1. Antimicrob Agents Chemother. 2020 Mar 24;64(4):e02204-19. doi: 
10.1128/AAC.02204-19. Print 2020 Mar 24.

Activity of Antibiotics against Pseudomonas aeruginosa in an In Vitro Model of 
Biofilms in the Context of Cystic Fibrosis: Influence of the Culture Medium.

Diaz Iglesias Y(1), Van Bambeke F(2).

Author information:
(1)Pharmacologie cellulaire et moléculaire; Louvain Drug Research Institute, 
Université catholique de Louvain (UCLouvain), Brussels, Belgium.
(2)Pharmacologie cellulaire et moléculaire; Louvain Drug Research Institute, 
Université catholique de Louvain (UCLouvain), Brussels, Belgium 
francoise.vanbambeke@uclouvain.be.

Pseudomonas aeruginosa is a major cause of respiratory biofilm-related 
infections in patients with cystic fibrosis. We developed an in vitro 
pharmacodynamic model to study the activity of antipseudomonal antibiotics 
against PAO1 biofilms grown in artificial sputum medium with agar [ASM(+)] 
versus that against biofilms grown in Trypticase soy broth supplemented with 
glucose and NaCl (TGN). We measured bacterial counts, metabolic activity 
(fluorescein diacetate [FDA] hydrolysis), and biomass (crystal violet 
absorbance). Biofilms grew slower in ASM(+) than in TGN but reached the same CFU 
counts and metabolic activity in both media and a slightly higher biomass after 
48 h in ASM(+) than in TGN. The concentration-response curves of the antibiotics 
after 24 h of incubation with mature biofilms showed maximal effects ranging 
from a 3 (ciprofloxacin)- to a 1.5 (ceftazidime, meropenem)-log10-CFU decrease, 
with tobramycin and colistin showing intermediate values. These maximal 
reductions in the numbers of CFU were similar in both media for ciprofloxacin 
and β-lactams but lower in ASM(+) than in TGN for tobramycin and colistin; they 
were reached at concentrations lower than the human maximum concentration in 
plasma for ciprofloxacin and β-lactams only. The reductions in metabolic 
activity and in biomass were low in both media. Small-colony variants were 
selected by tobramycin in ASM(+) and by ciprofloxacin in both media. The model 
was then successfully applied to 4 isolates from patients with cystic fibrosis. 
These biofilms showed CFU counts similar to those of PAO1 biofilms in ASM(+) but 
a higher biomass than PAO1 biofilms in ASM(+) and moderate differences in their 
susceptibility to antibiotics from that of PAO1 biofilms grown in this medium. 
This model proved useful to establish the pharmacodynamic profile of drugs 
against P. aeruginosa biofilms in the context of cystic fibrosis.

Copyright © 2020 American Society for Microbiology.

DOI: 10.1128/AAC.02204-19
PMCID: PMC7179293
PMID: 32015047