Occurrence of high-risk mcr-1 gene and blaNDM-1 positive superbug in the reverse osmosis filter cartridges of the household water purifiers

Household water purifiers (HWPs) are increasingly used to clean water at home, representing the last defense of chemical and microbial contaminants in drinking water. However, little is known about antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs) in the HWPs. Here, we quantified ARB and ARGs on the reverse osmosis (RO) membranes of the HWPs using both culture-dependent and independent approaches. 84 ARGs conferring resistance to 11 antibiotics through three major mechanisms of antibiotic deactivation, efflux, and cellular protection were detected. For the first time, we found high-risk mcr-1, blaIMP, and blaVIM genes in some RO cartridges, which can confer bacterial resistance to the last-resort antibiotics colistin and carbapenems. Furthermore, 27 antibiotic-resistant opportunistic human pathogens were isolated from the RO filters, including a particularly dangerous blaNDM-1 carrying superbug that can transfer blaNDM-1 to the antibiotic susceptible bacteria by conjugation in the laboratory. The potential ARG horizontal transfer on the RO filter was also proposed. Overall, this study characterizes the RO filter-associated ARB and ARGs in HWPs and highlights their potential contaminations in drinking water.