) affinity for single-stranded DNA (ssDNA) measured by calculating free energy changes (ΔΔG) between Ct reference and mutant tryptophan operon proteins were also analyzed. We found that tryptophan synthase function was likely suboptimal compared to other bacterial tryptophan prototrophs and that a diversity of urogenital strain mutations rendered the synthase nonfunctional or inefficient. The novel mutations identified here affected active sites in an orthosteric manner but also hindered α- and β-subunit allosteric interactions from distant sites, reducing efficiency of the tryptophan synthase. Importantly, strains with mutant proteins were inclined toward energy conservation by exhibiting an altered affinity for their respective ligands compared to reference strains, indicating greater fitness. This is not surprising as l-tryptophan is one of the most energetically costly amino acids to synthesize. Mutations in the tryptophan repressor gene (trpR) among urogenital strains were similarly detrimental to function. Our findings indicate that urogenital strains are evolving more rapidly than previously recognized with mutations that impact tryptophan operon function in a manner that is energetically beneficial, providing a novel host-pathogen evolutionary mechanism for intracellular survival.IMPORTANCE Chlamydia trachomatis (Ct) is a major global public health concern causing sexually transmitted and ocular infections affecting over 130 million and 260 million people, respectively. Sequelae include infertility, preterm birth, ectopic pregnancy, and blindness. Ct relies on available host tryptophan pools and/or substrates to synthesize tryptophan to survive. Urogenital strains synthesize tryptophan from indole using their intact tryptophan synthase (TS). Ocular strains contain a trpA frameshift mutation that encodes a truncated TrpA with loss of TS function. We found that TS function is likely suboptimal compared to other tryptophan prototrophs and that urogenital stains contain diverse mutations that render TS nonfunctional/inefficient, evolve more rapidly than previously recognized, and impact operon function in a manner that is energetically beneficial, providing an alternative host-pathogen evolutionary mechanism for intracellular survival. Our research has broad scientific appeal since our approach can be applied to other bacteria that may explain evolution/survival in host-pathogen interactions.

A Genital Infection-Attenuated Chlamydia muridarum Mutant Infects the Gastrointestinal Tract and Protects against Genital Tract Challenge

Chlamydia spp. productively infect mucosal epithelial cells of multiple anatomical sites, including the conjunctiva, lungs, gastrointestinal (GI) tract, and urogenital tract. We, and others, previously established that chlamydial GI tropism is mediated by distinct chromosomal and plasmid factors. In this study, we describe a genital infection-attenuated Chlamydia muridarum mutant (GIAM-1) that is profoundly and specifically attenuated in the murine genital tract. GIAM-1 infected the murine GI tract similarly to wild-type (WT) Chlamydia muridarum but did not productively infect the lower genital tract of female mice, ascend to infect the upper genital tract, or cause hydrosalpinx. However, GI infection of mice with GIAM-1 elicited a transmucosal immune response that protected against subsequent genital challenge with WT Chlamydia muridarum Collectively, our results demonstrate that chlamydia mutants that are profoundly attenuated for specific organ tissues can be derived and demonstrate that live-attenuated vaccine strains that infect the GI tract, but do not elicit genital tract disease, could be used to protect against chlamydia genital tract infection and disease.IMPORTANCE Chlamydia is the most common sexually transmitted bacterial infection in the United States. Most chlamydia genital infections resolve without serious consequences; however, untreated infection in women can cause pelvic inflammatory disease and infertility. Antibiotics are very effective in treating chlamydia, but most genital infections in both men and women are asymptomatic and go undiagnosed. Therefore, there is a critical need for an effective vaccine. In this work, we show that a mutant chlamydia strain, having substantially reduced virulence for genital infection, colonizes the gastrointestinal tract and produces robust immunity to genital challenge with fully virulent wild-type chlamydia. These results are an important advance in understanding chlamydial virulence and provide compelling evidence that safe and effective live-attenuated chlamydia vaccines may be feasible.

Spectroscopic analysis of chlamydial major outer membrane protein in support of structure elucidation

Chlamydial major outer membrane protein (MOMP) is the major protein constituent of the bacterial pathogen Chlamydia trachomatis. Chlamydia trachomatis Serovars D–K are the leading cause of genital tract infections which can lead to infertility or ectopic pregnancies. A vaccine against Chlamydia is highly desirable but currently not available. MOMP accounts for ~ 60% of the chlamydial protein mass and is considered to be one of the lead vaccine candidates against C. trachomatis. We report on the spectroscopic analysis of C. trachomatis native MOMP Serovars D, E, F, and J as well as C. muridarum MOMP by size exclusion chromatography multi angle light scattering (SEC MALS), circular dichroism (CD) and attenuated total reflectance Fourier transform infrared spectroscopy (ATR‐FTIR). MOMP was purified from the native bacterium grown in either adherent HeLa cells or in different suspension cell lines. Our results confirm that MOMP forms homo‐trimers in detergent micelles. The secondary structure composition of C. trachomatis MOMP was conserved across serovars, but different from composition of C. muridarum MOMP with a 13% (CD) to 18% (ATR‐FTIR) reduction in β‐sheet conformation for C. trachomatis MOMP. When Serovar E MOMP was isolated from suspension cell lines the α‐helix content increased by 7% (CD) to 13% (ATIR‐FTIR). Maintenance of a native‐like tertiary and quaternary structure in subunit vaccines is important for the generation of protective antibodies. This biophysical characterization of MOMP presented here serves, in the absence of functional assays, as a method for monitoring the structural integrity of MOMP.

Chromosomal Recombination Targets in Chlamydia Interspecies Lateral Gene Transfer

Lateral gene transfer (LGT) among Chlamydia trachomatis strains is common, in both isolates generated in the laboratory and those examined directly from patients. In contrast, there are very few examples of recent acquisition of DNA by any Chlamydia spp. from any other species. Interspecies LGT in this system was analyzed using crosses of tetracycline (Tc)-resistant C. trachomatis L2/434 and chloramphenicol (Cam)-resistant C. muridarum VR-123. Parental C. muridarum strains were created using a plasmid-based Himar transposition system, which led to integration of the Cam^r marker randomly across the chromosome. Fragments encompassing 79% of the C. muridarum chromosome were introduced into a C. trachomatis background, with the total coverage contained on 142 independent recombinant clones. Genome sequence analysis of progeny strains identified candidate recombination hot spots, a property not consistent with in vitro C. trachomatis × C. trachomatis (intraspecies) crosses. In both interspecies and intraspecies crosses, there were examples of duplications, mosaic recombination endpoints, and recombined sequences that were not linked to the selection marker. Quantitative analysis of the distribution and constitution of inserted sequences indicated that there are different constraints on interspecies LGT than on intraspecies crosses. These constraints may help explain why there is so little evidence of interspecies genetic exchange in this system, which is in contrast to very widespread intraspecies exchange in C. trachomatis IMPORTANCE Genome sequence analysis has demonstrated that there is widespread lateral gene transfer among strains within the species C. trachomatis and with other closely related Chlamydia species in laboratory experiments. This is in contrast to the complete absence of foreign DNA in the genomes of sequenced clinical C. trachomatis strains. There is no understanding of any mechanisms of genetic transfer in this important group of pathogens. In this report, we demonstrate that interspecies genetic exchange can occur but that the nature of the fragments exchanged is different than those observed in intraspecies crosses. We also generated a large hybrid strain library that can be exploited to examine important aspects of chlamydial disease.

