[Study on the transfer mechanism and destructive law of the bacterial antibiotic resistance genes disinfected by chlorination]

Objective: To study the response of Escherichia coli (E. coli) HB101 (plasmid pUC19) and its carried antibiotic resistance genes to the process of cholorination under different environmental conditions. Methods: The E. coli strain was reacted with sodium hypochlorite at the concentration of 0.5, 0.75, 1.00, and 0.55 mg/L, then the residual chlorine and the colonies were detected at the 0.25, 1, 2, 5, 10, 20, and 30 min of the reaction, respectively. The first order disinfection kinetic model and EFH model were used to evaluate the inactivation effect of E. coli (plasmid pUC19) treated by sodium hypochlorite, while the plasmid pUC19 and antibiotic resistance gene amp(r) were detected by PCR method. Besides, the logarithm of Ct (residual chlorine in t) under different concentration were calculated. Results: The temperature and pH value played important roles on the inactivation of E. coli and elimination of plasmid pUC19 and amp(r) under the function of sodium hypochlorite. The Ct value needed for 5-log of E.coli HB101(pUC19) inactivation at 4, 20, 36 ℃ was 11.92, 10.28, 7.67, respectively, and when the pH was in 6.0, 7.0, 8.0, with chloride concentration were 0.75, 0.70, 0.55 mg/L, the Ct value needed for reached to 6.68, 10.28, 15.73 min·mg/L. At pH 7.2 condition, when the temperature was 4, 20, 36 ℃, and chloride concentration were 9, 5, 3 mg/L.The required Ct values to completely destroy the transformation function of free antibiotic resistant plasmids were 36.11, 34.17,16.09 min·mg/L. Sodium hypochlorite disinfection can release free ampr gene and even the transformed plasmid pUC19, and pollute the water body. Only when the Ct value reached 903.03 min·mg/L, the complete ampr gene can be destroyed which was far more exceed the bacterial lethal Ct value. Conclusion: Even if all the antibiotic resistant bacteria were inactivated, the antibiotic resistant plasmids or genes might still maintain complete with the transformable function, which may result in new potential risks of waterborne diseases.