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/cm~2 ultraviolet（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/cm~2 UV exposure.The colony forming ability of TRB and heterotrophic bacteria reached 3.2-log and 3.0-log under 20 mJ/cm~2 UV exposure after 22 hr incubation.The final inactivation ratio of tetracycline-resistant Enterobacter-1 was 1.18-log under 20 mJ/cm~2 UV 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.