Whole-genome sequencing of ocular Chlamydia trachomatis isolates from Gadarif State, Sudan

BACKGROUND

Trachoma, caused by ocular Chlamydia trachomatis, is the leading infectious cause of blindness worldwide. Sudan first reported trachoma in the 1930s and has since been consistently endemic. Ocular C. trachomatis previously isolated from trachoma patients in Sudan in 1963 was antigenically identical to an isolate from Saudi Arabia (A/SA1). No contemporary ocular C. trachomatis whole genome sequences have been reported from Sudan.

METHODS

This study sequenced twenty ocular C. trachomatis isolates to improve understanding of pathogen diversity in North-East Africa and examine for genomic variation specific to Sudan, possibly related to the persistence of trachoma in surveyed communities. High quality, whole genome sequences were obtained from 12/20 isolates.

RESULTS

All isolates were serovar A and had tarP and trpA sequences typical of classical, ocular C. trachomatis isolates. The Sudanese isolates formed a closely related subclade within the T2-trachoma clade of C. trachomatis phylogeny distinct from geographically disparate ocular isolates, with little intra-population diversity. We found 333 SNPs that were conserved in Sudanese ocular isolates but rare compared to other ocular C. trachomatis populations, which were focused in two genomic loci (CTA0172-CTA0173 and CTA0482).

CONCLUSIONS

Limited intra-population diversity and geographical clustering of ocular C. trachomatis suggests minimal transmission between and slow diversification within trachoma-endemic communities. However, diversity may have been higher pre-treatment in these communities. Over-representation of Sudan-specific SNPs in three genes suggests they may have an impact on C. trachomatis growth and transmission in this population.

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.

Transposon Mutagenesis in Chlamydia trachomatis Identifies CT339 as a ComEC Homolog Important for DNA Uptake and Lateral Gene Transfer

Transposon mutagenesis is a widely applied and powerful genetic tool for the discovery of genes associated with selected phenotypes. Chlamydia trachomatis is a clinically significant, obligate intracellular bacterium for which many conventional genetic tools and capabilities have been developed only recently. This report describes the successful development and application of a Himar transposon mutagenesis system for generating single-insertion mutant clones of C. trachomatis This system was used to generate a pool of 105 transposon mutant clones that included insertions in genes encoding flavin adenine dinucleotide (FAD)-dependent monooxygenase (C. trachomatis 148 [ct148]), deubiquitinase (ct868), and competence-associated (ct339) proteins. A subset of Tn mutant clones was evaluated for growth differences under cell culture conditions, revealing that most phenocopied the parental strain; however, some strains displayed subtle and yet significant differences in infectious progeny production and inclusion sizes. Bacterial burden studies in mice also supported the idea that a FAD-dependent monooxygenase (ct148) and a deubiquitinase (ct868) were important for these infections. The ct339 gene encodes a hypothetical protein with limited sequence similarity to the DNA-uptake protein ComEC. A transposon insertion in ct339 rendered the mutant incapable of DNA acquisition during recombination experiments. This observation, along with in situ structural analysis, supports the idea that this protein is playing a role in the fundamental process of lateral gene transfer similar to that of ComEC. In all, the development of the Himar transposon system for Chlamydia provides an effective genetic tool for further discovery of genes that are important for basic biology and pathogenesis aspects.IMPORTANCE Chlamydia trachomatis infections have an immense impact on public health; however, understanding the basic biology and pathogenesis of this organism has been stalled by the limited repertoire of genetic tools. This report describes the successful adaptation of an important tool that has been lacking in Chlamydia studies: transposon mutagenesis. This advance enabled the generation of 105 insertional mutants, demonstrating that numerous gene products are not essential for in vitro growth. Mammalian infections using these mutants revealed that several gene products are important for infections in vivo Moreover, this tool enabled the investigation and discovery of a gene critical for lateral gene transfer; a process fundamental to the evolution of bacteria and likely for Chlamydia as well. The development of transposon mutagenesis for Chlamydia has broad impact for the field and for the discovery of genes associated with selected phenotypes, providing an additional avenue for the discovery of molecular mechanisms used for pathogenesis and for a more thorough understanding of this important pathogen.

An Asymptomatic Patient with Fatal Infertility Carried a Swedish Strain of Chlamydia trachomatis with Additional Deletion in The Plasmid orf1 that Belonged to A Different MLST Sequence Type

Here, we present the first case of asymptomatic genital Chlamydial infection caused by the new emerging Chlamydia trachomatis (C.t.) ST13 strain genovar E, which has a double deletion of 377 bp and 17 bp in orf1 gene of the cryptic plasmid (ddCT). This case occurred in an infertile patient (case-patient) with a detectable level of Chlamydial antibodies and a spermatozoa deficiency known as azoospermia. Additionally, the ddCT strain showed the presence of a duplication of 44 bp in the plasmid orf3 and SNP in orf4, which were known as the typical characteristics of the Swedish variant of C.t. (nvCT) genovar E. Multilocus sequence typing (MLST) determined a significant difference between ddCT and nvCT in four alleles (oppA, hfiX, gitA and enoA). Both ddCT and nvCT were assigned to different genetic lineages and could be allocated to two different non-overlapping clonal complexes. Furthermore, ddCT demonstrated a considerable difference among 4–5 alleles in comparison with other C.t. strains of genovar E of ST4, ST8, ST12, and ST94, including the founder of a single relevant cluster, wtCT E/SW3 (Swedish genetic lineage). In contrast to other genovar E strains, ddCT had identical alleles with seven out of seven loci found in ST13 strains of genovars D and G, including the founder for this clonal group, D/UW-3/CX, and six out of seven loci found in its derivatives, such as ST6, ST10, and ST95 of genovars G and H. Nevertheless, MSTree V2 showed that ddCT and nvCT could have a common early ancestor, which is a parental C.t. G/9301 strain of ST9. A significant difference between ddCT and nvCT of genovar D (nvCT-D) that was recently found in Mexico was also determined as: (i) ddCT belonged to genovar E but not to genovar D; (ii) ddCT had a 44 bp duplication within the orf3 of the plasmid typical for nvCT; (iii) ddCT possessed an additional 17 bp deletion in the orf1. In conclusion, improved case management should include the clinical physician’s awareness of the need to enhance molecular screening of asymptomatic Chlamydia patients. Such molecular diagnostics might be essential to significantly reducing the global burden of Chlamydial infection on international public health.

