Oral Presentation Australian Society for Microbiology Annual Scientific Meeting 2022

The efficacy of antioxidant-antibiotic combination therapy on Achromobacter xylosoxidans in a cystic fibrosis lung cell model. (82148)

Aditi Aiyer 1 , Greg Whiteley 2 , Trevor Glasbey 2 , Erik Kriel 2 , Jessica Farrell 1 2 , Jim Manos 1 , Theerthankar Das Ashish Kumar 1
  1. University of Sydney, Sydney, NSW, Australia
  2. Whiteley Corporation, , Level 5, 12 Mount Street North Sydney, Sydney, NSW 2060, Australia

Background: Cystic fibrosis (CF) is a genetic disorder causing dysfunctional ion transport resulting in accumulation of viscous mucus that fosters chronic bacterial biofilm-associated infection in the airways. Achromobacter xylosoxidans is an increasingly prevalent CF pathogen associated with lung disease in CF [1]. Current research lacks an understanding of effective treatment options for chronic Achromobacter spp. infection of human lung [2].

Aim: To investigate the synergistic or additive effect of an antioxidant-antibiotic combination therapy (CT) on A. xylosoxidans in an artificial sputum (ASMDM)+BEAS-2B bronchial epithelial cell model for CF infection.

Methods: This study investigates synergy between the commonly used CF antibiotics ciprofloxacin (0.5–128 µg/mL) and colistin (0.5–128 µg/mL) when combined with the antioxidant N-acetylcysteine at neutralised pH (NACneutral) (0.5–16.3 mg/mL) against three Achromobacter sp. strains grown as planktonic and biofilm cultures [3]. Potential synergism was screened for using checkerboard assays, from which fractional inhibitory concentration indices (FICI) were calculated. Synergistic (FICI ≤ 0.5) and additive (0.5 > FICI ≥ 1) combinations were tested on 48 h old mature biofilms and using invasion assays. Results for colony forming units (CFU/mL) were derived from growth in an ASMDM+BEAS-2B model; created by adding 20% ASMDM to Dulbecco’s-Modified-Eagle-Medium (DMEM).

Results: We found evidence of synergy between NACneutral, ciprofloxacin and colistin in FICI analysis in planktonic culture, but these results were not corroborated in biofilm-based testing. While many combinations did not correlate with FICI analysis, CFU/mL reductions of log10 1-2 were still observed in clinical isolates compared to controls in the ASMDM+BEAS-2B cell model.

Conclusions: Our findings suggest that while planktonic FICI analysis may not directly translate to biofilm growth, the combinations investigated were still able to significantly reduce bacterial loads in the BEAS2B-artificial sputum model compared to the components alone and positive controls. Future directions include refining synergy testing to function in biofilms and determine the detailed mechanism of action of NAC to better predict synergy in other pathogenic species.

  1. De Baets, F.; Schelstraete, P.; Van Daele, S.; Haerynck, F.; Vaneechoutte, M. Achromobacter xylosoxidans in cystic fibrosis: prevalence and clinical relevance. J Cyst Fibros 2007, 6, 75-78, doi:10.1016/j.jcf.2006.05.011.
  2. Firmida, M.C.; Pereira, R.H.; Silva, E.A.; Marques, E.A.; Lopes, A.J. Clinical impact of Achromobacter xylosoxidans colonization/infection in patients with cystic fibrosis. Braz J Med Biol Res 2016, 49, e5097, doi:10.1590/1414-431X20155097.
  3. Aiyer, A.; Visser, S.K.; Bye, P.; Britton, W.J.; Whiteley, G.S.; Glasbey, T.; Kriel, F.H.; Farrell, J.; Das, T.; Manos, J. Effect of N-Acetylcysteine in Combination with Antibiotics on the Biofilms of Three Cystic Fibrosis Pathogens of Emerging Importance. Antibiotics (Basel) 2021, 10, doi:10.3390/antibiotics10101176.