Homogentisate 1-2-Dioxygenase Downregulation in the Chronic Persistence of Pseudomonas aeruginosa Australian Epidemic Strain-1 in the CF Lung.

Christopher J Harmer,Matthew Wynn,Stuart Cordwell,Jim Manos,Barbara R Rose,Rachel Pinto,James A Triccas,Colin Harbour

doi:10.1371/journal.pone.0134229

Christopher J Harmer, Matthew Wynn + Show 6 more

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https://doi.org/10.1371/journal.pone.0134229

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Journal: PloS one	Publication Date: Aug 7, 2015
Citations: 7	License type: CC BY 4.0

Affiliation: University of Sydney

Abstract

Some Pseudomonas aeruginosa strains including Australian Epidemic Strain-1 (AES-1 or AUS-01) cause persistent chronic infection in cystic fibrosis (CF) patients, with greater morbidity and mortality. Factors conferring persistence are largely unknown. Previously we analysed the transcriptomes of AES-1 grown in Luria broth, nematode growth medium for Caenorhabditis elegans assay (both aerobic) and artificial sputum medium (mainly hypoxic). Transcriptional comparisons included chronic AES-1 strains against PAO1 and acute AES-1 (AES-1R) against its chronic isogen (AES-1M), isolated 10.5 years apart from a CF patient and not eradicated in the meantime. Prominent amongst genes downregulated in AES-1M in all comparisons was homogentisate-1-2-dioxygenase (hmgA); an oxygen-dependent gene known to be mutationally deactivated in many chronic infection strains of P. aeruginosa. To investigate if hmgA downregulation and deactivation gave similar virulence persistence profiles, a hmgA mutant made in UCBPP-PA14 utilising RedS-recombinase and AES-1M were assessed in the C. elegans virulence assay, and the C57BL/6 mouse for pulmonary colonisation and TNF-α response. In C. elegans, hmgA deactivation resulted in significantly increased PA14 virulence while hmgA downregulation reduced AES-1M virulence. AES-1M was significantly more persistent in mouse lung and showed a significant increase in TNF-α (p<0.0001), sustained even with no detectable bacteria. PA14ΔhmgA did not show increased TNF-α. This study suggests that hmgA may have a role in P. aeruginosa persistence in chronic infection and the results provide a starting point for clarifying the role of hmgA in chronic AES-1.

Highlights

Persistent P. aeruginosa infections are the leading cause of morbidity and mortality in cystic fibrosis patients
Previous reports suggest that mutational deactivation of hmgA and pyomelanin overexpression is associated with chronic P. aeruginosa strains infecting cystic fibrosis (CF) patients [17], chronic infection isolates of AES-1 still express hmgA (Table 1) and no pyomelanin, indicating putative regulatory control of hmgA in chronic P. aeruginosa AES-1 to suit the host environment rather than adaptive mutation
AES-1M exhibited greater anaerobic growth compared to AES-1R in ASMDM [10], penetrating into the media with deeper projections by 72 hrs post inoculation, supporting the idea that a consequence of hmgA repression may be an increased ability to thrive in a microaerobic/hypoxic environment, and persist better [26]

Summary

Introduction

Persistent P. aeruginosa infections are the leading cause of morbidity and mortality in cystic fibrosis patients. We compared acute and chronic isogens (AES-1R and AES-1M, respectively) from the same patient taken 10.5 years apart and not eradicated in the interim [9]. HmgA was prominent amongst genes downregulated between acute (AES-1R) and chronic (AES-1M) isogens of AES-1 from the same patient taken 10.5 years apart and not eradicated in the interim (-7.2×, p = 0.03) (Table 1) [9]. In this case, genes were identified using a non-redundant array (PANarray) and growth in a medium that closely mimics cystic fibrosis lung sputum (ASMDM) [10]

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