UV light tolerance and reactivation potential of tetracycline-resistant bacteria from secondary effluents of a wastewater treatment plant

Tetracycline-resistant bacteria(TRB) are of concern as emerging microbial contaminants in reclaimed water.To understand the effects of UV disinfection on TRB,both inactivation and reactivation profiles of TRB,as well as 16 tetracycline-resistant isolates from secondary effluent,were characterized in this study.The inactivation ratio of TRB was significantly lower(3.0-log) than that of heterotrophic bacteria(>4.0-log) in the secondary effluent.Additionally,the proportion of TRB significantly increased from 1.65%to 15.51%under20 mJ/cm2ultraviolet(UV) exposure.The inactivation rates of tetracycline-resistant isolates ranged from 0.57/s to 1.04/s,of which tetracycline-resistant Enterobacter-1 was the most tolerant to UV light.The reactivation of TRB,tetracycline-resistant isolated strains,as well as heterotrophic bacteria commonly occurred in the secondary effluent even after20 mJ/cm2UV exposure.The colony forming ability of TRB and heterotrophic bacteria reached 3.2-log and 3.0-log under 20 mJ/cm2UV exposure after 22 hr incubation.The final inactivation ratio of tetracycline-resistant Enterobacter-1 was 1.18-log under 20 mJ/cm2UV exposure after 22 hr incubation,which is similar to those of TRB(1.18-log) and heterotrophic bacteria(1.19-log).The increased proportion of TRB and the reactivation of tetracycline-resistant enterobacteria in reclaimed water could induce a microbial health risk during wastewater reuse.