Oral Presentation Australian Society for Microbiology Annual Scientific Meeting 2018

Integrating genomics and transcriptomics to understand Burkholderia pseudomallei evolution in the cystic fibrosis lung (#104)

Erin P. Price 1 2 , Linda T. Viberg 2 , Timothy J. Kidd 3 4 , Scott C. Bell 5 6 , Bart J. Currie 2 7 , Derek S. Sarovich 1 2
  1. Faculty of Science, Health, Education and Engineering, University of the Sunshine Coast, Sippy Downs, QLD, Australia
  2. Global and Tropical Health Division, Menzies School of Health Research, Tiwi, NT, Australia
  3. School of Chemistry and Molecular Biosciences, The University of Queensland, St Lucia, QLD, Australia
  4. Faculty of Medicine, The University of Queensland, Herston, QLD, Australia
  5. Lung Bacteria Laboratory, QIMR Berghofer Medical Research Institute, Herston, QLD, Australia
  6. Department of Thoracic Medicine, The Prince Charles Hospital, Chermside, QLD, Australia
  7. Department of Infectious Diseases and Northern Territory Medical Program, Royal Darwin Hospital, Tiwi, NT, Australia

The melioidosis bacterium, Burkholderia pseudomallei, is increasingly being recognised as a pathogen in patients with cystic fibrosis (CF), with approximately 30 cases documented to date. We first catalogued genome-wide variation of paired, isogenic B. pseudomallei isolates from seven Australasian CF cases, which were collected between four and 55 months apart. Strains showed evolutionary patterns similar to those of other chronic infections, including emergence of antibiotic resistance, genome reduction, and deleterious mutations in genes involved in virulence, metabolism, environmental survival, and cell wall components. We identified the first reported B. pseudomallei hypermutator in patient CF9, which was caused by a defective DNA mismatch repair protein, MutS. Further, we identified both known and novel molecular mechanisms conferring resistance to five clinically important antibiotics for melioidosis treatment. We subsequently extended this investigation by documenting the transcriptomic changes in B. pseudomallei in five cases. Following growth in an artificial CF sputum medium, four of the five paired isolates exhibited significant differential gene expression (DE) that affected between 32 and 792 genes. The greatest number of DE events was observed between patient CF9 strains, consistent with the hypermutator status of the latter strain. Two patient isolates harboured duplications that concomitantly increased expression of the β-lactamase gene penA, and a 35kb deletion in another abolished expression of 29 genes. Convergent DE in the chronically-adapted isolates identified two significantly downregulated and 17 significantly upregulated loci, including the antibiotic resistance-nodulation-division (RND) efflux pump BpeEF-OprC, the quorum-sensing hhqABCDE operon, and a cyanide- and pyocyanin- insensitive cytochrome bd quinol oxidase. These convergent pathoadaptations increase the expression of pathways that may suppress competing bacterial and fungal pathogens and that enhance survival in oxygen-restricted environments, the latter of which renders conventional antibiotics less effective in vivo. Treating chronically-adapted B. pseudomallei infections with antibiotics designed to target anaerobic infections, such as the nitroimidazole class of antibiotics, may significantly improve pathogen eradication attempts by exploiting this Achilles heel. Taken together, our work highlights the exquisite adaptability of microorganisms to long-term persistence in their environment and the ongoing challenges of antibiotic treatment in eradicating pathogens in the CF lung.