Reversal of heavy metal-induced antibiotic resistance by dandelion root extracts and taraxasterol

Introduction. Metal exposure is an important factor for inducing antibiotic resistance in bacteria. Dandelion extracts have been used for centuries in traditional Chinese and Native American medicine. Aim. We assessed the effects of dandelion water extracts and taraxasterol on heavy metal-induced antibiotic resistance in Escherichia coli as well as the underlying mechanisms. Methodology. Dandelion extracts were obtained through 4 h of boiling in distilled water. Bacterial growth was monitored with a spectrophotometer. Biochemical assays were performed to assess the activities and gene transcriptions of beta-lactamase and acetyltransferase. Oxidative stress was determined using an oxidation-sensitive probe, H(2)DCFDA. Results. The present study demonstrated that higher concentrations of nickel (>5 mu g ml(-1)), cadmium (>0.1 mu g ml(-1)), arsenic (>0.1 mu g ml(-1)) and copper (>5 mu g ml(-1)) significantly inhibited the growth of E. coli. Lower concentrations of nickel (0.5 mu g ml(-1)), cadmium (0.05 mu g ml(-1)) and arsenic (0.05 mu g ml(-1)) had no effect on bacterial growth, but helped the bacteria become resistant to two antibiotics, kanamycin and ampicillin. The addition of dandelion root extracts and taraxasterol significantly reversed the antibiotic resistance induced by these heavy metals. The supplements of antibiotics and cadmium generated synergistic effects on the activities of beta-lactamase and acetyltransferase (two antibiotic resistance-related proteins), which were significantly blocked by either dandelion root extract or taraxasterol. In contrast, oxidative stress was not involved in the preventative roles of dandelion root extracts and taraxasterol in heavy metal-induced antibiotic resistance. Conclusion. This study suggests that heavy metals induce bacterial antibiotic resistance and dandelion root extracts and taraxasterol could be used to help reverse bacterial resistance to antibiotics.