The Hidden Genomics of Chlamydia trachomatis

The application of whole-genome sequencing has moved us on from sequencing single genomes to defining unravelling population structures in different niches, and at the -species, -serotype or even -genus level, and in local, national and global settings. This has been instrumental in cataloguing and revealing a huge a range of diversity in this bacterium, when at first we thought there was little. Genomics has challenged assumptions, added insight, as well as confusion and glimpses of truths. What is clear is that at a time when we start to realise the extent and nature of the diversity contained within a genus or a species like this, the huge depth of knowledge communities have developed, through cell biology, as well as the new found molecular approaches will be more precious than ever to link genotype to phenotype. Here we detail the technological developments and insights we have seen during the relatively short time since we began to see the hidden genome of Chlamydia trachomatis.

Identification and Discrimination of Chlamydia trachomatis Ocular and Urogenital Strains and Major Phylogenetic Lineages by CtGEM Typing, A Double-Locus Genotyping Method

CtGEM typing was developed to subdivide the bacterial species Chlamydia trachomatis on the basis of genome phylogeny and anatomical tropism. The rationale was facilitation of surveillance for ocular strains, although the method is applicable to essentially any C. trachomatis surveillance application that does not require high resolution. CtGEM is a double-locus genotyping method. The loci included in the assay were identified by computerized analysis of 65 complete genomes for resolution optimized sets of single nucleotide polymorphisms (SNPs). From this, two PCR amplifiable fragments were defined. One, rg1, is within a hypothetical gene annotated as Jali-1891 within the C. trachomatis B_Jali20 genome. The other, ofr, is within the ompA gene which encodes the major outer membrane protein. Variation in rg1 is conferred by two SNPs defining four haplotypes that exhibit concordance with genome phylogeny. Variation within ofr is more complex and allows for inference of ompA genotype, either to the level of single genotype, or group of closely related genotypes. Two CtGEM formats were developed. One is based on interrogation of the two loci by high resolution melting analysis (HRMA), and the other based on analysis of the loci by Sanger sequencing. The genotypes defined identify known ocular genotypes, discriminate known ocular genotypes from each other, discriminate the major phylogenetic lineages of the species, and discriminate all ompA genotypes with the exception of closely related variants within the genotypes H, I, J cluster. The Sanger sequencing format provides slightly more resolution that the HRMA format with respect to ompA genotype. An unusual aspect of this method is that all possible combinations of rg1 haplotype, and inferred ompA genotype(s) have been given CtGEM typing numbers. This includes types that at this time have not been shown to exist.

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.

Genome sequencing of Chlamydia trachomatis serovars E and F reveals substantial genetic variation

Chlamydia trachomatis (Ctr) is a bacterial pathogen that causes ocular, urogenital and lymph system infections in humans. It is highly abundant and among its serovars, E, F and D are most prevalent in sexually transmitted disease. However, the number of publicly available genome sequences of the serovars E and F, and thereby our knowledge about the molecular architecture of these serovars, is low. Here we sequenced the genomes of six E and F clinical isolates and one E lab strain, in order to study the genetic variance in these serovars. As observed before, the genomic variation inside the Ctr genomes is very low and the phylogenetic placement in comparison to publicly available genomes is as expected by ompA gene serotyping. However, we observed a large InDel carrying four to five open reading frames in one clinical E sample and in the E lab strain. We have also observed substantial variation on nucleotide and amino acid levels, especially in membrane proteins and secreted proteins. Furthermore, these two groups of proteins are also target for recombination events. One clinical F isolate was genetically heterogeneous and revealed the highest differences on nucleotide level in the pmpE gene.

Chlamydia muridarum Genital and Gastrointestinal Infection Tropism Is Mediated by Distinct Chromosomal Factors

Some members of the genus Chlamydia, including the human pathogen Chlamydia trachomatis, infect multiple tissues, including the genital and gastrointestinal (GI) tracts. However, it is unknown if bacterial targeting to these sites is mediated by multifunctional or distinct chlamydial factors. We previously showed that disruption of individual large clostridial toxin homologs encoded within the Chlamydia muridarum plasticity zone were not critical for murine genital tract infection. Here, we assessed whether cytotoxin genes contribute to C. muridarum GI tropism. Infectivity and shedding of wild-type (WT) C. muridarum and three mutants containing nonsense mutations in different cytotoxin genes, tc0437, tc0438, and tc0439, were compared in mouse genital and GI infection models. One mutant, which had a nonsense mutation in tc0439, was highly attenuated for GI infection and had a GI 50% infectious dose (ID50) that was 1,000 times greater than that of the WT. GI inoculation with this mutant failed to elicit anti-chlamydial antibodies or to protect against subsequent genital tract infection. Genome sequencing of the tc0439 mutant revealed additional chromosomal mutations, and phenotyping of additional mutants suggested that the GI attenuation might be linked to a nonsense mutation in tc0600 The molecular mechanism underlying this dramatic difference in tissue-tropic virulence is not fully understood. However, isolation of these mutants demonstrates that distinct chlamydial chromosomal factors mediate chlamydial tissue tropism and provides a basis for vaccine initiatives to isolate chlamydia strains that are attenuated for genital infection but retain the ability to colonize the GI tract and elicit protective immune responses.

CtGEM typing: Discrimination of Chlamydia trachomatis ocular and urogenital strains and major evolutionary lineages by high resolution melting analysis of two amplified DNA fragments

Chlamydia trachomatis infects the urogenital tract (UGT) and eyes. Anatomical tropism is correlated with variation in the major outer membrane protein encoded by ompA. Strains possessing the ocular ompA variants A, B, Ba and C are typically found within the phylogenetically coherent “classical ocular lineage”. However, variants B, Ba and C have also been found within three distinct strains in Australia, all associated with ocular disease in children and outside the classical ocular lineage. CtGEM genotyping is a method for detecting and discriminating ocular strains and also the major phylogenetic lineages. The rationale was facilitation of surveillance to inform responses to C. trachomatis detection in UGT specimens from young children. CtGEM typing is based on high resolution melting analysis (HRMA) of two PCR amplified fragments with high combinatorial resolving power, as defined by computerised comparison of 65 whole genomes. One fragment is from the hypothetical gene defined by Jali-1891 in the C. trachomatis B_Jali20 genome, while the other is from ompA. Twenty combinatorial CtGEM types have been shown to exist, and these encompass unique genotypes for all known ocular strains, and also delineate the TI and T2 major phylogenetic lineages, identify LGV strains and provide additional resolution beyond this. CtGEM typing and Sanger sequencing were compared with 42 C. trachomatis positive clinical specimens, and there were no disjunctions. CtGEM typing is a highly efficient method designed and tested using large scale comparative genomics. It divides C. trachomatis into clinically and biologically meaningful groups, and may have broad application in surveillance.

