Antibiotic susceptibility of Pseudomonas aeruginosa biofilm to ulifloxacin and other fluoroquinolones

Abstract number: R2259

Ceccarini P., Capezzone de Joannon A., Rossi V.

Objectives:Pseudomonas aeruginosa is one of the most medically relevant biofilm forming bacterium and an important causative agent of many human infections. Since ulifloxacin, the active form of the prodrug prulifloxacin, is a quinolone with a potent antipseudomonal activity, this study intended to determine in vitro the activity of ulifloxacin compared to other fluoroquinolones (FQs) on P. aeruginosa PAO1 biofilm.

Methods: the activity of ulifloxacin, ciprofloxacin, levofloxacin and moxifloxacin on P. aeruginosa PAO1 was studied both using a polystyrene 96-wells plate biofilm susceptibility assay (MBEC™; Innovotech) and the standard microdilution method (CLSI). Biofilm was formed on the pegs of a modified microtiter lid culturing P. aeruginosa PAO1 in Trypticase Soy Broth for 7–9 h to obtain a bacterial biofilm population from 3×10⁶ to 5×10⁷ colonies forming units (CFU) /peg. Activity of FQs on biofilm was determined after 24 h treatment with drugs (concentrations range from 1 to 512 mg/L) evaluating the bactericidal activity on biofilm disrupted by sonication and measuring bacterial regrowth both in fresh broth medium and on agar plates by CFU determination.

Results: MICs were obtained following the standard microdilution method using as initial inoculum the broth culture which originated biofilm. MICs expressed in mg/L were 0.25 for ulifloxacin, 0.5 for ciprofloxacin, 2 for levofloxacin and 4 for moxifloxacin.

A complete eradication of sessile cells and the minimum biofilm eradication concentration (MBEC) on 7.5 h biofilm (3×10⁶ CFU/peg) was obtained with ulifloxacin at 2 mg/L and at higher concentrations with the other tested FQs.

High killing effect was obtained on older biofilm (9 h and 5×10⁷ CFU/peg) at concentrations of about 4 times MIC values for all FQ. In particular a 5 log reduction was obtained at the following concentrations: 1–2 mg/L of ulifloxacin, 2 mg/L of ciprofloxacin, 4–8 mg/L of levofloxacin and 8–16 mg/L of moxifloxacin.

Conclusions: FQ antibiotics exerted a remarkable bactericidal activity against P. aeruginosa PAO1 biofilm. In particular ulifloxacin showed the highest activity at concentrations equivalent to those found in plasma and tissues after oral treatment.