Sensitivity to the serum bactericidal activity and surface hydrophobicity of Acinetobacter bauman- nii strains isolated from the urinary (UT) or respiratory tract (RT) of patients after exposure to imipenem at subinhibitory concentrations (sub-MICs) (1/4, 1/8 or 1/16 of their MICs) were tested. The antibiotic at the mentioned concentrations decreased significantly the sensitivity of strain UT to the bactericidal activity of human serum. Sensitivity to the bactericidal activity of serum of strain RT was affected only very ineffectively. Imipenem at 1/4 of their MICs reduced the cell surface hydrophobicity to 76.1% (strain UT) and to 81.9% (strain RT) compared with control values (without imipenem). Lower concentrations of antibiotic influenced cell surface hydrophobicity only to a smaller extent. Possible decrease in sensitivity of bacteria to the bactericidal activity of serum after treatment with imipenem in „in vivo“ experiments would manifest an increase in virulence of these strains.

        Key words: Acinetobacter baumannii – sensitivity to bactericidal activity of serum – surface hydrophobicity – imipenem – subinhibitory concentrations.