Ciprofloxacin-Induced Antibacterial Activity Is Atteneuated by Pretreatment with Antioxidant Agents

Abstract

Ciprofloxacin works through interfering with replication and transcription of bacterial DNA, which leads to increased oxidative stress, and death of bacterial cells. Drugs with strong antioxidant such as tempol, melatonin and pentoxifylline might interfere with the antibacterial activity of ciprofloxacin. In the current study, the effect of these drugs on the cytotoxicity of ciprofloxacin was investigated against several reference bacteria. Standard bacterial strains included Escherichia coli ATCC 35218, Staphylococcus aureus ATCC29213, Pseudomonas aeruginosa ATCC 9027, Staphylococcus epidermidis ATCC 12228, Acinetobacter baumannii ATCC 17978, Proteus mirabilis ATCC 12459, Klebsiella pneumoniae ATCC 13883, methicillin-resistant Staphylococcus aureus (MRSA) (ATCC 43300), and Streptococcus pneumoniae (ATCC 25923). The antibacterial activity of ciprofloxacin with or without treatment of bacterial cells by tempol, melatonin or pentoxifylline was assessed using the disc diffusion method and by measuring the minimum inhibitory concentration (MIC) and zones of inhibition of bacterial growth. All of the tested bacterial strains were sensitive to ciprofloxacin. When treated with tempol, melatonin or pentoxifylline, all bacterial strains showed significantly smaller zones of inhibition and larger MIC values compared ciprofloxacin alone. In correlation, reactive oxygen species (ROS) generation induced by ciprofloxacin antibacterial action was diminished by treatment of bacterial cells with tempol, melatonin or pentoxifylline. In conclusion, results indicate the possible antagonistic properties for agents with antioxidant properties such as tempol, melatonin and pentoxifylline when they are used concurrently with flouroquinolones. This could be related to the ability of these agents to inhibit oxidative stress in bacterial cells.

Keywords: MIC; antimicrobial susceptibility; ciprofloxacin; melatonin; pentoxifylline; tempol.

Figure 1

Ciprofloxacin-induced antibacterial action on E. coli cells is preceded by a time-dependent reactive oxygen species (ROS) generation. Figure 1 (A): Mean fluorescence intensity (MFI) was shown as the ratio of geometric mean fluorescence intensity of the test sample and the corresponding control. The data shown are representative of three individual experiments. Figure 1 (B): Pretreatment for 16 hour of E. coli cells with tempol, melatonin or pentoxifylline (100 µM) inhibited ciprofloxacin-induced ROS generation. 2’,7’-dichlorofluorescein diacetate (DCF-DA) (10 µM) was added for the last 30 minutes of incubation. The intensity of DCF-DA fluorescence was determined using flowcytometry with an excitation wavelength of 480 nm and an emission wavelength of 530 nm. The data shown are representative of three individual experiments. * indicates significant difference from the control, and ciprofloxacin only treated groups (One way ANOVA followed by Tukey’s post-hoc test, p < 0.05 in each case).