组氨酸激酶AgrC在亚抑菌浓度环丙沙星促进金黄色葡萄球菌生物膜形成中的作用机制

Role of histidine kinase AgrC in Staphylococcus aureus biofilm enhancing effects by sub-minimal inhibitory concentration ciprofloxacin

目的探讨组氨酸激酶AgrC在亚抑菌浓度环丙沙星促进金黄色葡萄球菌生物膜形成中的作用机制,为金黄色葡萄球菌生物膜相关感染的治疗提供新的思路。方法于2021年中南大学湘雅三医院检验科收集皮肤组织和体液标本,采用微量肉汤稀释法测定环丙沙星对实验菌株的最低抑菌浓度;采用结晶紫染色法观察不同亚抑菌浓度环丙沙星处理金黄色葡萄球菌后的生物膜形成情况;利用SYTO9和PI荧光染料分析亚抑菌浓度环丙沙星对金黄色葡萄球菌生物膜形成的影响;通过逆转录荧光定量PCR检测亚抑菌浓度环丙沙星对金黄色葡萄球菌agrC基因及其调控基因agrA、icaA和icaR的表达水平的影响;最后,通过等温滴定量热法验证亚抑菌浓度环丙沙星与AgrC蛋白受体的结合作用;数据采用x¯±s表示,服从正态分布和方差齐性则采用方差分析,否则采用非参数检验,以P<0.05为差异有统计学意义。结果药敏试验结果显示环丙沙星对金黄色葡萄球菌的最低抑菌浓度为0.25~0.5 mg/L。亚抑菌浓度的环丙沙星可促进金黄色葡萄球菌生物膜的形成,在1/4倍最低抑菌浓度即可开始出现显著作用[ATCC 43300(t=7.42,P=0.002)、临床菌株SA1(t=5.42,P=0.005)、SA2(t=6.38,P=0.002)、SA3(t=4.8,P=0.009)、SA4(t=7.06,P=0.002)和SA5(t=4.36,P=0.004)]。激光共聚焦显微镜观察发现亚抑菌浓度的环丙沙星可明显促进金黄色葡萄球菌生物膜的形成,增加生物膜的形成量并使生物膜显著聚集成三维立体结构。逆转录荧光定量PCR结果显示,亚抑菌浓度的环丙沙星对agrC基因表达水平无显著影响,但使agrA(t=4.42,P=0.003)和icaR(t=4.49,P=0.007)表达水平下降[(0.61±0.24)和(0.56±0.12)],icaA表达水平升高[1.51±0.19(t=5.24,P=0.009)],差异有统计学意义。等温滴定量热法分析发现,环丙沙星与AgrC蛋白受体具有较好的结合力。结论亚抑菌浓度环丙沙星可能通过结合AgrC蛋白受体,影响下游agrA、icaA和icaR基因表达水平,从而促进生物膜形成,增加金黄色葡萄球菌的抗菌药物耐药性。

Objective To investigate the mechanism of histidine kinase AgrC in Staphylococcusaureus biofilm formation enhancements under a environment with sub-minimal inhibitory concentration(sub-MIC)ciprofloxacin,aiming to shed new light on the antibiotic treatment for S.aureus biofilm-related infections.Methods Clinical isolates were collected from the skin tissue and body fluid samples at the Department of Medicine Clinical Laboratory,the Third Xiangya Hospital of Central South University in 2021.Microdilution broth method was used for determining the minimum inhibitory concentration(MIC).Biofilm assays were performed by using crystal violet staining assay and SYTO9 and PI fluorescent dye staining.Reverse transcription real-time fluorescence quantitative PCR(qRT-PCR)was used to assess the transcriptional levels of the biofilm regulatory genes(agrC,agrA,icaA and icaR)of S.aureus treated with different sub-MIC concentrations of ciprofloxacin.Isothermal titration calorimetry(ITC)was used to analyze the binding affinity of ciprofloxacin to histidine kinase AgrC.The data setwere presented as x¯±s,analysis of variance or nonparametric test is used based on the distribution and homogeneity of variance of the data set.P<0.05 indicates statistically significant differences.Results The MIC of ciprofloxacin against S.aureus was 0.25-0.5 mg/L.Ciprofloxacin could significantly promote the ability of S.aureus biofilm formation at the concentration of 1/4×MIC[ATCC 43300(t=7.42,P=0.002),SA1(t=5.42,P=0.005),SA2(t=6.38,P=0.002),SA3(t=4.8,P=0.009),SA4(t=7.06,P=0.002)and SA5(t=4.36,P=0.004)].The result of fluorescent staining showed that sub-MIC of ciprofloxacin could significantly promote the biofilm formation of S.aureus.The result of qRT-PCR suggested that there was no significant change in agrC gene expression,but the expression level of agrA(t=4.42,P=0.003)and icaR(t=4.49,P=0.007)was significantly decreased in the presence of sub-MIC ciprofloxacin[(0.61±0.24)and(0.56±0.12)],and the expression level of icaA was increased[1.51±0.19(t=5.24,P=0.009)].The result of ITC showed that ciprofloxacin had a significantly high affinity with AgrC.Conclusion Sub-MIC of ciprofloxacin could promote the biofilm formation of S.aureus and increase its antibiotic resistance by binding to the AgrC protein receptor and affecting the expression of agrA,icaA and icaR genes.