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

Surveying genetic markers of antibiotic resistance and genomic background in Chlamydia trachomatis: insights from a multiplex NGS-based approach in clinical strains from Portugal

OBJECTIVES

To survey genetic markers of potential antimicrobial resistance (AMR) to macrolides and fluoroquinolones among Chlamydia trachomatis-positive samples from the collection of the Portuguese National Reference Laboratory for Sexually Transmitted Infections (STIs), and explore a multiplex PCR approach coupled with NGS to provide complementary information regarding a strain's genomic backbone.

METHODS

A total of 502 C. trachomatis-positive samples, mostly anorectal exudates, were subjected to PCR and sequencing of five targets, including loci potentially driving AMR (23S rRNA, gyrA and parC) and loci potentially informative about a strain's genomic backbone with emphasis on differentiation of lymphogranuloma venereum (LGV)/non-LGV and L2/L2b (a 9 bp insertion in pmpH, a 74 bp insertion upstream from CT105 and the polymorphic CT442).

RESULTS

No samples evidenced 23S rRNA mutations recognizably linked to macrolide resistance. Three samples harboured the Ser83Ile mutation in GyrA putatively driving fluoroquinolone resistance: two recombinant L2-L2b/D-Da (0.4%) and one L2 (0.2%). The screened regions in pmpH, upstream CT105 and CT442 were fully concordant with LGV/non-LGV differentiation. As expected, the pmpH L2b-specific genetic trait locus was detected in all L2b and recombinant L2-L2b/D-Da ompA genotypes, but also in 96.0% of L2 specimens, which also likely possess an L2b genomic backbone. The insertion upstream from CT105 exhibited full LGV specificity, constituting a promising target for the development of rapid LGV diagnostic assays.

CONCLUSIONS

This study contributes to enhancing the knowledge of C. trachomatis molecular epidemiology, suggesting that the known genetic determinants of AMR are not disseminated in clinical C. trachomatis strains, and presents an exploratory approach that can be suitable for LGV/non-LGV and L2/L2b genomic background differentiation.

Distribution of Chlamydia trachomatis ompA-genotypes over three decades in Portugal

OBJECTIVES

Chlamydia trachomatis is classified into 15 major genotypes, A to L3, based on the diversity of ompA gene. Here, we evaluated and characterised the distribution and diversity of ompA-genotypes over 32 years (1990-2021) in Portugal.

METHODS

The collection of the Portuguese National Reference Laboratory for Sexually Transmitted Infections includes 5824 C. trachomatis-positive samples that were successfully ompA-genotyped between 1990 and 2021. An in-depth analysis of ompA-genotypes distribution across the years, as well as by biological sex, age and anatomical site of infection was performed.

RESULTS

ompA-genotype E was consistently the most frequently detected across the years, with a median frequency of 34.6%, followed by D/Da (17.6%), F (14.3%) and G (10.7%). The prevalence of lymphogranuloma venereum (LGV) genotypes (mostly L2, 62.0%, followed by L2b, 32.1%) increased since 2016, reaching the highest value in 2019 (20.9%). LGV, G and Da genotypes were associated with biological sex, specifically with being male, and were the most frequent among anorectal specimens (37.7%, 19.4% and 17.7%, respectively). Notably, LGV ompA-genotypes represented 38.9% of the male anorectal specimens since 2016, and were also detected among oropharynx and urogenital samples. ompA-genotype E was the most frequently detected at the oropharynx (28.6%) and urogenital (33.9%) sites during the study period, followed by D/Da (17.4%) and F (16.0%) in the urogenital specimens, and by G (26.1%) and D/Da (25.7%) in oropharynx specimens. Our data also highlight the emergence of the recombinant L2b/D-Da strain since 2017 (representing between 2.0% and 15.5% of LGV cases per year) and the non-negligible detection of ompA-genotype B in urogenital and anorectal specimens.

CONCLUSIONS

This study provides a comprehensive landscape of C. trachomatis molecular surveillance in Portugal, highlighting the continued relevance of ompA-genotyping as a complement to rapid LGV-specific detection tests. It also contributes to a deeper understanding of C. trachomatis epidemiology, diversity and pathogenicity.