Population-based analysis of ocular Chlamydia trachomatis in trachoma-endemic West African communities identifies genomic markers of disease severity

BACKGROUND

Chlamydia trachomatis (Ct) is the most common infectious cause of blindness and bacterial sexually transmitted infection worldwide. Ct strain-specific differences in clinical trachoma suggest that genetic polymorphisms in Ct may contribute to the observed variability in severity of clinical disease.

METHODS

Using Ct whole genome sequences obtained directly from conjunctival swabs, we studied Ct genomic diversity and associations between Ct genetic polymorphisms with ocular localization and disease severity in a treatment-naïve trachoma-endemic population in Guinea-Bissau, West Africa.

RESULTS

All Ct sequences fall within the T2 ocular clade phylogenetically. This is consistent with the presence of the characteristic deletion in trpA resulting in a truncated non-functional protein and the ocular tyrosine repeat regions present in tarP associated with ocular tissue localization. We have identified 21 Ct non-synonymous single nucleotide polymorphisms (SNPs) associated with ocular localization, including SNPs within pmpD (odds ratio, OR = 4.07, p* = 0.001) and tarP (OR = 0.34, p* = 0.009). Eight synonymous SNPs associated with disease severity were found in yjfH (rlmB) (OR = 0.13, p* = 0.037), CTA0273 (OR = 0.12, p* = 0.027), trmD (OR = 0.12, p* = 0.032), CTA0744 (OR = 0.12, p* = 0.041), glgA (OR = 0.10, p* = 0.026), alaS (OR = 0.10, p* = 0.032), pmpE (OR = 0.08, p* = 0.001) and the intergenic region CTA0744-CTA0745 (OR = 0.13, p* = 0.043).

CONCLUSIONS

This study demonstrates the extent of genomic diversity within a naturally circulating population of ocular Ct and is the first to describe novel genomic associations with disease severity. These findings direct investigation of host-pathogen interactions that may be important in ocular Ct pathogenesis and disease transmission.

Genomic analyses of the Chlamydia trachomatis core genome show an association between chromosomal genome, plasmid type and disease

Background

Chlamydia trachomatis (Ct) plasmid has been shown to encode genes essential for infection. We evaluated the population structure of Ct using whole-genome sequence data (WGS). In particular, the relationship between the Ct genome, plasmid and disease was investigated.

Results

WGS data from 157 Ct isolates deposited in the Chlamydiales pubMLST database (http://pubMLST.org/chlamydiales/) were annotated with 902 genes including the core and accessory genome. Plasmid associated genes were annotated and a plasmid MLST scheme was defined allowing plasmid sequence types to be determined. Plasmid allelic variation was investigated. Phylogenetic relationships were examined using the Genome Comparator tool available in pubMLST. Phylogenetic analyses identified four distinct Ct core genome clusters and six plasmid clusters, with a strong association between the chromosomal genotype and plasmid. This in turn was linked to ompA genovars and disease phenotype. Horizontal genetic transfer of plasmids was observed for three urogenital-associated isolates, which possessed plasmids more commonly found in isolates resulting from ocular infections. The pgp3 gene was identified as the most polymorphic plasmid gene and pgp4 was the most conserved.

Conclusion

A strong association between chromosomal genome, plasmid type and disease was observed, consistent with previous studies. This suggests co-evolution of the Ct chromosome and their plasmids, but we confirmed that plasmid transfer can occur between isolates. These data provide a better understanding of the genetic diversity occurring across the Ct genome in association with the plasmid content.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-4522-3) contains supplementary material, which is available to authorized users.

Transformation of Chlamydia: current approaches and impact on our understanding of chlamydial infection biology

The intonation "The king is dead, long live the king" aptly describes the state of Chlamydia research. Genetic-based approaches are rapidly replacing correlative strategies to provide new insights. We describe how current transformation technologies are enhancing progress in understanding Chlamydia infection biology and present key opportunities for further development.

Development of a Chlamydia suis-specific antibody enzyme-linked immunosorbent assay based on the use of a B-cell epitope of the polymorphic membrane protein C

Chlamydia suis infections lead to economic loss in the pork industry. Chlamydia suis infections could be successfully treated with tetracyclines until the appearance of a tetracycline resistant phenotype, which was acquired via horizontal gene transfer of the tet(C) gene. Given the importance of C. suis as a swine pathogen and as a recently emerged tetracycline resistant pathogen with zoonotic potential, our aim was to develop a sensitive C. suis-specific antibody ELISA based on the polymorphic membrane proteins (Pmps). Chlamydia Pmps are important virulence factors and candidate antigens for serodiagnosis. We identified nine Pmps (PmpA to I) in C. suis strain MD56 using a recently developed Hidden-Markov model. PmpC was the most promising candidate for the development of a C. suis-specific antibody ELISA as the protein was absent in C. abortus, C. pecorum and C. psittaci which also infect pigs and as the protein contained C. suis-specific amino acid regions, absent in C. trachomatis PmpC. We identified an immunodominant B-cell epitope in C. suis PmpC using experimental porcine sera. The sensitivity and specificity of the PmpC ELISA was compared to the complement fixation test (CFT) and to a recombinant MOMP ELISA using experimental sera. The PmpC ELISA detected all positive control sera and was in contrast to CFT and the rMOMP ELISA 100% C. suis specific as positive control sera against other Chlamydia species did not react in the PmpC ELISA. The test was successfully validated using slaughterhouse sera and sera from clinically affected pigs. The PmpC ELISA could assist in diminishing the spread of C. suis infections in the pork industry.

Lymphogranuloma venereum rates increased and Chlamydia trachomatis genotypes changed among men who have sex with men in Sweden 2004-2016

This study aimed to determine the incidence of lymphogranuloma venereum (LGV) in Sweden since 2004 and to study in detail a consecutive number of Chlamydia trachomatis cases in men who have sex with men (MSM) during a 10 month period (September 2014 to July 2015). LGV increased from sporadic import cases in 2004 to comprise a spread within Sweden in 2016. Initially, only the L2b ompA genotype was detected, but in 2015 half of the genotyped LGV cases were L2 genotype. The changing genotype distribution in Sweden is linked to increased LGV spread in Europe. High-resolution multilocus sequence typing of 168 C. trachomatis cases from MSM in 2015 resulted in 29 sequence types, of which 3 accounted for 49 % of cases. The increased rates and different genotypes of LGV indicate that more concern for high-risk taking MSM is needed to avoid further spread of this invasive infection.

