Vyhodnotenie účinku subinhibičných koncentrácií (sub-MICs) amikacínu, tobramycínu a kolistínu na tvorbu biofilmu, na povrchovú hydrofobicitu, lipázu a odpoveď na oxidačný stres u dvoch klinických kmeňov K. pneumoniae. Metodika: Tvorbu biofilmu sme kvantitatívne vyhodnotili testom absorpcie kryštálovej violete, povrchovú hydrofobicitu adherenciou na xylén, lipázu spektrofotometrickou metódou s Tweenom 20 ako substrátom, oxidačný stres ako zónu vyčírenia obklopujúcu disk nasiaknutý peroxidom vodíka. Výsledky: Antibiotiká výrazne znížili tvorbu bakteriálneho biofilmu v priamej závislosti na koncentrácii. Najúčinnejšie boli v koncentráciách 1/2 a 1/4 MICs. Biofilm po účinku 1/2 sub-MICs amikacínu bol inhibovaný na 21,2 % (kmeň 39) a 22,6 % (kmeň 61/P), po tobramycíne na 25,1 % (39) a 19,5 % (61/P), po kolistíne na 7,4 % (39) a 19,1 % (61/P) kontrolných hodnôt (bez antibiotika). Podobne 1/4 MICs amikacínu zredukovala produkciu biofilmu na 28,6 % (39) a 28,9 % (61/P), tobramycínu na 35,3 % (39) a 20,5 % (61/P) a kolistínu na 8,7 % (39) a 20,4 % (61/P) kontrolných hladín. Biofilm bol najmenej redukovaný po kultivácii kmeňov s 1/16 MICs antibiotík. V týchto prípadoch jeho hodnota bola znížená na 80,4 % (39) a 97,7 % (61/P) kontrolných hodnôt po amikacíne, na 69,4 % (39) a 64,4 % (61/P) po tobramycíne, na 61,3 % (39) a 74,7 % (61/P) po kolistíne. Testované kmene boli silne hydrofilné a zmeny v povrchovej hydrofobicite účinkom antibiotík boli veľmi nepatrné. Kmene po pôsobení antibiotík vo väčšine prípadov vykazovali mierne zvýšenú citlivosť na oxidačný stres a zníženú aktivitu lipázy (s výnimkou kolistínu u kmeňa 39). Záver: Amikacín, tobramycín a kolistín v sub-MICs u kmeňov K. pneumoniae výrazne znížili tvorbu biofilmu, vo väčšine prípadov mierne zvýšili citlivost na oxidačný stres, znížili aktivitu lipázy ale adherenciu na xylén prakticky neovplyvnili.

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). CONCLUSION: 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.

Slovenská zdravotnícka univerzita Bratislava

Aminoglycosides and colistin inhibit biofilm formation in Klebsiella pneumoniae

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