Comprehensive evaluation of UV inactivation of E. coli using multiple gene targets and real-time quantitative PCR

Abstract

UV disinfection is extensively used for wastewater disinfection and disinfection efficiency is commonly monitored using culture-based enumeration of E. coli. While culture-independent real-time quantitative polymerase chain reaction (qPCR) based methods are attractive due to faster turnaround and easier application, previous attempts with qPCR to monitor disinfection have been unsuccessful. In this study, the effect of UV irradiation on a pure E. coli culture was examined in collimated beam (CB) experiments and monitored using both a culturing technique and DNA damage quantified using both short amplicon (SA; <∼200 bp) qPCR and longer amplicon (LA; ∼500-bp) qPCR. The results, covering a UV dose range of 0 - 20 mJ/cm2 commonly used for wastewater disinfection, indicate a correlation between DNA gene damage quantified by both SA- and LA-qPCR and the decline in E. coli observed through culture-based methods. This demonstrates the potential of qPCR to serve as rapid alternative for monitoring wastewater disinfection efficacy. Furthermore, LA-qPCR was observed to be more sensitive than SA-qPCR. The results using LA-qPCR also revealed that UV exposure caused widespread and indiscriminate damage to E. coli’s genome, which is considered critical for its function and survival. The combined effect of UV on E. coli’s ability to function, grow or repair damage is suggested as the reason for the decline in culturability observed.