Effects of subinhibitory concentrations (sub-MICs) (1/4, 1/8, 1/16 or 1/32 of the MICs) of four quinolone antibiotics on surface hydrophobicity of two Acinetobacter baumannii strains (R1 and R2) were tested. Hydrophobicity was evaluated by adherence of bacteria to xylene and their aggregation in ammonium sulphate solutions. Norfloxacin in concentrations of 1/4 or 1/8 of the MIC decreased hydrophobicity of R1 strain and of R2 strain in concentration of 1/16 of the MIC. Ciprofloxacin was efficient for both strains mainly in concentration of 1/4 of their MICs. Enoxacin (1/8 MIC) more effectively reduced hydrophobic properties only in R2 strain. The other concentrations of the above-mentioned antibiotics as well as all tested concentrations of pefloxacin pract ically did not affect bacterial surface hydrophobicity.

        Key words: quinolones – subinhibitory concentrations – Acinetobacter baumannii – surface hydrophobicity