Role of histidine kinase AgrC in Staphylococcus aureus biofilm enhancing effects by sub-minimal inhibitory concentration ciprofloxacin / 中华检验医学杂志

ABSTRACT

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 xˉ±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 a grA, icaA and icaR genes.