title: [Aminoglycosides and colistin inhibit biofilm formation in Klebsiella pneumoniae].
abstract: OBJECTIVE
  To evaluate the effect of subinhibitory concentrations (sub-MICs) of amikacin, tobramycin and colistin on biofilm formation, surface hydrophobicity, lipase activity and response to oxidative stress in two clinical K. pneumoniae strains.
  
  
  METHODS
  Biofilm formation was quantitatively determined by a crystal violet absorption assay, surface hydrophobicity was measured by adherence of bacteria to xylene, lipase activity was determined by the spectrophotometric method with Tween-20 as a substrate and oxidative stress was visualized as a zone of clearing around the disc soaked with hydrogen peroxide.
  
  
  RESULTS
  The antibiotics significantly reduced bacterial biofilm formation in a dose-dependent manner. They were most effective at concentrations of 1/2 and 1/4 MIC. Biofilm formation was inhibited by 1/2 MICs of amikacin to 21.2% (strain 39) and 22.6% (61/P), of tobramycin to 25.1% (39) and 19.5% (61/P) and of colistin to 7.4% (39) and 19.1% (61/P) of the control values (no antibiotic). Similarly, 1/4 MICs reduced biofilm formation to 28.6% (39) and 28.9% (61/P) of the control levels for amikacin, to 35.3% (39) and 20.5% (61/P) for tobramycin and to 8.7% (39) and 20.4% (61/P) for colistin. Cultivation of the strains with the antibiotics at 1/16 MICs was least effective in inhibiting biofilm formation. It was reduced to 80.4% (39) and 97.7% (61/P) of the control levels for amikacin, to 69.4% (39) and 64.4% (61/P) for tobramycin and to 61.3% (39) and 74.7% (61/P) for colistin. The tested strains were strongly hydrophilic and changes in surface hydrophobicity caused by antibiotics were negligible. Most antibiotic treated strains showed mildly increased sensitivity to oxidative stress and decreased lipase activity (with the exception of colistin in strain 39).
  
  
  CONCLUSIONS
  Amikacin, tobramycin and colistin at sub-MICs considerably reduced biofilm formation K. pneumoniae strains, in most mildly increased sensitivity to oxidative stress, decreased lipase activity but practically did not affect adherence to xylene.
authors.affiliation: Slovenská zdravotnícka univerzita, Bratislava. anna.hostacka@szu.sk
authors.forename: A
authors.initials: A
authors.lastname: Hostacká
authors.forename: I
authors.initials: I
authors.lastname: Ciznár