Demonstration of Persistent Infections and Genome Stability by Whole-Genome Sequencing of Repeat-Positive, Same-Serovar Chlamydia trachomatis Collected From the Female Genital Tract

Background

The biology of recurrent or long-term infections of humans by Chlamydia trachomatis is poorly understood. Because repeated or persistent infections are correlated with serious complications in humans, understanding these processes may improve clinical management and public health disease control.

Methods

We conducted whole-genome sequence analysis on C. trachomatis isolates collected from a previously described patient set in which individuals were shown to be infected with a single serovar over a lengthy period.

Results

Data from 5 of 7 patients showed compelling evidence for the ability of these patients to harbor the same strain for 3-5 years. Mutations in these strains were cumulative, very uncommon, and not linked to any single protein or pathway. Serovar J strains isolated from 1 patient 3 years apart did not accumulate a single base change across the genome. In contrast, the sequence results of 2 patients, each infected only with serovar Ia strains, revealed multiple same-serovar infections over 1-5 years.

Conclusions

These data demonstrate examples of long-term persistence in patients in the face of repeated antibiotic therapy and show that pathogen mutational strategies are not important in persistence of this pathogen in patients.

Molecular Genetic Analysis of Chlamydia Species

Species of Chlamydia are the etiologic agent of endemic blinding trachoma, the leading cause of bacterial sexually transmitted diseases, significant respiratory pathogens, and a zoonotic threat. Their dependence on an intracellular growth niche and their peculiar developmental cycle are major challenges to elucidating their biology and virulence traits. The last decade has seen tremendous advances in our ability to perform a molecular genetic analysis of Chlamydia species. Major achievements include the generation of large collections of mutant strains, now available for forward- and reverse-genetic applications, and the introduction of a system for plasmid-based transformation enabling complementation of mutations; expression of foreign, modified, or reporter genes; and even targeted gene disruptions. This review summarizes the current status of the molecular genetic toolbox for Chlamydia species and highlights new insights into their biology and new challenges in the nascent field of Chlamydia genetics.

Spread of a new Chlamydia trachomatis variant from men who have sex with men to the heterosexual population after replacement and recombination in ompA and pmpH genes

OBJECTIVES

Sexually transmitted infections are frequently related to outbreaks in high-risk populations due to the dense sexual networks. We wanted to determine the dissemination of a Chlamydia trachomatis variant characterized by the pmpH-recombinant gene between L and G genotypes, which was previously described in a high-risk population.

METHODS

A total of 449 samples were analysed in two periods ranging from 2009 to 2015 for detection of the pmpH-recombinant gene. For those samples yielding positive amplification, a sampling was selected for phylogenetic reconstructions based on sequencing of five chromosomal genes.

RESULTS

Globally this variant was found in 113 of the 449 samples (25%). During the first years (2009-13), this variant was found almost exclusively in rectal samples (30/112 samples) of men who have sex with men and in only one non-rectal sample (1/63). In 2014, this variant was also found in urethral and pharyngeal samples (1/24 and 1/7, respectively). However, in 2015, an epidemiological change was observed as the proportion of this variant had increased in rectal samples (20/51; 39%) and non-rectal samples, including cervical samples (51/142; 36.4%). The molecular characterization revealed the replacement of the ompA gene belonging to subtype G in samples recovered from 2009 to 2013 by the ompA gene belonging to subtype J after 2013.

CONCLUSIONS

Our data would support the evidence that subtype J could be a 'subtype bridge' between different sexual networks, as subtype J has been found in men who have sex with men and heterosexual populations in similar proportions. This work reveals the necessity of implementing molecular surveillance in extra-rectal samples to help us understand the gaps in transmission.

Tet(C) Gene Transfer between Chlamydia suis Strains Occurs by Homologous Recombination after Co-infection: Implications for Spread of Tetracycline-Resistance among Chlamydiaceae

Chlamydia suis is a swine pathogen that has also recently been found to cause zoonotic infections of the human eye, pharynx, and gastrointestinal tract. Many strains contain a tetracycline class C gene [tet(C)] cassette that confers tetracycline resistance. The cassette was likely originally acquired by horizontal gene transfer from a Gram-negative donor after the introduction of tetracycline into animal feed in the 1950s. Various research groups have described the capacity for different Chlamydia species to exchange DNA by homologous recombination. Since over 90% of C. suis strains are tetracycline resistant, they represent a potential source for antibiotic-resistance spread within and between Chlamydiaceae species. Here, we examined the genetics of tet(C)-transfer among C. suis strains. Tetracycline-sensitive C. suis strain S45 was simultaneously or sequentially co-infected with tetracycline-resistant C. suis strains in McCoy cells. Potential recombinants were clonally purified by a harvest assay derived from the classic plaque assay. C. suis strain Rogers132, lacking transposases IS200 and IS605, was the most efficient donor, producing two unique recombinants detected in three of the 56 (5.4%) clones screened. Recombinants were found to have a minimal inhibitory concentration (MIC) of 8-16 μg/mL for tetracycline. Resistance remained stable over 10 passages as long as recombinants were initially grown in tetracycline at twice the MIC of S45 (0.032 μg/mL). Genomic analysis revealed that tet(C) had integrated into the S45 genome by homologous recombination at two unique sites depending on the recombinant: a 55 kb exchange between nrqF and pckG, and a 175 kb exchange between kdsA and cysQ. Neither site was associated with inverted repeats or motifs associated with recombination hotspots. Our findings show that cassette transfer into S45 has low frequency, does not require IS200/IS605 transposases, is stable if initially grown in tetracycline, and results in multiple genomic configurations. We provide a model for stable cassette transfer to better understand the capability for cassette acquisition by Chlamydiaceae species that infect humans, a matter of public health importance.

Advances and Obstacles in the Genetic Dissection of Chlamydial Virulence

Obligate intracellular pathogens in the family Chlamydiaceae infect taxonomically diverse eukaryotes ranging from amoebae to mammals. However, many fundamental aspects of chlamydial cell biology and pathogenesis remain poorly understood. Genetic dissection of chlamydial biology has historically been hampered by a lack of genetic tools. Exploitation of the ability of chlamydia to recombine genomic material by lateral gene transfer (LGT) ushered in a new era in chlamydia research. With methods to map mutations in place, genetic screens were able to assign functions and phenotypes to specific chlamydial genes. Development of an approach for stable transformation of chlamydia also provided a mechanism for gene delivery and platforms for disrupting chromosomal genes. Here, we explore how these and other tools have been used to test hypotheses concerning the functions of known chlamydial virulence factors and discover the functions of completely uncharacterized genes. Refinement and extension of the existing genetic tools to additional Chlamydia spp. will substantially advance understanding of the biology and pathogenesis of this important group of pathogens.

