Butucel Eugenia, Balta Igori, McCleery David, Popescu Cosmin Alin, Iancu Tiberiu, Pet Ioan, Marcu Adela, Horablaga Nicolae-Marinel, Stef Lavinia, Corcionivoschi Nicolae
Bacteriology Branch, Veterinary Sciences Division, Agri-Food and Biosciences Institute, Belfast BT4 3SD, UK.
Faculty of Bioengineering of Animal Resources, University of Life Sciences King Mihai I from Timisoara, 300645 Timisoara, Romania.
Antioxidants (Basel). 2022 Nov 4;11(11):2186. doi: 10.3390/antiox11112186.
is responsible for causing Legionnaires' disease and Pontiac fever, also known as legionellosis. The aim of this study was to investigate the mechanistic effect of a mixture of natural antimicrobials (Citrox BCL) in preventing biofilm formation and reducing its in vitro virulence. The minimum inhibitory concentrations were detected at 0.06%, and the MBC was established at 0.125%. Based on the growth curve profile, the sub-inhibitory concentration of 0.02% was further used to study the mechanistic implications in the absence of a cytotoxic effect on A549 cells. At 24 h post-infection, Citrox BCL reduced ( = 0.005) the intracellular growth of when the A549 cells or the bacteria were pre-treated with 0.02% Citrox BCL. This result was replicated when Citrox BCL was added during the 24 h infection assay leading to a reduction in intracellular growth ( = 0.003). Herein we show that at the sub-inhibitory concentration of 0.02%, Citrox CBL lowers the ROS levels in infected A549 cells and causes a 45% reduction in EPS production, a reduction associated with the decline in biofilm formation. Overall, our results corroborate the low c-di-GMP production with the decrease in biofilm formation and low EPS levels. The low EPS levels seemed to be caused by the downregulation of the B and C gene expressions. Moreover, inhibition of A and B gene expressions, leading to lower siderophore levels, suggests that Citrox BCL reduces the ability of to sequester iron and reduce biofilm formation through iron starvation.
负责引起军团病和庞蒂亚克热，也称为军团菌病。本研究的目的是调查天然抗菌剂混合物（Citrox BCL）在预防生物膜形成和降低其体外毒力方面的作用机制。最低抑菌浓度在0.06%时检测到，最低杀菌浓度确定为0.125%。根据生长曲线概况，进一步使用0.02%的亚抑菌浓度来研究在对A549细胞无细胞毒性作用的情况下的作用机制。感染后24小时，当A549细胞或细菌用0.02%的Citrox BCL预处理时，Citrox BCL降低了（P = 0.005）嗜肺军团菌的细胞内生长。当在24小时感染试验期间添加Citrox BCL时，该结果得到重复，导致细胞内生长减少（P = 0.003）。在此我们表明，在0.02%的亚抑菌浓度下，Citrox CBL降低了感染的A549细胞中的活性氧水平，并使嗜肺军团菌胞外多糖产量降低了45%，这种降低与生物膜形成的减少有关。总体而言，我们的结果证实了低环二鸟苷酸产生与生物膜形成减少和低胞外多糖水平之间的关系。低胞外多糖水平似乎是由B和C基因表达的下调引起的。此外，对A和B基因表达的抑制导致铁载体水平降低，这表明Citrox BCL通过铁饥饿降低了嗜肺军团菌螯合铁的能力并减少了生物膜形成。
