Oral Presentation Australian Society for Microbiology Annual Scientific Meeting 2024

Pseudomonas aeruginosa biofilm growth kinetics and dispersal responses to sodium nitroprusside (104551)

Xavier Bertran i Forga 1 2 , Jilong Qin 1 2 , Kathryn E. Fairfull-Smith 1 2 3 4 , Makrina Totsika 1 2
  1. Queensland University of Technology, South Brisbane, QLD, Australia
  2. Max Planck Queensland Centre, Queensland University of Technology, South Brisbane, Qld, Australia
  3. School of Chemistry and Physics, Queensland University of Technology, South Brisbane, Qld, Australia
  4. Centre for Materials Science, Queensland University of Technology, South Brisbane, Qld, Australia

Sodium nitroprusside (SNP) is a NO donor widely used to induce dispersal in biofilms of the major agent of chronic infections P. aeruginosa. Biofilm dispersal agents such as nitric oxide (NO) are reported to enhance antimicrobial activity against biofilm infections by reverting biofilm bacteria to their planktonic growth state, in which they lose biofilm-associated antimicrobial tolerance. However, SNP-mediated dispersal has only been consistently observed in flow-cell culture systems. In contrast, biofilms grown in microtiter plate systems, which are preferred for in vitro testing, yield inconsistent results for SNP treatment. Studies report from biofilm decreases to increases in biofilm and planktonic biomass after 24h of treatmentAdditionally, studies exploring NO-mediated biofilm dispersal in P. aeruginosa may differ in NO-donor concentration, duration of treatment and culture conditions, thus hindering comparisons across findings.

Here we explore the activity of SNP on established P. aeruginosa biofilms, as well as on biofilm growth kinetics and planktonic cell growth to understand its potential as a biofilm dispersal agent. In microtiter plates, 4h-old biofilms grown in minimal media increased in biomass when treated either with SNP or FeSO4 for 30 minutes. Due to iron promoting attachment of planktonic cells, the increased biofilm biomass associated to SNP exposure suggested that the iron centre of the molecule could be playing an important role in biofilm formation. Also, planktonic cultures exhibited increased cell densities when grown with SNP or FeSO4. To determine whether the iron in SNP was responsible for the increases in biofilm biomass, we eliminated any traces of iron from our culture media by pre-treating it with 2,2’-bipyridine. While bacterial growth was inhibited in these conditions, growth could be rescued by the addition of FeSO4 or SNP.

Our work revealed no detectable dispersal is triggered by subinhibitory concentrations of SNP in P. aeruginosa biofilms grown in microtiter plates. The compound instead promotes biofilm and planktonic growth due to its iron being utilised by bacteria. Thus, our results suggest that future studies investigating the molecular mechanisms of NO-mediated dispersal utilise validated NO donors such as N-diazeniumdiolates to avoid undesired iron-related effects.