Virtual Poster 21st Lancefield International Symposium for Streptococci and Streptococcal Diseases 2022

Host-dependent resistance of Group A Streptococcus to sulfamethoxazole mediated by horizontally-acquired ECF transporter S component (#302)

Kalindu M. D. Rodrigo 1 , Aarti Saiganesh 1 , Andrew J. Hayes 2 , Jack Anstey 1 , Jua Iwasaki 1 , Janessa L. Pickering 1 , Jessica Hillas 1 , Scott Winslow 1 , Tabitha Woodman 1 , Jake A. Lacey 3 , Mark P. G. van der Linden 4 , Philip M. Giffard 5 6 , Steven Y. C. Tong 3 7 , Keith A. Stubbs 8 , Jonathan R. Carapetis 1 9 , Asha C. Bowen 1 9 , Mark R. Davies 2 , Timothy C. Barnett 1 10
  1. Wesfarmers Centre of Vaccines and Infectious Diseases, Telethon Kids Institute, University of Western Australia, Nedlands, Western Australia , Australia
  2. Department of Microbiology and Immunology, University of Melbourne at the Peter Doherty Institute for Infection and Immunity, Melbourne , Victoria , Australia
  3. Department of Infectious Diseases, University of Melbourne at the Peter Doherty Institute for Infection and Immunity, Melbourne , Victoria , Australia
  4. German National Reference Center for Streptococci, Institute of Medical Microbiology, University Hospital RWTH Aachen, Aachen, Germany
  5. Menzies School of Health Research, Charles Darwin University, Darwin , Northern Territory , Australia
  6. College of Health and Human Sciences, Charles Darwin University, Darwin, Northern Territory , Australia
  7. Victorian Infectious Diseases Service, The Royal Melbourne Hospital, at the Peter Doherty Institute for Infection and Immunity, Melbourne , Victoria , Australia
  8. School of Molecular Sciences, University of Western Australia, Nedlands, Western Australia, Australia
  9. Department of Infectious Diseases, Perth Children’s Hospital, Nedlands, Western Australia , Australia
  10. School of Biomedical Sciences, University of Western Australia, Nedlands, Western Australia, Australia

Background:

Co-trimoxazole, a combination of the two antibiotics trimethoprim and sulfamethoxazole, is used to treat skin sores caused by Group A Streptococcus (GAS). Co-trimoxazole inhibits the synthesis of tetrahydrofolate in bacteria which is required for bacterial DNA synthesis. While the genetic mechanisms of co-trimoxazole resistance remain poorly characterised in GAS, strains with reduced susceptibility to co-trimoxazole have been reported.

Method:

Antibiotic susceptibility testing was performed according to the EUCAST guidelines. Whole genome sequencing and genomic analysis were performed to identify the genetic determinants of resistance. In vitro forced evolution assays and metabolic rescue experiments were used to identify metabolite-dependent co-trimoxazole resistance.

Results:

We identified a novel gene (thfT) that encodes an energy-coupling factor (ECF) transporter substrate-binding component. ThfT enables GAS strains to acquire extracellular tetrahydrofolate and related compounds from the host and bypass the inhibitory action of sulfamethoxazole. thfT is likely acquired by horizontal gene transfer from related Streptococcus species (Streptococcus dysgalactiae subsp. equisimilis). In the presence of tetrahydrofolate, GAS strains that encode thfT alone conferred a very high level of sulfamethoxazole resistance (>5 mg/ml) and strains with both thfT and a trimethoprim resistance gene conferred high level of cotrimoxazole resistance.

Conclusions:

Resistance mediated by ThfT in GAS currently remains undetectable by routine phenotypic susceptibility tests and genotypic surveillance methods as it requires host metabolites for the activity. This study identified a completely new antibiotic resistance mechanism and this novel paradigm of antibiotic resistance could be used to investigate host-dependent antibiotic resistance in other medically important bacterial pathogens.