Evaluation of Chlamydia trachomatis Genotypes in Endocervical Specimens by Sequence Analysis of ompA Gene among Women in Tehran

Tehran's actual prevalence of Chlamydia trachomatis (CT) and its genotypes are still unclear. Molecular typing of CT strains can provide essential epidemiological knowledge and contribute to improved control measures. In this study, we aimed to determine the prevalence of CT and its genotypes in the endocervical infections of females who attended the gynecology and infertility clinics in Tehran. A total of 291 women were tested for chlamydial infection by in-house PCR using specific primers for the CT cryptic plasmid. Nested PCR for amplification of the ompA gene in positive samples was carried out, genotyping was performed by sequencing this gene, and further phylogenetic analysis was conducted. Sexual infection by CT was observed in 10.3% (30/291) of the subjects, and the mean age of patients was 30.4. The ompA gene was sequenced in 27 samples, revealing E genotypes 40.7%, (n = 11), F 25.9%, (n = 7), G 18.5%, (n = 5), D 11.1%, (n = 3), and K 3.7%, (n = 1). This study emphasizes the importance of the diversity among CT genotypes in our studied population and the need for wide-screening the neglected bacterial infection among women in Tehran.

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.

Ongoing evolution of Chlamydia trachomatis lymphogranuloma venereum: exploring the genomic diversity of circulating strains

Lymphogranuloma venereum (LGV), the invasive infection of the sexually transmissible infection (STI) Chlamydia trachomatis, is caused by strains from the LGV biovar, most commonly represented by ompA-genotypes L2b and L2. We investigated the diversity in LGV samples across an international collection over seven years using typing and genome sequencing. LGV-positive samples (n=321) from eight countries collected between 2011 and 2017 (Spain n=97, Netherlands n=67, Switzerland n=64, Australia n=53, Sweden n=37, Hungary n=31, Czechia n=30, Slovenia n=10) were genotyped for pmpH and ompA variants. All were found to contain the 9 bp insertion in the pmpH gene, previously associated with ompA-genotype L2b. However, analysis of the ompA gene shows ompA-genotype L2b (n=83), ompA-genotype L2 (n=180) and several variants of these (n=52; 12 variant types), as well as other/mixed ompA-genotypes (n=6). To elucidate the genomic diversity, whole genome sequencing (WGS) was performed from selected samples using SureSelect target enrichment, resulting in 42 genomes, covering a diversity of ompA-genotypes and representing most of the countries sampled. A phylogeny of these data clearly shows that these ompA-genotypes derive from an ompA-genotype L2b ancestor, carrying up to eight SNPs per isolate. SNPs within ompA are overrepresented among genomic changes in these samples, each of which results in an amino acid change in the variable domains of OmpA (major outer membrane protein, MOMP). A reversion to ompA-genotype L2 with the L2b genomic backbone is commonly seen. The wide diversity of ompA-genotypes found in these recent LGV samples indicates that this gene is under immunological selection. Our results suggest that the ompA-genotype L2b genomic backbone is the dominant strain circulating and evolving particularly in men who have sex with men (MSM) populations.

Chlamydia trachomatis: when the virulence-associated genome backbone imports a prevalence-associated major antigen signature

Chlamydia trachomatis is the most prevalent sexually transmitted bacterium worldwide and the causative agent of trachoma. Its strains are classified according to their ompA genotypes, which are strongly linked to differential tissue tropism and disease outcomes [ocular disease, urogenital disease and lymphogranuloma venereum (LGV)]. While the genome-based species phylogenetic tree presents four main clades correlating with tropism/prevalence, namely ocular, LGV, urogenital T1 (more prevalent genotypes) and urogenital T2 (less prevalent genotypes), inter-clade exchange of ompA is considered a rare phenomenon probably mediating marked tropism alterations. An LGV epidemic, associated with the clonal expansion of the L2b genotype, has emerged in the last few decades, raising concerns particularly due to its atypical clinical presentation (ulcerative proctitis) and circulation among men who have sex with men (MSM). Here, we report an LGV outbreak, mostly affecting human immunodeficiency virus-positive MSM engaging in high-risk sexual practices, caused by an L2b strain with a rather unique non-LGV ompA signature that precluded the laboratory notification of this outbreak as LGV. C. trachomatis whole-genome capture and sequencing directly from clinical samples was applied to deeply characterize the genomic backbone of this novel LGV outbreak-causing clone. It revealed a chimeric genome structure due to the genetic transfer of ompA and four neighbouring genes from a serovar D/Da strain, likely possessing the genomic backbone associated with the more prevalent urogenital genotypes (T1 clade), to an LGV (L2b) strain. The hybrid L2b/D-Da strain presents the adhesin and immunodominant antigen MOMP (major outer membrane protein) (encoded by ompA) with an epitope repertoire typical of non-invasive genital strains, while keeping the genome-dispersed virulence fingerprint of a classical LGV strain. As previously reported for inter-clade ompA exchange among non-LGV clades, this novel C. trachomatis genomic mosaic involving a contemporary epidemiologically and clinically relevant LGV strain may have implications on its transmission, tissue tropism and pathogenic capabilities. The emergence of variants with epidemic and pathogenic potential highlights the need for more focused surveillance strategies to capture C. trachomatis evolution in action.