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Chlamydia Trachomatis: when the Virulence-Associated Genome Backbone Imports a Prevalence-Associated Major Antigen Signature

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Journal Article - Open Access

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National Institute of Health Lisbon Portugal

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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 tropismprevalence, 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 DDa strain, likely possessing the genomic backbone associated with the more prevalent urogenital genotypes T1 clade, to an LGV L2b strain. The hybrid L2bD-Da strain presents the adhesin and immunodominant antigen MOMP major outer membrane protein encoded by ompA

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