| A large number of antibiotic-resistant bacteria still commonly exist in secondary effluents after disinfection. Effluent discharge may cause the spread of antibiotic-resistant bacteria in surface water which poses a great threat to human health. The study on the effect of ultraviolet(UV) disinfection is important to control the health risks caused by antibiotic-resistance bacteria. As typical indicators of water quality, E. coli and fecal coliform bacteria could be used to reflect the microbial contamination in water. In this study, using bacteria culture, antibiotic susceptibility test and molecular biological techniques, the inactivation and antibiotic resistance of E. coli and fecal coliforms by UV disinfection were studied systematically, which provided the scientific basis for the control the spread of antibiotic-resistant bacteria in urban water environment.Selecting the five antibiotic-resistant E. coli strains(SER2, SER6-1, SER6-2, IER6 and IER8) isolated from the municipal wastewater treatment plant and one E. coli strain(ATCC25922) susceptible to antibiotic as the targets, UV disinfection experiments were conducted. It was found that the inactivation rates of the six strains gradually increased with the increased irradiation doses. When the UV doses reached 20 mJ/cm2, the microbial reduction of six strains reached more than 4.40-log. At UV dose of 12 mJ/cm2, the inactivation rates of SER6-1, SER6-2, IER6 and IER8 were significantly lower than that of ATCC25922 strain. The results showed that multi-drug resistant bacteria have higher resistance to UV disinfection at the low radiation doses. After UV treatment of a fluence of 200 mJ/cm2, the surface of E.coli(SER6-1) cells appeared sunken or wrinkled, even damaged. The inactivation rates were not significantly different during UV disinfection when the concentration of suspended particles was 20 mg/L in water samples.The K-B disc agar diffusion method and molecular biology techniques were used to determine the effect of antibiotic resistance of E. coli during UV disinfection. After the UV dose of 80 mJ/cm2, the diameter of inhibition zone of gentamicin(GEN), chloramphenicol(CHL) and norfloxacin(NOR) for E. coli(SER6-1) changed significantly compared with that of before disinfection(p <0.05). Four kinds of tetracycline resistance genes(tet A, tetB, tet M and tetW), two kinds of sulfonamides resistance genes(sul1 and sul2) and three kinds of lactam resistance genes(TEM, CMY 2 and CTX-MU) were detected in the five test strains. UV disinfection could cause the 16 S rDNA and plasmid DNA damage. At the same UV doses, the ARGs damage of SER2 strain was more serious than that of SER6-1 strain. UV disinfection increased the relative abundance of the resistance genes. The growth rate of the relative abundance of sul2 gene was higher than that of tet A and tetB genes in test strains.Secondary effluents after 20 mJ/cm2 UV irridation, the inactivation rate of fecal coliforms reached 3.59-log. UV disinfection increased the different antibiotic resistance rates of fecal coliform in the municipal wastewater treatment plant effluents. At the same UV dose, the inactivation rates of two-drug resistant and three-drug resistant fecal coliforms were lower than that of fecal coliforms, which is probably attributed to the phenomenon of the antibiotic resistant rates obviousincreased after UV disinfection. |
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