The Number, Organization, and Size of Polymorphic Membrane Protein Coding Sequencesas well as the Most Conserved Pmp Protein Differ within and across Species

Variation is a central trait of the polymorphic membrane protein (Pmp) family. The number of <i>pmp</i> coding sequences differs between <i>Chlamydia</i> species, but it is unknown whether the number of <i>pmp</i> coding sequences is constant within a <i>Chlamydia</i> species. The level of conservation of the Pmp proteins has previously only been determined for <i>Chlamydia trachomatis.</i> As different Pmp proteins might be indispensible for the pathogenesis of different <i>Chlamydia </i>species, this study investigated the conservation of Pmp proteins both within and across <i>C. trachomatis,</i><i>C. pneumoniae,</i><i>C. abortus,</i> and <i>C. psittaci.</i> The <i>pmp</i> coding sequences were annotated in 16 <i>C. trachomatis,</i> 6 <i>C. pneumoniae,</i> 2 <i>C. abortus,</i> and 16 <i>C. psittaci</i> genomes. The number and organization of polymorphic membrane coding sequences differed within and across the analyzed <i>Chlamydia </i>species. The length of coding sequences of <i>pmpA,</i><i>pmpB,</i> and <i>pmpH</i> was conserved among all analyzed genomes, while the length of <i>pmpE/F</i> and <i>pmpG,</i> and remarkably also of the subtype <i>pmpD,</i> differed among the analyzed genomes. PmpD, PmpA, PmpH, and PmpA were the most conserved Pmp in <i>C. trachomatis,</i><i>C. pneumoniae,</i><i>C. abortus,</i> and <i>C. psittaci</i>, respectively. PmpB was the most conserved Pmp across the 4 analyzed <i>Chlamydia</i> species.

Emancipating Chlamydia: Advances in the Genetic Manipulation of a Recalcitrant Intracellular Pathogen

Chlamydia species infect millions of individuals worldwide and are important etiological agents of sexually transmitted disease, infertility, and blinding trachoma. Historically, the genetic intractability of this intracellular pathogen has hindered the molecular dissection of virulence factors contributing to its pathogenesis. The obligate intracellular life cycle of Chlamydia and restrictions on the use of antibiotics as selectable markers have impeded the development of molecular tools to genetically manipulate these pathogens. However, recent developments in the field have resulted in significant gains in our ability to alter the genome of Chlamydia, which will expedite the elucidation of virulence mechanisms. In this review, we discuss the challenges affecting the development of molecular genetic tools for Chlamydia and the work that laid the foundation for recent advancements in the genetic analysis of this recalcitrant pathogen.

Chlamydia trachomatis from Australian Aboriginal people with trachoma are polyphyletic composed of multiple distinctive lineages

Chlamydia trachomatis causes sexually transmitted infections and the blinding disease trachoma. Current data on C. trachomatis phylogeny show that there is only a single trachoma-causing clade, which is distinct from the lineages causing urogenital tract (UGT) and lymphogranuloma venerum diseases. Here we report the whole-genome sequences of ocular C. trachomatis isolates obtained from young children with clinical signs of trachoma in a trachoma endemic region of northern Australia. The isolates form two lineages that fall outside the classical trachoma lineage, instead being placed within UGT clades of the C. trachomatis phylogenetic tree. The Australian trachoma isolates appear to be recombinants with UGT C. trachomatis genome backbones, in which loci that encode immunodominant surface proteins (ompA and pmpEFGH) have been replaced by those characteristic of classical ocular isolates. This suggests that ocular tropism and association with trachoma are functionally associated with some sequence variants of ompA and pmpEFGH.

Chlamydia trachomatis isolates causing a blinding disease (trachoma) form a single lineage that is different from the lineages causing urogenital infections. Here, Andersson et al. show however that trachoma isolates from Australia are more closely related to urogenital strains than to other trachoma isolates.

Gene Deletion by Fluorescence-Reported Allelic Exchange Mutagenesis in Chlamydia trachomatis

Although progress in Chlamydia genetics has been rapid, genomic modification has previously been limited to point mutations and group II intron insertions which truncate protein products. The bacterium has thus far been intractable to gene deletion or more-complex genomic integrations such as allelic exchange. Herein, we present a novel suicide vector dependent on inducible expression of a chlamydial gene that renders Chlamydia trachomatis fully genetically tractable and permits rapid reverse genetics by fluorescence-reported allelic exchange mutagenesis (FRAEM). We describe the first available system of targeting chlamydial genes for deletion or allelic exchange as well as curing plasmids from C. trachomatis serovar L2. Furthermore, this approach permits the monitoring of mutagenesis by fluorescence microscopy without disturbing bacterial growth, a significant asset when manipulating obligate intracellular organisms. As proof of principle, trpA was successfully deleted and replaced with a sequence encoding both green fluorescent protein (GFP) and β-lactamase. The trpA-deficient strain was unable to grow in indole-containing medium, and this phenotype was reversed by complementation with trpA expressed in trans. To assess reproducibility at alternate sites, FRAEM was repeated for genes encoding type III secretion effectors CTL0063, CTL0064, and CTL0065. In all four cases, stable mutants were recovered one passage after the observation of transformants, and allelic exchange was limited to the specific target gene, as confirmed by whole-genome sequencing. Deleted sequences were not detected by quantitative real-time PCR (qPCR) from isogenic mutant populations. We demonstrate that utilization of the chlamydial suicide vector with FRAEM renders C. trachomatis highly amenable to versatile and efficient genetic manipulation.

The obligate intracellular nature of a variety of infectious bacteria presents a significant obstacle to the development of molecular genetic tools for dissecting pathogenicity. Although progress in chlamydial genetics has been rapid, genomic modification has previously been limited to point mutations and group II intron insertions which truncate protein products. The bacterium has thus far been intractable to gene deletion or more-complex genomic integrations such as allelic exchange. Here, we present a novel suicide vector dependent on inducible expression of a chlamydial gene that renders Chlamydia trachomatis fully genetically tractable and permits rapid reverse genetics by fluorescence-reported allelic exchange mutagenesis (FRAEM). We describe the first available system of targeting chlamydial genes for deletion or allelic exchange as well as curing plasmids from C. trachomatis L2. Furthermore, this approach permits monitoring of mutagenesis by fluorescence microscopy without disturbing bacterial growth, a significant asset when manipulating obligate intracellular organisms.

A Coming of Age Story: Chlamydia in the Post-Genetic Era

Chlamydia spp. are ubiquitous, obligate, intracellular Gram-negative bacterial pathogens that undergo a unique biphasic developmental cycle transitioning between the infectious, extracellular elementary body and the replicative, intracellular reticulate body. The primary Chlamydia species associated with human disease are C. trachomatis, which is the leading cause of both reportable bacterial sexually transmitted infections and preventable blindness, and C. pneumoniae, which infects the respiratory tract and is associated with cardiovascular disease. Collectively, these pathogens are a significant source of morbidity and pose a substantial financial burden on the global economy. Past efforts to elucidate virulence mechanisms of these unique and important pathogens were largely hindered by an absence of genetic methods. Watershed studies in 2011 and 2012 demonstrated that forward and reverse genetic approaches were feasible with Chlamydia and that shuttle vectors could be selected and maintained within the bacterium. While these breakthroughs have led to a steady expansion of the chlamydial genetic tool kit, there are still roads left to be traveled. This minireview provides a synopsis of the currently available genetic methods for Chlamydia along with a comparison to the methods used in other obligate intracellular bacteria. Limitations and advantages of these techniques will be discussed with an eye toward the methods still needed, and how the current state of the art for genetics in obligate intracellular bacteria could direct future technological advances for Chlamydia.

