| description |
Treated municipal wastewater is implicated in the dissemination of antibiotic-resistant bacteria (ARB) into the environment, and can impose a concern if the treated wastewater were to be reused for agricultural irrigation. This study examined the decay kinetics and molecular responses of a blaNDM-1-positive E. coli PI-7 isolated from wastewater and another blaNDM-1-negative commensal E. coli DSM 1103 upon solar irradiation. Our results found that in buffer solution, the NDM-1 containing E. coli displayed a longer lag-phase prior to decay and a longer half-life compared with the blaNDM-1-negative commensal E. coli (6.64 ± 0.63 h and 2.85 ± 0.46 min vs. 6.64 ± 0.63 h and 2.85 ± 0.46 min). Although solar irradiation remains useful and effective in reducing E. coli cell numbers by more than 5-log in less than 24 h, transcriptomics revealed differences in the overall upregulation of genes between both E. coli strains. A wider arsenal of genes related to oxidative stress, cellular repair and protective mechanisms were upregulated in E. coli PI-7 compared to DSM 1103. Subpopulations of the E. coli PI-7 expressed genes related to dormancy and persister cells formation during the late decay phase, which may have accounted for the prolonged persistence of E. coli PI-7. Upon prolonged solar irradiance, both E. coli strains displayed upregulation of genes related to horizontal gene transfer and antibiotic resistance. Virulence functions unique to blaNDM-1-positive E. coli PI-7 were also upregulated. Our findings collectively indicate that there is a need to place heightened level of concern on dissemination risks arising from the different types of ARB that may still remain viable in the treated wastewater despite having been subjected to solar irradiation. |