Effect of subinhibitory doses of rifaximin on in vitro Pseudomonas aeruginosa adherence and biofilm formation to biotic and abiotic surface models.

Background: The adhesion of Pseudomonas aeruginosa to biotic and abiotic surfaces is responsible for the persistence and development of bacterial infection.

Objectives: To fill the gap in the knowledge regarding the relationship between rifaximin susceptibility and biofilm formation, and to investigate the effect of subinhibitory doses of rifaximin on the adhesion and biofilm formation.

Material and methods: A total of 10 isolates of P. aeruginosa were obtained from 110 urine samples of urinary tract infection (UTI) patients. Biofilm formation on polystyrene microtiter plates, minimum inhibitory concentrations (MICs) of rifaximin against the 10 isolates of P. aeruginosa (Pa1-Pa10), the effect of sub-MICs of rifaximin (0.5 × MIC, 0.25 × MIC, 0.125 × MIC, and 0.06 × MIC) on biofilm formation by the Pa4 isolate to polystyrene microtiter plates, and the adhesion to human epithelial cells (HECs) in vitro were evaluated.

Results: The MICs of rifaximin against 10 isolates ranged from 62.5 μg/mL to 1000 μg/mL. The Pa4 isolate produced the highest level of biofilm formation, while the MIC of Pa4 was 125 μg/mL. There was no correlation between bacterial susceptibility to rifaximin and biofilm formation (r: -0.016; p > 0.05). Sub-MIC doses of rifaximin significantly reduced the biofilm formation on abiotic surfaces, while only 0.5 × MIC, 0.25 × MIC and 0.12 × MIC of rifaximin reduced the adhesion to HECs significantly (p < 0.05) in a dose-dependent manner.

Conclusions: This pioneering study demonstrated the negative effect of sub-MIC doses of rifaximin on biofilm formation and adhesion to abiotic and biotic surfaces in vitro.