Human and Pathogen Factors Associated with Chlamydia trachomatis-Related Infertility in Women

Chlamydia trachomatis is the most common bacterial sexually transmitted pathogen worldwide. Infection can result in serious reproductive pathologies, including pelvic inflammatory disease, ectopic pregnancy, and infertility, in women. However, the processes that result in these reproductive pathologies have not been well defined. Here we review the evidence for the human disease burden of these chlamydial reproductive pathologies. We then review human-based evidence that links Chlamydia with reproductive pathologies in women. We present data supporting the idea that host, immunological, epidemiological, and pathogen factors may all contribute to the development of infertility. Specifically, we review the existing evidence that host and pathogen genotypes, host hormone status, age of sexual debut, sexual behavior, coinfections, and repeat infections are all likely to be contributory factors in development of infertility. Pathogen factors such as infectious burden, treatment failure, and tissue tropisms or ascension capacity are also potential contributory factors. We present four possible processes of pathology development and how these processes are supported by the published data. We highlight the limitations of the evidence and propose future studies that could improve our understanding of how chlamydial infertility in women occurs and possible future interventions to reduce this disease burden.

TLR2, TLR4 and TLR9 genotypes and haplotypes in the susceptibility to and clinical course of Chlamydia trachomatis infections in Dutch women

Chlamydia trachomatis infections demonstrate remarkable differences in clinical course that are approximately 40% based on host genetic variation. Here, we study the single nucleotide polymorphisms (SNPs) and their haplotypes in TLR2, TLR4 and TLR9 (TLR2 +2477G>A; TLR2 -16934T>A; TLR4+896A>G; TLR9 -1237T>C and TLR9 +2848G>A) in relation to the susceptibility to, and severity of C. trachomatis infections. We analysed the five SNPs in a cohort of 770 Dutch Caucasian women either attending a sexually transmitted diseases outpatient clinic (n = 731) or having complaints of subfertility (n = 39). Haplotype analyses showed a trend for TLR2 haplotype I (-16934T/+2477G) to protect against the development of symptoms and tubal pathology (Ptrend = 0.03) after Chlamydia infection. In the susceptibility cohort, TLR9 haplotype III (-1237C/+2848A) showed a significant decreasing trend in the development of symptoms after C. trachomatis infection (P = 0.02, OR: 0.55, 95%CI: 0.33-0.91). Logistic regression of the TLR2 haplotypes, TLR4+896A>G, and TLR9 haplotypes showed that the TLR2 haplotype combinations AG-TA and AG-TG confer risk (OR 3.4 (P = 0.01) and 1.6 (P = 0.03)), while the TLR9 haplotype combination TG-TA protects against C. trachomatis infections (OR: 0.4, P = 0.004). Our study shows that both TLR2 and TLR9 genes and SNP combinations do influence the clinical course of Chlamydia infections.

Chlamydial Lytic Exit from Host Cells Is Plasmid Regulated

Chlamydia trachomatis is an obligate intracellular bacterium that is a globally important human pathogen. The chlamydial plasmid is an attenuating virulence factor, but the molecular basis for attenuation is not understood. Chlamydiae replicate within a membrane-bound vacuole termed an inclusion, where they undergo a biphasic developmental growth cycle and differentiate from noninfectious into infectious organisms. Late in the developmental cycle, the fragile chlamydia-laden inclusion retains its integrity by surrounding itself with scaffolds of host cytoskeletal proteins. The ability of chlamydiae to developmentally free themselves from this cytoskeleton network is a fundamental virulence trait of the pathogen. Here, we show that plasmidless chlamydiae are incapable of disrupting their cytoskeletal entrapment and remain intracellular as stable mature inclusions that support high numbers of infectious organisms. By using deletion mutants of the eight plasmid-carried genes (Δpgp1 to Δpgp8), we show that Pgp4, a transcriptional regulator of multiple chromosomal genes, is required for exit. Exit of chlamydiae is dependent on protein synthesis and is inhibited by the compound C1, an inhibitor of the type III secretion system (T3S). Exit of plasmid-free and Δpgp4 organisms, which failed to lyse infected cells, was rescued by latrunculin B, an inhibitor of actin polymerization. Our findings describe a genetic mechanism of chlamydial exit from host cells that is dependent on an unknown pgp4-regulated chromosomal T3S effector gene.

IMPORTANCE

Chlamydia's obligate intracellular life style requires both entry into and exit from host cells. Virulence factors that function in exiting are unknown. The chlamydial inclusion is stabilized late in the infection cycle by F-actin. A prerequisite of chlamydial exit is its ability to disassemble actin from the inclusion. We show that chlamydial plasmid-free organisms, and also a plasmid gene protein 4 (pgp4) null mutant, do not disassociate actin from the inclusion and fail to exit cells. We further provide evidence that Pgp4-regulated exit is dependent on the chlamydial type III secretion system. This study is the first to define a genetic mechanism that functions in chlamydial lytic exit from host cells. The findings also have practical implications for understanding why plasmid-free chlamydiae are highly attenuated and have the ability to elicit robust protective immune responses.

Chlamydiaceae Genomics Reveals Interspecies Admixture and the Recent Evolution of Chlamydia abortus Infecting Lower Mammalian Species and Humans

Chlamydiaceae are obligate intracellular bacteria that cause a diversity of severe infections among humans and livestock on a global scale. Identification of new species since 1989 and emergence of zoonotic infections, including abortion in women, underscore the need for genome sequencing of multiple strains of each species to advance our knowledge of evolutionary dynamics across Chlamydiaceae. Here, we genome sequenced isolates from avian, lower mammalian and human hosts. Based on core gene phylogeny, five isolates previously classified as Chlamydia abortus were identified as members of Chlamydia psittaci and Chlamydia pecorum. Chlamydia abortus is the most recently emerged species and is a highly monomorphic group that lacks the conserved virulence-associated plasmid. Low-level recombination and evidence for adaptation to the placenta echo evolutionary processes seen in recently emerged, highly virulent niche-restricted pathogens, such as Bacillus anthracis. In contrast, gene flow occurred within C. psittaci and other Chlamydiaceae species. The C. psittaci strain RTH, isolated from a red-tailed hawk (Buteo jamaicensis), is an outlying strain with admixture of C. abortus, C. psittaci, and its own population markers. An average nucleotide identity of less than 94% compared with other Chlamydiaceae species suggests that RTH belongs to a new species intermediary between C. psittaci and C. abortus. Hawks, as scavengers and predators, have extensive opportunities to acquire multiple species in their intestinal tract. This could facilitate transformation and homologous recombination with the potential for new species emergence. Our findings indicate that incubator hosts such as birds-of-prey likely promote Chlamydiaceae evolution resulting in novel pathogenic lineages.

