Poster Presentation BacPath 13: Molecular Analysis of Bacterial Pathogens Conference 2015

The elusive Chlamydia pecorum plasmid: Strain-specific virulence or harmless accessory? (#119)

Martina Jelocnik 1 , Nathan L. Bachmann 2 , Bernard Kaltenboeck 3 , Courtney Waugh 4 , Lucy Woolford 5 , Katherine N. Speight 5 , Amber Gillett 6 , Damien Higgins 7 , Cheyne Flanagan 8 , Garry S. Myers 9 , Peter Timms 4 , Adam Polkinghorne 4
  1. University of Sunshine Coast, Brisbane, QLD, Australia
  2. Centre for Animal Health Innovation, University of Sunshine Coast, Sippy Downs, QLD, Australia
  3. Department of Pathobiology, University of Auburn, Auburn, AL, United States
  4. Faculty of Science, Health, Education and Engineering, University of Sunshine Coast, Sippy Downs, QLD, Australia
  5. School of Animal and Veterinary Sciences, University of Adelaide, Adelaide, SA, Australia
  6. Australia Zoo Wildlife Hospital, Beerwah, QLD, Australia
  7. Faculty of Veterinary Science, University of New South Wales, Sydney, NSW, Australia
  8. Port Macquarie Koala Hospital, Port Macquarie, NSW, Australia
  9. Institute for Genome Sciences, University of Maryland, Baltimore, MD, United States

Chlamydia pecorum is a globally recognised pathogen of livestock and koalas. To date, comparative genomics of C. pecorum strains from sheep, cattle and koalas has revealed that only single nucleotide polymorphisms (SNPs) and a limited number of pseudogenes found only in koala strains appear to contribute to the genetic diversity and virulence of this pathogen [1, 2, 3]. Almost ubiquitous in chlamydial species [4], no plasmids were detected in these C. pecorum strains.

Using culture independent methods [5], we sequenced genomes of three pig C. pecorum strains in order to re-evaluate the genetic differences and to update the phylogenetic relationships between C. pecorum from each of the hosts. Comparative genomics revealed increased SNPs between strains from pigs and other hosts, and an additional full length copy of chlamydial toxin gene [2] in the pig polyarthritis isolate. Phylogenetic analyses clustered pig isolates into a distinct clade, highlighting the polyphyletic origin of C. pecorum in different livestock hosts.

Most surprising, we also discovered a full length plasmid in the pig C. pecorum genome. Using this novel C. pecorum plasmid (pCpec) sequence,  primer pairs were designed to a) develop a pCpec screening assay to evaluate the plasmid distribution in C. pecorum from different hosts ; and b) to characterise the sequences of pCpec from other hosts. pCpec screening showed that not all C. pecorum strains carry this plasmid, and if present, is more prevalent in the koala (80%) than livestock strains (33%). Phylogenies of an additional 16 pCpec from pigs, cattle, sheep and koala C. pecorum strains indicated similar levels of diversity and congruency with whole genome phylogenies.

This study provides further insight into the complexity of C. pecorum epidemiology and may open new opportunities for vaccine development since chlamydial plasmid proteins in other species are immunogenic and potentially important virulence factors [4].

  1. Sait, M. et al. 2014. Genome sequencing and comparative analysis of three Chlamydia pecorum strains associated with different pathogenic outcomes. BMC Genomics 15, 23.
  2. Bachmann, N. et al. 2014. Comparative genomics of koala, cattle and sheep strains of Chlamydia pecorum. BMC Genomics 15, 667.
  3. Bachmann, N. et al. 2015. Culture-independent genome sequencing of clinical samples reveals an unexpected heterogeneity of infections by Chlamydia pecorum. J. Clin. Microbiol. 53, 5.
  4. Rockey, D.D. 2011. Unraveling the basic biology and clinical significance of the chlamydial plasmid. J. Exp. Med. 208, 11.
  5. Christiansen, M.T. et al. 2014. Whole-genome enrichment and sequencing of Chlamydia trachomatis directly from clinical samples. BMC Infect. Dis. 14, 591.