Department of Biotechnology, Alagappa University, Karaikudi, India.
Indian J Med Res. 2013 May;137(5):963-71.
BACKGROUND & OBJECTIVES: Subinhibitory concentrations (sub-MICs) of antibiotics, although not able to kill bacteria, but influence bacterial virulence significantly. Fluoroquinolones (FQs) which are used against other bacterial pathogens creates resistance in non-targeted Streptococcus pyogenes. This study was undertaken to characterize the effect of sub-MICs of FQs on S. pyogenes biofilm formation.
Biofilm forming six M serotypes M56, st38, M89, M65, M100 and M74 of S. pyogenes clinical isolates were challenged against four FQs namely, ciprofloxacin, ofloxacin, levofloxacin and norfloxacin. The antibiofilm potential of these FQs was analysed at their subinhibitory concentrations (1/2 to 1/64 MIC) using biofilm assay, XTT reduction assay, scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM).
Among the four FQs tested, ofloxacin and levofloxacin at 1/2 MIC showed the maximum inhibition (92%) of biofilm formation against M56 and M74 serotypes. FQs effectively interfered in the microcolony formation of S. pyogenes isolates at 1/2 to 1/8 sub-MICs. Inhibition of biofilm formation was greatly reduced beyond 1/16 MICs and allowed biofilm formation. XTT reduction assay revealed the increase in metabolic activity of S. pyogenes biofilm against the decrease in FQs concentration. SEM and CLSM validated the potential of sub-MICs of FQs against the six S. pyogenes.
INTERPRETATION & CONCLUSIONS: Our results showed that the inhibitory effect all four FQs on S. pyogenes biofilm formation was concentration dependent. FQs at proper dosage can be effective against S. pyogenes and lower concentrations may allow the bacteria to form barriers against the antibiotic in the form of biofilm.
尽管亚抑菌浓度（sub-MIC）的抗生素不能杀死细菌，但它们会显著影响细菌的毒力。用于对抗其他细菌病原体的氟喹诺酮类药物（FQs）会使非靶向性酿脓链球菌产生耐药性。本研究旨在研究 FQs 的亚抑菌浓度对酿脓链球菌生物膜形成的影响。
用四种 FQs（环丙沙星、氧氟沙星、左氧氟沙星和诺氟沙星）对酿脓链球菌临床分离株的六个 M 血清型（M56、st38、M89、M65、M100 和 M74）进行亚抑菌浓度（MIC 的 1/2 至 1/64）的生物膜形成挑战。使用生物膜测定法、XTT 还原测定法、扫描电子显微镜（SEM）和共聚焦激光扫描显微镜（CLSM）分析这些 FQs 的抗生物膜潜力。
在测试的四种 FQs 中，氧氟沙星和左氧氟沙星在 1/2 MIC 时对 M56 和 M74 血清型表现出最大的生物膜形成抑制作用（92%）。FQs 在 1/2 至 1/8 亚 MIC 时有效地干扰酿脓链球菌分离株的微菌落形成。超过 1/16 MIC 时，生物膜形成的抑制作用大大降低，并允许生物膜形成。XTT 还原测定法显示，随着 FQs 浓度的降低，酿脓链球菌生物膜的代谢活性增加。SEM 和 CLSM 验证了 FQs 亚 MIC 对六种酿脓链球菌的潜力。
我们的结果表明，四种 FQs 对酿脓链球菌生物膜形成的抑制作用均呈浓度依赖性。适当剂量的 FQs 可有效对抗酿脓链球菌，而较低浓度可能使细菌形成生物膜形式的抗生素屏障。