Highly diverse MLVA-ompA genotypes of rectal Chlamydia trachomatis among men who have sex with men in Brighton, UK and evidence for an HIV-related sexual network

OBJECTIVES

In this prospective study, we aimed to determine the distribution of genotypes by multilocus variable number tandem repeat (VNTR) analysis plus analysis of the ompA gene (MLVA-ompA) of rectal Chlamydia trachomatis among men who have sex with men (MSM) attending Brighton Genitourinary Medicine (GUM) Clinic and to examine any correlations with clinical variables, including HIV status, and to isolate rectal C. trachomatis cultures maximising the possibility of obtaining complete genotyping data.

METHODS

Samples were assigned genotypes by PCR and sequencing of the markers of the MLVA-ompA genotyping system. Rectal C. trachomatis was isolated in cell culture using McCoy cells. Data regarding demographics, HIV status, rectal symptoms and history of sexually transmitted infections, including C. trachomatis, were collected.

RESULTS

1809 MSM attending the clinic between October 2011 and January 2013 took part in the study, 112 (6.2%) of whom had rectal samples that tested positive for C. trachomatis. 85/112 (75.9%) C. trachomatis-positive rectal samples were assigned 66 different genotypes. Two distinct genotype subclusters were identified: subcluster 1 consisted of more HIV-negative men than subcluster 2 (p=0.025), and the MLVA-ompA genotypes in these subclusters reflected this. Isolates were successfully cultured from 37 of the 112 specimens, from which 27 otherwise unobtainable (from direct PCR) MLVA-ompA genotypes were gained.

CONCLUSIONS

The most prevalent genotypes were G, E and D representing some overlap with the heterosexual distribution in UK. Subcluster 1 consisted of more 'heterosexual genotypes' and significantly more HIV-negative men than subcluster 2, associated with 'MSM genotypes'. There was a higher diversity of C. trachomatis strains among MSM in Brighton than observed in other cities.

Genome expansion in bacteria: the curios case of Chlamydia trachomatis

Background

Recent findings indicated that a correlation between genomic % AT and genome size within strains of microbial species was predominantly associated with the uptake of foreign DNA. One species however, Chlamydia trachomatis, defied any explanation. In the present study 79 fully sequenced C. trachomatis genomes, representing ocular- (nine strains), urogenital- (36 strains) and lymphogranuloma venereum strains (LGV, 22 strains), in three pathogroups, in addition to 12 laboratory isolates, were scrutinized with the intent of elucidating the positive correlation between genomic AT content and genome size.

Results

The average size difference between the strains of each pathogroup was largely explained by the incorporation of genetic fragments. These fragments were slightly more AT rich than their corresponding host genomes, but not enough to justify the difference in AT content between the strains of the smaller genomes lacking the fragments. In addition, a genetic region predominantly found in the ocular strains, which had the largest genomes, was on average more GC rich than the host genomes of the urogenital strains (58.64 % AT vs. 58.69 % AT), which had the second largest genomes, implying that the foreign genetic regions cannot alone explain the association between genome size and AT content in C. trachomatis. 23,492 SNPs were identified for all 79 genomes, and although the SNPs were on average slightly GC rich (~47 % AT), a significant association was found between genome-wide SNP AT content, for each pathogroup, and genome size (p < 0.001, R² = 0.86) in the C. trachomatis strains.

Conclusions

The correlation between genome size and AT content, with respect to the C. trachomatis pathogroups, was explained by the incorporation of genetic fragments unique to the ocular and/or urogenital strains into the LGV- and urogential strains in addition to the genome-wide SNP AT content differences between the three pathogroups.

Electronic supplementary material

The online version of this article (doi:10.1186/s13104-015-1464-6) contains supplementary material, which is available to authorized users.

A characteristic of polymorphic membrane protein F of Chlamydia trachomatis isolated from male urogenital tracts in Japan

Although sexually transmitted disease due to Chlamydia trachomatis occurs similarly in both men and women, the female urogenital tract differs from that of males anatomically and physiologically, possibly leading to specific polymorphisms of the bacterial surface molecules. In the present study, we therefore characterized polymorphic features in a high-definition phylogenetic marker, polymorphic outer membrane protein (Pmp) F of C. trachomatis strains isolated from male urogenital tracts in Japan (Category: Japan-males, n = 12), when compared with those isolated from female cervical ducts in Japan (Category: Japan-females, n = 11), female cervical ducts in the other country (Category: Ref-females, n = 12) or homosexual male rectums in the other country (Category: Ref-males, n = 7), by general bioinformatics analysis tool with MAFFT software. As a result, phylogenetic reconstruction of the PmpF amino acid sequences showing three distinct clusters revealed that the Japan-males were limited into cluster 1 and 2, although there were only four clusters even though including an outgroup. Meanwhile, the phylogenetic distance values of PmpF passenger domain without hinge region, but not its full-length sequence, showed that the Japan-males were more stable and displayed less diversity when compared with the other categories, supported by the sequence conservation features. Thus, PmpF passenger domain is a useful phylogenetic maker, and the phylogenic features indicate that C. trachomatis strains isolated from male urogenital tracts in Japan may be unique, suggesting an adaptation depending on selective pressure, such as the presence or absence of microbial flora, furthermore possibly connecting to sexual differentiation.

Trachoma and Ocular Chlamydial Infection in the Era of Genomics

Trachoma is a blinding disease usually caused by infection with Chlamydia trachomatis (Ct) serovars A, B, and C in the upper tarsal conjunctiva. Individuals in endemic regions are repeatedly infected with Ct throughout childhood. A proportion of individuals experience prolonged or severe inflammatory episodes that are known to be significant risk factors for ocular scarring in later life. Continued scarring often leads to trichiasis and in-turning of the eyelashes, which causes pain and can eventually cause blindness. The mechanisms driving the chronic immunopathology in the conjunctiva, which largely progresses in the absence of detectable Ct infection in adults, are likely to be multifactorial. Socioeconomic status, education, and behavior have been identified as contributing to the risk of scarring and inflammation. We focus on the contribution of host and pathogen genetic variation, bacterial ecology of the conjunctiva, and host epigenetic imprinting including small RNA regulation by both host and pathogen in the development of ocular pathology. Each of these factors or processes contributes to pathogenic outcomes in other inflammatory diseases and we outline their potential role in trachoma.