The first genomic insight into Chlamydia psittaci sequence type (ST)24 from a healthy captive psittacine host in Australia demonstrates evolutionary proximity with strains from psittacine, human, and equine hosts

Chlamydia psittaci is a zoonotic pathogen that infects birds, humans, and other mammals. Notably, recent studies suggested the human-to-human transmission of C. psittaci, and this pathogen also causes equine reproductive loss in Australia. Molecular studies in Australia to date have focused on and described clonal sequence type (ST)24 strains infecting horses, wild psittacine, and humans. In contrast, the genetic identity of C. psittaci strains from captive psittacine hosts is scarce. In 2022, C. psittaci was detected in the faeces of a healthy captive blue-fronted parrot (Amazona aestiva). Genomic DNA was extracted and underwent whole-genome sequencing. Here we report the 1,160,701 bp circular chromosome of C. psittaci strain BF_amazon_parrot13 and the 7,553 bp circular plasmid pCpsBF_amazon_parrot13. Initial in silico multi-locus sequence typing and ompA genotyping revealed that BF_amazon_parrot13 belongs to the clonal ST24 lineage and has an ompA genotype A. Further context involved the genomes of 31 published ST24 strains, utilising a single-nucleotide variant (SNV) based clustering approach. Despite temporal, host, and biogeographical separation, a core-genome SNV-based phylogeny revealed that BF_amazon_parrot13 clustered in a distinct subcluster with seven C. psittaci strains from equines in Australia (maximum pairwise distance of 13 SNVs). BF_amazon_parrot13 represents the first complete C. psittaci ST24 genome from a captive psittacine in Australia. Furthermore, by using whole-genome sequencing to coordinate surveillance, we can also learn more about the possible health risks and routes of chlamydia transmission among people, livestock, wild animals, and domesticated animals.

Automated summary

This article reports the complete genome sequence of Chlamydia psittaci strain BF_amazon_parrot13, which was detected in the feces of a healthy captive parrot in Australia. Analysis revealed that BF_amazon_parrot13 belongs to the ST24 lineage and has an ompA genotype A. Genomic comparison showed that BF_amazon_parrot13 clusters with seven C. psittaci strains from equines in Australia. This study is important for understanding the health risks and transmission routes of chlamydia among humans and animals.